Development of low-cost frequency-modulated continuous-wave radars at S and W band

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(1)M ÁSTER U NIVERSITARIO EN I NGENIERÍA DE T ELECOMUNICACIÓN. M ASTER T HESIS. Development of low-cost frequency-modulated continuous-wave radars at S and W band. Daniel Montesano Martínez 2019.

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(3) iii. M ÁSTER U NIVERSITARIO EN I NGENIERÍA DE T ELECOMUNI CACIÓN. M ASTER T HESIS Titulo: D EVELOPMENT OF LOW - COST FREQUENCY - MODULATED CONTINUOUS - WAVE RADARS AT S AND W BAND Autor: D ANIEL M ONTESANO M ARTÍNEZ Tutor: F EDERICO G ARCÍA R IAL Ponente: J ESÚS G RAJAL DE LA F UENTE Departamento: D EPARTAMENTO DE S EÑALES , S ISTEMAS Y R ADIOCOMUNICACIONES. M IEMBROS DEL TRIBUNAL Presidente: Vocal: Secretario: Suplente:. Los miembros del tribunal arriba nombrados acuerdan otorgar la calificación de:. Madrid, a. de. de 20.

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(5) U NIVERSIDAD P OLITÉCNICA DE M ADRID. E SCUELA T ÉCNICA S UPERIOR DE I NGENIEROS DE T ELECOMUNICACIONES. M ÁSTER U NIVERSITARIO EN I NGENIERÍA DE T ELECOMUNICACIÓN M ASTER T HESIS. Development of low-cost frequency-modulated continuous-wave radars at S and W band. Daniel Montesano Martínez 2019.

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(7) iii. UNIVERSIDAD POLITÉCNICA DE MADRID. Abstract Escuela Técnica Superior de Ingenieros de Telecomunicaciones Grupo de Microondas y Radar Máster Universitario en Ingeniería de Telecomunicación Development of low-cost frequency-modulated continuous-wave radars at S and W band by Daniel Montesano Martínez. Introduction Continuous-wave radars are capable of measuring distance and radial velocity. For measuring distance, frequency modulation is required. The most common type of modulation is a linear variation of frequency over time. Continuous-wave linear frequency modulated (CW-LFM) radars are used in multiple applications such as proximity sensors, non-intrusive inspection or imaging systems. Objectives This project has two different objectives: • Development of a low-cost CW-LFM radar for radar imaging. Radio frequency elements in a radar imaging system tend to be one of the most expensive parts of the whole system. The project looks for a low-cost alternative of conventional systems. • Development of a low-cost CW-LFM radar for educational use. An adaptable CW-LFM radar is desired while allowing flexible configuration and full characterization of each parameter of the radar. Also, there is the need to obtain the raw samples of the radar, for further processing in a personal computer. Project description This document shows the development of two CW-LFM radars, one at W band and the other at S band. Both bands allocate at least one ISM reserved band, allowing the operation of said radars without license. The advantage of the W band is the availability of huge bandwidths. It is easier to obtain larger bandwidths when operating at higher frequencies. Given the fact that the resolution of a CW-LFM radar is defined by the absolute bandwidth, the use of mm-bands is a good option when looking for large bandwidths. Also, using high frequencies helps to improve the cross-range resolution on a imaging system. The main benefits of the S band are the reduced costs due to wide selection components and low manufacturing costs. The W band radar is based on a commercial MMIC (Monolithic Microwave Integrated Circuit), which provides all the high-frequency elements: oscillator, mixer.

(8) iv and amplifiers among others. This project creates the needed baseband platform for said MMIC, providing the ability for frequency modulation and adapting the signal for the correct acquisition. It is focused on radar imaging. The S band radar originates as an educational project: a very low-cost radar capable of measuring distance and speed. The whole system is designed with commercial integrated circuits. The wide selection of components in the band due to WIFI band overlap, reduces the cost of the system. Also the selected frequency band allows to manufacture the boards without much complexity. In the basic design of this system, every functional block of the radar is isolated and connectorized. With this structure, full characterization of the radar can be achieved, allowing the users to compensate any malfunction of the system. The whole system is configured by a microcontroller, which also samples the signal that will be transmitted to a personal computer via USB. Also, the applications of each radar are studied. Specifically, the W band radar has been integrated in an already-existing passive imaging system..

(9) v Desarrollo de radares de onda continua y frecuencia modulada de bajo coste en banda S y banda W. por Daniel Montesano Martínez Los radares de onda continua son capaces de medir distancia y velocidad radial. Para medir distancia es necesario modular en frecuencia. La modulación más usada es la variación lineal de la frecuencia respecto al tiempo. Los radares de onda continua y frecuencia modulada (CW-LFM por sus siglas en inglés) se usan en varias aplicaciones, tales como sensores de proximidad, inspección no intrusiva de materiales o sistemas de imagen. Objetivos Este proyecto tiene dos objetivos principales: • El desarrollo de un radar CW-LFM para obtener imágenes radar. Los elementos de radio de un sistema de imagen radar suelen ser los más costosos de todo el sistema. Este proyecto busca alternativas a los sistemas convencionales con bajo coste. • El desarrollo de un radar CW-LFM de bajo coste con fines educativos. Es necesario fabricar un radar adaptable y configurable para permitir la caracterización completa de cada elemento del radar. También es necesario tener acceso a las muestras del radar, lo cual permite un procesado posterior en un ordenador personal. Descripción del proyecto Este documento muestra el desarrollo de dos radares CW-LFM: uno en banda W y otro en banda S. Los dos están ubicados en bandas ISM, lo cual permite operar dichos radares sin necesidad de obtener una licencia. La ventaja de operar en banda W es la disponibilidad de grandes anchos de banda, ya que es más sencillo obtener anchos de banda grandes en altas frecuencias. Dado que la resolución del sistema está determinada por el ancho de banda absoluto transmitido, el uso de bandas milimétricas es una buena opción cuando se desean grandes anchos de banda. Además, operar en altas frecuencias ayuda a mejorar la resolución de los pixeles en sistemas de imagen. Los principales beneficios de la banda S son los reducidos costes de componentes y su gran disponibilidad, así como bajos costes de montaje y fabricación. El radar de banda W está basado en un componente comercial, un circuito integrado de microondas (MMIC por sus siglas en ingles), que proporciona todos los elementos de alta frecuencia: osciladores, mezcladores y amplificadores, entre otros. Este proyecto crea la placa de banda base necesaria para dicho MMIC, proporcionando la habilidad de modular en frecuencia y adaptar la señal de salida para una correcta adquisición. Se centra en su uso como radar de imagen. El radar en banda S nace como un proyecto educativo: un radar de coste muy reducido, capaz de medir distancia y velocidad. El sistema completo está compuesto por circuitos integrados comerciales. La gran selección de componentes disponibles en esta banda, debido a su superposición con la banda de wifi, reduce los costes del sistema. Además, dicha banda permite la fabricación de placas sin complejidad. En el diseño más básico de este sistema, todos los bloques funcionales están aislados y.

(10) vi conectorizados. Con esta estructura, se puede conseguir una caracterización completa de cada componente, así como del sistema completo. Esto puede permitir a los usuarios compensar cualquier defecto del sistema. Todo el sistema está configurado por un microcontrolador, que muestrea la señal y la transmite a un ordenador mediante USB. Además, aplicaciones de cada radar son estudiadas. Específicamente, el radar de banda W se ha integrado en un sistema de imagen pasivo ya existente..

(11) vii. Acknowledgements This master thesis is the result of several months of dedication and hard work. However, it could not have been possible without the collaboration of many people I would like to give recognition to. First of all, my supervisor Federico, who has always given me its unconditional help. He has dedicated a lot of time teaching me how to operate in the laboratory and the basis knowledge about radars, providing me the pillars of my work experience. He introduced me to the research group and its colleagues, and he taught me how to move around it. My colleague Luis Alberto is a key piece in this master thesis, since he has collaborated in it by developing some essential blocks of this project. Also, he has always been helpful with any technical problem and his curiosity has been always a motivation to teardown any device and learn about it. This thesis has been performed under the direction of the professor Jesus Grajal, and I am grateful of working with him, since I have always had all the needed resources for the project at my disposal. I would also like to thank my classmates who became my friends: Paula, Miguel, Amadeo, Daniel, Fran and Hector. We have suffered together during six years, and with their help and company, the path through the ETSIT has been less frustrating. Bilyana has been a constant in my life along all these years, and I would like to thank her for her support and motivation along all my studies, and for being always there for me when I needed it. Finally, I would thank my family for their love and support. Specially to my parents, who have always motivated and helped me along my whole life, becoming who I am thanks to them..

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(13) ix. Contents Abstract. iii. Acknowledgements. vii. 1. 2. Introduction 1.1 Objectives . . . . . . . . . . . 1.2 Fulfillment . . . . . . . . . . . 1.3 CW-LFM radar fundamentals 1.3.1 Working principles . . 1.3.2 Architecture . . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. S band sensor 2.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . 2.2 First version of the S band radar . . . . . . . . . . . 2.2.1 Proposed system . . . . . . . . . . . . . . . . 2.2.2 Component selection . . . . . . . . . . . . . . 2.2.3 Board layout . . . . . . . . . . . . . . . . . . . 2.2.4 Component characterization . . . . . . . . . 2.2.4.1 VCO . . . . . . . . . . . . . . . . . . 2.2.4.2 Power amplifier and coupler . . . . 2.2.4.3 Low noise amplifier . . . . . . . . . 2.2.4.4 Mixer . . . . . . . . . . . . . . . . . 2.2.4.5 Through lines . . . . . . . . . . . . 2.2.4.6 Signal conditioning stage . . . . . . 2.2.5 Complete system measurements . . . . . . . 2.3 Second version of the S band radar . . . . . . . . . . 2.3.1 Proposed modified system . . . . . . . . . . 2.3.1.1 Proposed architecture . . . . . . . . 2.3.2 Component selection . . . . . . . . . . . . . . 2.3.2.1 Component simulation . . . . . . . 2.3.3 Design and manufacturing . . . . . . . . . . 2.3.4 Component characterization . . . . . . . . . 2.3.4.1 VCO and power splitter . . . . . . . 2.3.4.2 Power amplifier . . . . . . . . . . . 2.3.4.3 Low Noise Amplifier . . . . . . . . 2.3.4.4 Quadrature demodulator . . . . . . 2.3.4.5 Baseband filters . . . . . . . . . . . 2.3.5 Complete system measurements . . . . . . . 2.3.5.1 Comparison with previous version. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . .. 1 1 2 2 2 4. . . . . . . . . . . . . . . . . . . . . . . . . . . .. 5 5 7 7 9 11 13 13 17 22 23 25 26 31 35 35 36 37 40 41 43 43 47 49 51 55 57 61.

(14) x 3. W band sensor 3.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2 State of Art . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.1 Available options . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3 Initial design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4 First version of the W band radar . . . . . . . . . . . . . . . . . . . . . . 3.4.1 Proposed modifications . . . . . . . . . . . . . . . . . . . . . . . 3.4.1.1 Compatible pinout . . . . . . . . . . . . . . . . . . . . . 3.4.1.2 I/Q signals . . . . . . . . . . . . . . . . . . . . . . . . . 3.4.1.3 PFD configuration . . . . . . . . . . . . . . . . . . . . . 3.4.1.4 Microcontroller . . . . . . . . . . . . . . . . . . . . . . . 3.4.1.5 Power consumption . . . . . . . . . . . . . . . . . . . . 3.4.1.6 Trigger . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4.1.7 Clock . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4.2 Board design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4.3 Manufacturing . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4.4 Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4.4.1 VCO ramp . . . . . . . . . . . . . . . . . . . . . . . . . 3.4.4.2 Trigger . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4.4.3 Clock . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4.4.4 Beat signal spectrum . . . . . . . . . . . . . . . . . . . 3.4.4.5 MMIC bandwidth . . . . . . . . . . . . . . . . . . . . . 3.4.4.6 Range resolution . . . . . . . . . . . . . . . . . . . . . . 3.4.4.7 I/Q filters . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4.4.8 Phase stability . . . . . . . . . . . . . . . . . . . . . . . 3.4.4.9 Power consumption . . . . . . . . . . . . . . . . . . . . 3.5 Second version of the W band radar . . . . . . . . . . . . . . . . . . . . 3.5.1 Proposed modifications . . . . . . . . . . . . . . . . . . . . . . . 3.5.1.1 Frequency divider configuration . . . . . . . . . . . . . 3.5.1.2 Clock selection . . . . . . . . . . . . . . . . . . . . . . . 3.5.1.3 Microcontroller . . . . . . . . . . . . . . . . . . . . . . . 3.5.1.4 Power supply . . . . . . . . . . . . . . . . . . . . . . . 3.5.1.5 MMIC board . . . . . . . . . . . . . . . . . . . . . . . . 3.5.1.6 PFD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5.1.7 Clock board . . . . . . . . . . . . . . . . . . . . . . . . . 3.5.1.8 I/Q filters . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5.1.9 PLL filter . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5.2 Board design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5.2.1 Slave board . . . . . . . . . . . . . . . . . . . . . . . . . 3.5.2.2 Clock board . . . . . . . . . . . . . . . . . . . . . . . . . 3.5.2.3 MMIC board . . . . . . . . . . . . . . . . . . . . . . . . 3.5.3 Manufacturing . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5.4 Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5.4.1 IQ filters . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5.4.2 MMIC bandwidth . . . . . . . . . . . . . . . . . . . . . 3.5.4.3 Phase noise comparison between reference oscillators 3.5.4.4 Multi board synchronization . . . . . . . . . . . . . . . 3.5.4.5 Power consumption . . . . . . . . . . . . . . . . . . . . 3.5.4.6 Beamwidth . . . . . . . . . . . . . . . . . . . . . . . . . 3.6 Imager . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.6.1 System description . . . . . . . . . . . . . . . . . . . . . . . . . .. 63 63 63 64 65 70 71 72 72 73 75 75 76 76 77 80 82 82 83 83 85 86 88 89 90 91 92 92 95 95 96 97 98 99 101 102 107 111 111 113 114 115 119 119 121 122 124 125 126 132 132.

(15) xi 3.6.2 4. 3D images . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133. Conclusions. 139. A W band first version operation guide. 141. B W band second version operation guide B.1 VUSB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B.2 Bootloader . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B.3 Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . B.3.1 Analog Devices software and Arduino IDE for flashing B.3.2 Matlab configuration and Arduino IDE flashing . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. 155 155 155 157 157 157. C Evaluation board for ADRF6516 C.1 Design . . . . . . . . . . . . . . . . . . . C.2 Manufacturing . . . . . . . . . . . . . . . C.3 Characterization . . . . . . . . . . . . . . C.4 ADRF6516 evaluation board schematic . C.5 ADRF6516 evaluation board layout . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. 169 169 170 170 172 177. D Schematics and layouts D.1 First version of the S band radar . . . . . . . . . . . . . . . . . . . . D.1.1 Band S first version schematics . . . . . . . . . . . . . . . . . D.1.2 Band S first version layout . . . . . . . . . . . . . . . . . . . . D.2 Second version of the S band radar . . . . . . . . . . . . . . . . . . . D.2.1 Band S second version schematics . . . . . . . . . . . . . . . D.2.2 Band S second version layout . . . . . . . . . . . . . . . . . . D.3 First version of the W band radar . . . . . . . . . . . . . . . . . . . . D.3.1 W band first version schematics . . . . . . . . . . . . . . . . D.3.2 W band first version layout . . . . . . . . . . . . . . . . . . . D.4 Second version of the W band radar . . . . . . . . . . . . . . . . . . D.4.1 W band second version. MMIC board schematics . . . . . . D.4.2 W band second version. MMIC board layout . . . . . . . . . D.4.3 W band second version. MMIC board with MHF schematics D.4.4 W band second version. MMIC board with MHF layout . . D.4.5 W band second version. Main board schematics . . . . . . . D.4.6 W band second version. Main board layout . . . . . . . . . . D.4.7 W band second version. Master board schematics . . . . . . D.4.8 W band second version. Master board layout . . . . . . . . . D.4.9 W band second version. Panelized board layout . . . . . . .. . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . .. 179 179 180 186 190 191 199 203 204 208 210 211 212 216 217 221 230 234 239 243. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. E Digital Subsystem 247 E.1 Digital Subsystem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248 F BOM and costs F.1 S band first version . . F.2 S band second version F.3 W band first version . F.4 W band second version. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. 257 257 257 258 258.

(16) xii G W band commercial kit. Extended mode G.1 Protocol description . . . . . . . . . . . G.1.1 Backend to frontend . . . . . . G.1.2 Frontend to backend . . . . . . G.2 Developed code . . . . . . . . . . . . . G.2.1 Function readAndPlot.m . . . G.2.2 Function txt2plot.m . . . . . . . G.2.2.1 Phase data frame . . . G.2.2.2 Range data frame . . G.2.2.3 CFAR data frame . . G.2.2.4 Target list data frame G.2.2.5 Status data frame . . G.2.2.6 Error data frame . . . G.2.3 Function extData.m . . . . . . . G.2.4 Data frames . . . . . . . . . . .. . . . . . . . . . . . . . .. . . . . . . . . . . . . . .. . . . . . . . . . . . . . .. . . . . . . . . . . . . . .. . . . . . . . . . . . . . .. . . . . . . . . . . . . . .. . . . . . . . . . . . . . .. . . . . . . . . . . . . . .. . . . . . . . . . . . . . .. . . . . . . . . . . . . . .. . . . . . . . . . . . . . .. . . . . . . . . . . . . . .. . . . . . . . . . . . . . .. 261 261 261 262 262 262 263 263 263 264 264 264 264 264 264. H Environmental, social and economical impact H.1 Introduction . . . . . . . . . . . . . . . . . . . . . . H.2 Relevant impact description related to the project H.2.1 Privacy . . . . . . . . . . . . . . . . . . . . . H.2.2 Health . . . . . . . . . . . . . . . . . . . . . H.2.2.1 Millimeter wave scanners . . . . . H.2.2.2 Backscatter X-ray scanners . . . . H.3 Analysis . . . . . . . . . . . . . . . . . . . . . . . . H.3.1 Privacy . . . . . . . . . . . . . . . . . . . . . H.3.2 Health . . . . . . . . . . . . . . . . . . . . . H.4 Conclusions . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . .. . . . . . . . . . .. . . . . . . . . . .. . . . . . . . . . .. . . . . . . . . . .. . . . . . . . . . .. . . . . . . . . . .. . . . . . . . . . .. . . . . . . . . . .. . . . . . . . . . .. . . . . . . . . . .. . . . . . . . . . .. 283 283 283 283 284 284 284 284 285 285 285. I. . . . . . . . . . . . . . .. . . . . . . . . . . . . . .. . . . . . . . . . . . . . .. . . . . . . . . . . . . . .. . . . . . . . . . . . . . .. . . . . . . . . . . . . . .. Economic budget 287 I.1 Development costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287 I.2 Manufacturing costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 288 I.3 Project budget . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 288. Bibliography. 289.

(17) xiii. List of Figures 1.1 1.2 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 2.10 2.11 2.12 2.13 2.14 2.15 2.16 2.17 2.18 2.19 2.20 2.21 2.22 2.23 2.24 2.25 2.26 2.27 2.28 2.29 2.30 2.31 2.32 2.33 2.34. Frequency of the transmitted, received and beat frequencies for a single target in an CW-LFM radar. . . . . . . . . . . . . . . . . . . . . . . . Architecture of a generic CW-LFM radar. . . . . . . . . . . . . . . . . . Architecture of the first version of the developed system . . . . . . . Photo of the manufactured PCB with the functional blocks identified. Photo of the mounted VCO. . . . . . . . . . . . . . . . . . . . . . . . . Photo of the mounted PA. . . . . . . . . . . . . . . . . . . . . . . . . . Photo of the mounted coupler. . . . . . . . . . . . . . . . . . . . . . . . Photo of the mounted LNA. . . . . . . . . . . . . . . . . . . . . . . . . Photo of the mounted mixer. . . . . . . . . . . . . . . . . . . . . . . . . Photo of the conditioning stage. . . . . . . . . . . . . . . . . . . . . . . Buildup of EuroCircuits 4 layers PCB . . . . . . . . . . . . . . . . . . . Layout of the first version of S band radar. . . . . . . . . . . . . . . . . VCO tuning curve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VCO output power variation along frequency . . . . . . . . . . . . . Three tones generated with USB powering. . . . . . . . . . . . . . . . VCO phase noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Voltage ramp generated by the DAC. . . . . . . . . . . . . . . . . . . . S parameters of the power amplifier and coupler block. . . . . . . . . S parameters of the manufacturer of the power amplifier block components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Evolution of output power versus the input power for the PA. . . . . Variation of output power of the PA along the spectrum. . . . . . . . Power spectrum of the power amplifier when fed by the VCO. . . . . The PCB with the isolated power amplifier. . . . . . . . . . . . . . . . S parameters of the isolated power amplifier. . . . . . . . . . . . . . . The modified PCB to isolate the coupler. . . . . . . . . . . . . . . . . . Measured S parameters of the isolated coupler. . . . . . . . . . . . . . Measured S parameters of the LNA. . . . . . . . . . . . . . . . . . . . Gain variation versus input power of LNA . . . . . . . . . . . . . . . Isolation between RF and LO ports. . . . . . . . . . . . . . . . . . . . . Isolation between LO and IF ports. . . . . . . . . . . . . . . . . . . . . Through lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . S parameters of through lines. . . . . . . . . . . . . . . . . . . . . . . . Signal conditioning stage architecture . . . . . . . . . . . . . . . . . . Schematics of second stage. . . . . . . . . . . . . . . . . . . . . . . . . Schematics of first option of first substage of the signal conditioning stage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Frequency response of first option of first substage of the signal conditioning stage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 3 4. . . . . . . . . . . . . . . . .. 8 8 10 10 10 11 11 11 12 12 14 15 15 16 16 18. . . . . . . . . . . . . . . . .. 18 19 20 20 21 21 22 22 23 23 25 25 25 26 26 27. . 28 . 29.

(18) xiv 2.35 Schematics of the second option of first substage of the signal conditioning stage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.36 Frequency response of second option of the first substage of the signal conditioning stage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.37 A 26 m long cable measured with different BW. . . . . . . . . . . . . . . 2.38 Satellite image of the measured scenario obtained from Google Maps. . 2.39 Measured building 31 m away. . . . . . . . . . . . . . . . . . . . . . . . 2.40 Satellite image of the measured scenario obtained from Google Maps. . 2.41 Open space setup: the radar mounted on a tripod with dipole antennas. 2.42 Moving vehicles measurement. . . . . . . . . . . . . . . . . . . . . . . . 2.43 Architecture of the second version of the S band radar . . . . . . . . . . 2.44 Architecture of the first version of the S band radar . . . . . . . . . . . 2.45 Photo of the mounted VCO. . . . . . . . . . . . . . . . . . . . . . . . . . 2.46 Photo of the mounted PA. . . . . . . . . . . . . . . . . . . . . . . . . . . 2.47 Photo of the mounted power splitter. . . . . . . . . . . . . . . . . . . . . 2.48 Photo of the mounted LNA. . . . . . . . . . . . . . . . . . . . . . . . . . 2.49 Photo of the mounted mixer. . . . . . . . . . . . . . . . . . . . . . . . . . 2.50 Photo of the balun. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.51 Diagram of the power stage of the second S band version . . . . . . . . 2.52 Photo of the Vivaldi antennas. . . . . . . . . . . . . . . . . . . . . . . . . 2.53 Budget simulation in ADS of the proposed system. . . . . . . . . . . . . 2.54 Return loss of the Vivaldi antennas. . . . . . . . . . . . . . . . . . . . . . 2.55 Results of the ADS budget simulation. . . . . . . . . . . . . . . . . . . . 2.56 Layout of the second version of S band radar. . . . . . . . . . . . . . . . 2.57 Photo of the manufactured board. . . . . . . . . . . . . . . . . . . . . . . 2.58 Architecture of the DAC amplifier. . . . . . . . . . . . . . . . . . . . . . 2.59 Tuning voltage of the VCO. . . . . . . . . . . . . . . . . . . . . . . . . . 2.60 Spectrum of the VCO. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.61 Phase noise of the VCO. . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.62 S parameters of the power amplifier . . . . . . . . . . . . . . . . . . . . 2.63 Output power versus input power of the power amplifier. . . . . . . . 2.64 Spectrum of the power amplifier driven by the VCO. . . . . . . . . . . 2.65 S parameters of the LNAs . . . . . . . . . . . . . . . . . . . . . . . . . . 2.66 Gain variation along input power of the LNA1. . . . . . . . . . . . . . . 2.67 Configuration values used for setting the 1-dB cutoff frequency of the baseband low pass filter of the mixer. . . . . . . . . . . . . . . . . . . . . 2.68 Output spectrum of the mixer for different cutoff frequencies configurations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.69 Output spectrum of the mixer for different gain configurations. . . . . 2.70 Gain variation along LO input power. . . . . . . . . . . . . . . . . . . . 2.71 Gain variation of the mixer along LO frequency. . . . . . . . . . . . . . 2.72 Gain mismatch between mixer I/Q outputs. . . . . . . . . . . . . . . . . 2.73 Return loss of the mixer RF and LO ports. . . . . . . . . . . . . . . . . . 2.74 Architecture of the baseband filters. . . . . . . . . . . . . . . . . . . . . 2.75 Response of the baseband filters. . . . . . . . . . . . . . . . . . . . . . . 2.76 Response of the combined mixer and baseband filters. . . . . . . . . . . 2.77 A 26 m long cable measured with different BW. . . . . . . . . . . . . . . 2.78 Satellite image of the measured scenario obtained from Google Maps. . 2.79 Building measurement setup: the radar mounted on a tripod with the Vivaldi antennas. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 29 30 32 32 32 33 33 34 36 36 37 37 37 38 38 38 39 40 41 41 41 42 43 44 45 46 46 47 48 49 50 50 52 52 53 53 53 54 54 55 56 56 57 58 58.

(19) xv 2.80 Comparison of measurements of a building 31 m away using the S band radar with different bandwidth. . . . . . . . . . . . . . . . . . . . 2.81 Satellite image of the measured scenario obtained from Google Maps. . 2.82 Open space setup: the radar mounted on a tripod with the Vivaldi antennas. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.83 Moving vehicles measurement. . . . . . . . . . . . . . . . . . . . . . . . 2.84 Doppler measurement of moving vehicles. . . . . . . . . . . . . . . . . 2.85 Comparison of the building measurement between both versions . . . 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 3.10 3.11 3.12 3.13 3.14 3.15 3.16 3.17 3.18 3.19 3.20 3.21 3.22 3.23 3.24 3.25 3.26. 3.27 3.28 3.29 3.30 3.31 3.32 3.33 3.34 3.35. Silicon Radar’s 122 GHz CW-LFM radar evaluation kit called EasyRad. Architecture of EasyRad. . . . . . . . . . . . . . . . . . . . . . . . . . . . GUI provided with the evaluation kit. Spectrum generated by a metallic target at 1 m. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Matlab GUI with an spectrum of a metallic target at 1 m. . . . . . . . . Voltage ramps at the input of the VCO in EasyRad . . . . . . . . . . . . Spectrum and I/Q data from a metallic sheet 1 m away. . . . . . . . . . Architecture of the first version. . . . . . . . . . . . . . . . . . . . . . . . Designed pinout with main connections tagged. . . . . . . . . . . . . . Location of connectors in the commercial kit. . . . . . . . . . . . . . . . Output buffers for the I/Q signals. . . . . . . . . . . . . . . . . . . . . . Visual explanation of three PFD operating modes . . . . . . . . . . . . Photo of the Arduino Nano board. . . . . . . . . . . . . . . . . . . . . . Diagram of the power distribution in the board. . . . . . . . . . . . . . Modification of the baseband board for the extraction of the reference. First version design layout of the W band radar. . . . . . . . . . . . . . Schematics of the frequency divider configuration switches. . . . . . . Photo of the manufactured PCB, configured and ready for operation. . Comparison between voltage ramps of the initial system and the developed board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Setup for the measurement of the VCO voltage ramp. . . . . . . . . . . Comparison of the trigger before and after the comparator. . . . . . . . Impact of the frequency divider. . . . . . . . . . . . . . . . . . . . . . . . Phase noise produced by the divider. . . . . . . . . . . . . . . . . . . . . Comparison between spectrums of a same target using the original design and after the modifications. . . . . . . . . . . . . . . . . . . . . . Spectrum with a target 4 m away. . . . . . . . . . . . . . . . . . . . . . . Reflected power along frequency. . . . . . . . . . . . . . . . . . . . . . . Setup for the measurement of the divided VCO output. The high frequency probe is touching one of the two differential outputs of the divided signal. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Frequency sweep at the VCO output divided by 64. . . . . . . . . . . . Diagram of the performed experiment to measure the range resolution. Range resolution of the first version design . . . . . . . . . . . . . . . . Measured gain of the first version of the W band radar. . . . . . . . . . Measurement of the radar phase stability . . . . . . . . . . . . . . . . . Photo of the two manufactured boards: first version (left) and second version (right). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Two available MMIC boards. . . . . . . . . . . . . . . . . . . . . . . . . Proposed architecture for the second version design. . . . . . . . . . . . Architecture of the first version for comparison. . . . . . . . . . . . . .. 59 60 60 61 61 62 65 66 67 67 68 69 71 72 72 73 74 75 76 77 78 79 81 82 83 83 84 85 85 86 87. 87 88 88 89 90 91 92 93 94 94.

(20) xvi 3.36 Comparison between the frequency divider in both versions. The area shown in the images is the same. . . . . . . . . . . . . . . . . . . . . . 3.37 Architecture of the reference selector. . . . . . . . . . . . . . . . . . . . 3.38 Power distribution for the second version of the W band radar. . . . 3.39 Definition of the MMIC board connectors. . . . . . . . . . . . . . . . . 3.40 Detail of the MMIC board with connectors. The blue line shows the buried path that connects the divided signal with the pin. . . . . . . . 3.41 Architecture of a charge pump. . . . . . . . . . . . . . . . . . . . . . . 3.42 Diagram of the synchronism architecture. . . . . . . . . . . . . . . . . 3.43 Chirps of two nodes interfering between them, and the interfering beat frequency of the first node caused by the second node . . . . . . 3.44 Layout of the two superposed oscillators . . . . . . . . . . . . . . . . 3.45 Photo of the custom-made evaluation board for ADRF6516 . . . . . . 3.46 Comparison of the ADRF6516 noise floor and the original system dynamic range. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.47 Variation of the ADRF6516 noise floor along gain. . . . . . . . . . . . 3.48 Proposed architecture for the I/Q filtering amplifiers. . . . . . . . . . 3.49 Simulated frequency response of proposed I/Q filters. . . . . . . . . . 3.50 Architecture of passive third-order filter for charge pumps. . . . . . . 3.51 Simulated loop gain of the PLL. . . . . . . . . . . . . . . . . . . . . . . 3.52 Simulated phase noise of the system . . . . . . . . . . . . . . . . . . . 3.53 Frequency deviation and error of a chirp. . . . . . . . . . . . . . . . . 3.54 Response of the system when sweeping the full bandwidth in the minimum posible time. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.55 Active PLL filter considered for the PCB design. . . . . . . . . . . . . 3.56 Top layout of the slave board. . . . . . . . . . . . . . . . . . . . . . . . 3.57 Bottom layout of the slave board. . . . . . . . . . . . . . . . . . . . . . 3.58 Relative distances from the lens mounting holes to the MMIC board connectors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.59 Top view of the stacked up boards. . . . . . . . . . . . . . . . . . . . 3.60 Top layout of the master board. . . . . . . . . . . . . . . . . . . . . . . 3.61 The two different manufactured MMIC boards. . . . . . . . . . . . . . 3.62 Buildup of EuroCircuits 4 layers PCB . . . . . . . . . . . . . . . . . . . 3.63 Top view of the panelized boards. . . . . . . . . . . . . . . . . . . . . . 3.64 Equivalent circuit of the proposed solutions. . . . . . . . . . . . . . . 3.65 Modifications to fix the frequency divider design error. . . . . . . . . 3.66 Footprints of master oscillator. . . . . . . . . . . . . . . . . . . . . . . 3.67 Stack-up of the manufactured boards. . . . . . . . . . . . . . . . . . . 3.68 Manufactured MMIC board with MHF connectors. . . . . . . . . . . 3.69 Photo of the modification performed to one MMIC board to inject a signal to I/Q filters through coaxial. . . . . . . . . . . . . . . . . . . . 3.70 Measured gain of the designed I/Q filters . . . . . . . . . . . . . . . . 3.71 Comparison of the I/Q filter’s response between the second version and the original system. . . . . . . . . . . . . . . . . . . . . . . . . . . 3.72 Measured bandwidth of the TRX_120_012 MMIC. . . . . . . . . . . . 3.73 Bandwidth comparison for the TRX_120_001 MMIC between first and second design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.74 Phase noise of available sources. . . . . . . . . . . . . . . . . . . . . . 3.75 Effects of several reference oscillators on phase noise measured in the feedback loop of the PLL . . . . . . . . . . . . . . . . . . . . . . . . . . 3.76 Effects on the spectrum due to the reference oscillator phase noise. .. . . . .. 95 96 97 98. . 99 . 100 . 100 . 100 . 102 . 103 . . . . . . . .. 104 104 105 107 108 109 109 110. . . . .. 110 111 112 112. . . . . . . . . . . .. 113 113 114 115 115 116 117 118 118 118 118. . 119 . 120 . 120 . 121 . 122 . 123 . 123 . 124.

(21) xvii 3.77 3.78 3.79 3.80 3.81 3.82 3.83 3.84 3.85 3.86 3.87 3.88 3.89 3.90 3.91 3.92. Oscilloscope capture showing two boards synchronized. . . . . . . . . 124 Side view of the dielectric lens. . . . . . . . . . . . . . . . . . . . . . . . 127 The lens mounted on a PCB with 10 mm separators. . . . . . . . . . . . 127 Dielectric lens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127 The designed turntable for beamwidth measurements mounted on a tripod. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128 Photo of the MMIC with the exposed antennas obtained from its datasheet129 Radiation pattern of the patch antennas MMIC without lens. . . . . . . 129 E plane radiation pattern of the patch antennas with lens. . . . . . . . . 130 A photo of the Wavecamm product . . . . . . . . . . . . . . . . . . . . . 132 Reflector system of the imager. . . . . . . . . . . . . . . . . . . . . . . . 133 Diagram of the FoV scan achieved by the reflector system . . . . . . . . 133 Scanned scenario with the dummy target. . . . . . . . . . . . . . . . . . 134 The first version of the W band radar mounted on the reflector system. 134 The dummy as a target scanned with the first version sensor . . . . . . 135 The second version of the W band radar mounted on the reflector system. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136 The dummy as a target scanned with the second version sensor . . . . 136. A.1 The jumper placed in the pin 37 of JP3, enabling a 10 dB attenuator. . . 143 A.2 Capture of the trigger and I and Q signals for a 150 µS ramp with 6.3 GHz of bandwidth. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144 C.1 C.2 C.3 C.4. Photo of the manufactured evaluation board of ADRF6516. . . . Output spectrum of the ADRF6516. . . . . . . . . . . . . . . . . . Spectrum for different bandwidth configurations. . . . . . . . . Noise floor of the ADRF 6516 with different gain configurations.. . . . .. . . . .. . . . .. . . . .. 170 171 171 171.

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(23) xix. List of Tables 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 2.10 2.11. Comparison between versions of the S band radar. . . . . . VCO datasheet parameters. . . . . . . . . . . . . . . . . . . Main datasheet parameters of the selected power amplifier Main datasheet parameters of the selected coupler. . . . . . Main parameters of low noise amplifier. . . . . . . . . . . . Main parameters of mixer. . . . . . . . . . . . . . . . . . . . VCO parameters provided by the manufacturer. . . . . . . Power splitter datasheet parameters. . . . . . . . . . . . . . Main parameters of the power amplifier . . . . . . . . . . . Main parameters of the low noise amplifier. . . . . . . . . . Main parameters of the quadrature demodulator. . . . . .. . . . . . . . . . . .. . . . . . . . . . . .. . . . . . . . . . . .. . . . . . . . . . . .. . . . . . . . . . . .. . . . . . . . . . . .. . . . . . . . . . . .. 6 13 17 17 22 24 43 44 47 49 51. 3.1. Power consumption of each of the board components. . . . . . . . . . . 76. A.1 Position of the switches for the configuration of the division factor . . 141 F.1 F.2 F.3 F.4. Component costs of the first version of the S band radar. . . Component costs of the second version of the S band radar. . Component costs of the first version of the W band radar. . . Component costs of the second version of the W band radar.. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. 257 258 258 259. I.1 I.2 I.3 I.4. Equipment costs . . . Labour time costs . . Manufacturing costs Project budget . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. 287 287 288 288. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . ..

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(25) xxi. List of Abbreviations ADC BOM BPF BW CP CW DAC DDS DSP FFT FoV HPF IC IDE IF LFM LO LoS LPF LVCMOS LVPECL MFB MMIC MUR NF NDT PCB PFD RC RF SMT SoC SPST VCO. Analog to Digital Converter Bill Of Materials Band Pass Filter Bandwidth Charge Pump Continuous Wave Digital to Analog Converter Direct Digital Synthesis Digital Signal Processor Fast Fourier Transform Field of View High Pass Filter Integrated Circuit Integrated Development Enviroment Intermediate Frequency Linear Frequency Modulation Local Oscilator Line of Sight Low Pass Filter Low Voltage Complementary Metal Oxide Low Voltage Emitter Coupled Logic Multiple FeedBack filters Monolithic Microwave Integrated Circuits Maximum Unambiguous Range Noise Figure Nono Destructive Testing Printed Circuit Board Phase Frequency Detector Resitor Capacitor Radio Frequency Range Surface Mount Technology System on Chip Single Pole Single Through Voltage Controlled Oscilator.

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(27) xxiii. Dedicado a mi novia Bilyana, mi única constante a lo largo de este mundo de Telecomunicaciones lleno de incógnitas y variables..

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(29) 1. Chapter 1. Introduction The research of this master thesis is directed towards the development of a low-cost 3D radar at the Grupo de Microondas y Radar (GMR) of the Universidad Politécnica de Madrid. The system can be used as a security system, assisting in the detection of hidden threats under people’s clothes. For this purpose, a continuous-wave linear frequency modulated (CW-LFM) radar is the selected technology, due to the existing experience of the GMR in such systems [1] [2]. A mm-wave radar is desired because of the spatial resolution and penetration capabilities of those wavelengths, thus the W band is selected as the required frequency band. Working at such a high frequency band may cause difficulties and cost related problems. Because of it, a lower frequency radar is previously developed, helping in the understanding and operation of CW-LFM radars. For this first design, the S band is selected as the working frequency band, since wireless communication in this band (WIFI, Bluetooth and WIMAX, among others) promotes great availability of low-cost components. This version allows prototyping and testing different architectures at a fraction of the cost of the corresponding high frequency version. The knowledge obtained from the S band is applied in the development of the W band radar. Since the budget is restricted, no custom-made equipment should be used. A reduced-cost alternative is to develop a system from commercially available sensors, as the one developed in this master thesis. It is based on an preexisting passive imager working at 94 GHz [3], with the integration of a modified commercial 122 GHz CW-LFM radar [4]. The modification of the active sensor and the integration is executed in this master thesis. The combination of both sensors creates a low-cost 3D radar imager, capable of screening people and detect hidden threats under clothes.. 1.1. Objectives. The main objective of this master thesis is the development of a low-cost CW-LFM radar for its integration into an imager system working at W band. This radar should be compact and capable of penetrating clothes and detecting hidden threats. To achieve this, a S band CW-LFM radar is previously developed for testing and prototyping. Additionally, the S band radar should be able to measure distance and speed. Although speed is not necessary for imaging, it can be useful in other applications such as vital signs monitoring..

(30) Chapter 1. Introduction. 2. 1.2. Fulfillment. The evolution of this project is presented along this master thesis. The developed radars are shown, as well as the integration in the imager system. The S band radar has been developed and tested. It is capable of measuring distances up to 130 m, greater than the typical imager stand-off distance (2-25m) [2] [5] [6]. Also it is capable of measuring moving objets faster than 5 Km/h. The development of this radar is detailed in Chapter 2. The W band radar is developed by modifying and improving a commercial system. This modification allows the detection of farther targets and the measurement of sub-mm distance variations. Also, it allows to manufacture multiple systems, which can be converted in a sensor network capable of measuring a target from different points of view. The development of this radar is detailed in Chapter 3. With the integration of the W band radar in the imager, 3D images of a person have been obtained, as well as the detection of hidden threats under the clothes. This integration as well as its results can be seen in Section 3.6.. 1.3 1.3.1. CW-LFM radar fundamentals Working principles. The working principle of CW-LFM radars is based on the reception of a reflection of the transmitted signal from the target. The transmitted signal has constant amplitude while the frequency is linearly modulated. The instant frequency of the signal linearly variates in a set time, called chirp time or Tc, along a frequency band, ∆ f . The mathematic expression of the transmitted signal is presented in Equation 1.1. At is the constant amplitude, f c is the carrier frequency and m(t) is the modulating signal. Z ∆f Stx (t) = Atx cos(2π f c t + φ + 2π m(t)dt) (1.1) 2 The theoretical received signal is an attenuated and delayed sample of the transmitted signal. With only one target reflecting the transmitted signal, the received signal can be expressed as in Equation 1.2. The delay τ is the travelling time from the transmitter to the target and can be calculated as τ = R/c, with R being the distance to the target and c the speed of the signal in the medium. ∆f Srx (t) = Arx cos(2π f c (t − 2τ ) + φ + 2π m((t − 2τ ))dt) (1.2) 2 In the receiver, the transmitted signal is mixed with the received signal, obtaining the beat signal. The frequency of the beat signal will be the difference between the instantaneous transmitted frequency and the instantaneous received frequency. Accordingly, the beat frequency will be constant between τ and Tc , and its value can be calculated from Equation 1.3. Z. f beat =. ∆ f 2R cTc. (1.3). The theoretical range resolution of CW-LFM radars can be obtained from the range expresion, presented in Equation 1.4. As can be seen, the resolution of the system only depends on the transmitted bandwidth..

(31) 1.3. CW-LFM radar fundamentals. 3. ∆R =. c 2∆ f. (1.4). Frequency [Hz]. Frequency [Hz]. If a sawtooth signal is used as modulating signal, as shown in the top of Figure 1.1, it produces the received signal of the same figure and the beat signal of the bottom figure. The modulating signals most used are sawtooth and triangular. Tx and Rx chirps Tx signal Rx signal. Time [S] Beat frequency. Time [S]. F IGURE 1.1: Frequency of the transmitted, received and beat frequencies for a single target in an CW-LFM radar.. The processing method for CW-LFM is based on the sampling of the beat signal and the application of a fast fourier transform (FFT). The output of the FFT shows the decomposition of the frequency components of the beat signals. This allows the detection of an isolated tone, corresponding to a target illuminated by the radar. The distance to the target can be obtained from the previously mentioned Equation 1.3. With the goal of exposing targets that can be masked by other target’s lateral lobes, the signal can be windowed before applying the FFT. This operation reduces the lateral lobes in the frequency spectrum, at the expense of expanding the main lobe of the target, thus deteriorating the system’s range resolution. It is widened by a factor α, resulting in the range resolution of the Equation 1.5. With a rectangular window, the lateral lobes are at -13dBc, with α=1. On the other hand, when applying a Hamming window, the lobes are reduced to -43dBc but the range resolution is widened by α=1.82. ∆R =. c α 2∆ f. (1.5). The maximum unambiguous range (MUR) of the system is directly related to the maximum detectable frequency, given by the combination of sampling frequency, sweep time and bandwidth. CW-LFM radars present advantages against other kind of radars, like pulsed radars. CW radars are operated with lower power levels, since the average power is equal to the peak power. Also, the system resolution is detached from the MUR. By varying the chirp time, the MUR can be modified, assuming that the sampling frequency and the bandwidth are fixed by design. A more detailed explanation about CW-LFM radars can be found in [7]..

(32) Chapter 1. Introduction. 4. 1.3.2. Architecture. The basic architecture of a CW-LFM radar in an homodyne configuration can be seen in Figure 1.2. The received signal is mixed with a sample of the transmitted signal. For the generation of the chirp signal, several methods can be used. The most popular are direct digital synthesis (DDS) or the use of a voltage controlled oscillator (VCO). Along this master thesis, DDS aren’t used in any design, so they aren’t considered.This is due to the increment of complexity in the implementation. Therefore, VCOs are used for signal generation. Several amplifiers can be used along the signal path, usually a power amplifier (PA) feeding the transmitting antenna and a low noise amplifier (LNA) are used. The beat signal from the mixer is digitalized and processed by an ADC and PC, respectively .. F IGURE 1.2: Architecture of a generic CW-LFM radar..

(33) 5. Chapter 2. S band sensor In this chapter, the development of the S band radar is detailed. Two versions of this system have been performed. The first iteration is described in Section 2.2, while the second one can be found in Section 2.3.. 2.1. Motivation. This radar originates from the need of a low cost CW-LFM radar to be used for educational purposes. The concept is based on a low-cost CW-LFM radar developed at MIT in [8], named Coffee-Can radar. The system described in the article uses connectorized RF components (VCO, splitter, mixer and amplifiers), an analog modulator to generate the voltage ramp to feed the VCO, and a laptop audio card to digitize the signal. The total bill of materials (BOM) of this design is about US360$. The RF components are a big portion of the total cost. A redesign of this system into a RF PCB is performed by engineers of AWR groups of National Instruments, detailed in [9], where the connectorized elements are replaced by discrete surface mount technology (SMT) components in an printed circuit board (PCB). This allows a US200$ reduction in the BOM cost. However, the sampling and ramp generation method are still the same. In this master thesis, a version of the PCB-based radar is developed and manufactured, looking to improve the already existing designs. This is achieved by using the same technology as the AWR group design: SMT components on a PCB. Additionally, the new selection of components decreases the BOM to US180$. Furthermore the ramp generation and sampling methods are not the same. A micro-controller is incorporated in the system. With built-in ADCs and DACs, this micro-controller allows on board sampling and ramp generation, becoming an autonomous system. The ADC has a higher sampling frequency than the PC sound card used in the MIT versions. Also, the DAC allows the generation of arbitrary waveforms, not only triangular. This incorporation does not have a big impact in the BOM, due to the reduced cost of the micro-controller. Additionally, a second iteration of this radar is performed. It fixes some faults and improves the overall system performance. A comparison between the existing system and the two versions of this radar can be seen in Table 2.1..

(34) Chapter 2. S band sensor. 6. Parameter. AWR group radar. First version the of S band radar. Second version of the S band radar. Units. Frequency band Range resolution Output power Sampling frequency Furthest detection Noise floor Dynamic range Complex baseband Power supply Cost. 2350 - 2550 75 22 44 45 No Batteries 320. 2250 - 2600 50 24 2000 80 -70 93 No USB 180. 1600 - 3200 10 20 2000 130 -70 93 Yes USB 250. MHz cm dBm KHz m dBm dB e/u. TABLE 2.1: Comparison between versions of the S band radar..

(35) 2.2. First version of the S band radar. 2.2. 7. First version of the S band radar. The first iteration of the radar based on the AWR group radar is described in this section. The proposed system is described bellow, and the selected components are detailed in Section 2.2.2. The designed and manufactured board can be seen in Section 2.2.3. This board is used for the characterization of each one of the components, shown in Section 2.2.4. Finally, the results of the complete system are discussed in Section 2.2.5.. 2.2.1. Proposed system. The built system is a CW-LFM radar manufactured on a FR4 PCB with SMT components. With a bandwidth of 360 MHz centered at 2.45 GHz, the system has a theoretical range resolution of 42 cm. Said bandwidth is the absolute maximum of the system, but can be configured to use any sub band of it. That is an important detail, because the bandwidth of the system is wider than the 100 MHz available at the 2.45 GHz ISM band. The system is powered, configured, and controlled via USB with a PC. Raw samples are transferred from the microcontroller at real time to the PC via serial port, which can be read from any serial monitor, such as the one incorporated in Matlab. Once in Matlab, samples can be processed (typically with a FFT) and plotted. Basic configuration of parameters, such as the ramp form, ramp duration or swept bandwidth, can be selected with the computer on the fly. The microcontroller is programmed in C. However, the system can be configured to operate as a doppler CW radar, by removing the frequency sweep. This allows the measuring the speed of the targets instead of the distance. No hardware modifications are needed. The system is configured from the PC and the processing script is adapted to doppler processing. The system can mount any desired antenna type, since it has SMA connectors for the transmission and reception. Usually, 3.15 dBi dipole antennas are used, due to the low cost and good performance in the band. The main disadvantage of using omnidirectional antennas is the increase of clutter when more than one isolated target is illuminated. As can be seen in Figure 2.1, the system is clearly divided into two subsystems: digital subsystem and analog subsystem. The digital subsystem has been designed, developed and coded by Luis Alberto Gómez, partner of the research group. While the analog subsystem has been developed and characterized by the author of this thesis. Since the digital subsystem is not the target of this master thesis but is necessary for the operation of the system, it is briefly described in Appendix E. The design and characterization of the analog subsystem is described along this section. In Figure 2.2 each functional block is marked and identified over the manufactured system. The analog subsystem is split into different functional blocks. Although every block is on the same PCB, each functional block is connectorized. This allows the isolation of each block and the detailed characterization of every component, without unwanted contributions from other elements of the system. The connection between blocks is made by SMA cables. In Figure 2.1 each functional block is delimited by a box, every SMA connection is marked with a thick arrow, while internal PCB connections via traces are marked with thin arrows, as indicated in the legend. Five functional blocks can be identified in the analog subsystem: RF signal generation, power amplification, low noise amplification, mixer and signal conditioning..

(36) Chapter 2. S band sensor. 8 DIGITAL SUBSYSTEM. ANALOG SUBSYSTEM COU PLE R. DAC. T X ANT EN NA. PA. VCO. RX ANT E NNA. µController. ADC. LPF. BB AMP. MIXER. LN A. SM A CABLE CO NE CT IO N. DAC: Dig ital to Analog Conv erte r. LN A: L ow N oise Amplifie r. LPF: Low Pas s Fi lter. IN TE RNAL PCB CO NE CTI ON. ADC: Anal og to Dig ital Conv erte r. PA: Powe r Amplifie r. BB AM P: Bas eBa nd Amplifie r. F IGURE 2.1: Architecture of the first version of the developed system. F IGURE 2.2: Photo of the manufactured PCB with the functional blocks identified.. The DAC of the microcontroller can be configured to generate any arbitrary waveform, although a sawtooth waveform is usually selected. The VCO is driven by the waveform of the DAC, oscillating at a frequency depending on the input voltage..

(37) 2.2. First version of the S band radar. 9. The power amplifier amplifies the generated signal, sending it to the transmitter antenna. A coupler following the amplifier is responsible for obtaining a sample of the transmitted signal to feed the mixer. The receiver antenna is connected to the LNA which is the input to the mixer’s RF port. Since the frequency difference of the received and the transmitted signal is reduced, the output signal of the mixer is baseband. It needs to be amplified and centered in the ADC’s voltage range, which is accomplished with operational amplifiers. Also, it is low pass filtered to avoid aliasing. The amplified and filtered signal is sampled by the ADC. The overall cost of the first version of the S band radar is below 200 e. A detailed view of the components costs can be seen in Table F.1 of Appendix F.. 2.2.2. Component selection. In this subsection, the selected components for the first design of the S band radar is presented. Limiting factors, theoretical performance, costs and other factors are explained, helping to understand the selection process and the final decisions. As said before, one of the main reasons to select an operation band centered in 2.45 GHz is because of the wide component availability due to the existence of commercial communication systems (WIFI or Bluetooth). Also, the MIT Coffee-Can radar proves that said band can be used for the desired purposes. The high popularity and demand of communications systems at S band results in a high offer in components, which leads to reduced prices. Amplifiers and mixers can be easily found, with several alternatives. WIFI antennas can be used for the system as a fast and cheap alternative, in spite of the lack of directivity. Multiple VCOs can be found working in the desired band, but it is the most band-restricted component. Whilst several amplifiers and mixers operate in a very wide band (wider than WIFI band), most VCOs are restricted to the WIFI band, about 100 MHz. Also, the power source of this design offers an important limiting factor. Since the board is USB powered, it is restricted to 5 V and 1 A. The USB standard specifies a limit of 500 mA per USB port, but most computers can handle 1 A. Even so, amperage is not the limiting factor, since it can be bypassed by using more than one USB port. By connecting two ports in parallel, the maximum current is doubled and any computer with two USB ports can supply at least 1 A. For this reason, the board is equipped with two USB ports for power. The second USB port has never been needed, reinforcing the previous statement affirming than most of the computers can handle 1 A per USB port. However, the limiting factor is the voltage. The higher available voltage is 5 V, and cannot be easily sorted out. Two alternatives are proposed: implementation of DC to DC converters generating the needed voltage or using components that can be powered with 5 V or less. The first one is attractive, since a lot of components require more than 5 V (12, 36 or even 40 V are typical in radar systems). Particularly VCOs and PAs. But DC to DC converters can be noisy [10]. Especially in frequencies up to a few MHz, affecting the baseband frequency. Also, noise coupled to the VCO ramp is translated into phase noise of the RF signal. The other alternative, limiting the component search to a power supply limit of 5 V reduces components spectrum. However, low voltage devices are typically used in consumer electronics such as computers or mobile devices, with low power and frequency requirements. Finally, the second option is selected, since capable components are found operating at less than 5 V and this option offers lower noise. No DC-to-DC converter.

(38) Chapter 2. S band sensor. 10. is used in this first design. Every selected device is powered at 3.3 V, so linear low drop-out regulators (linear LDOs) are used to reduce the voltage from 5 to 3.3 V. LDOs are known for introducing less noise than switching regulators, at the expense of dissipating more power. Since the consumption of the board has to be less than 1 A and the voltage drop of the regulators is less than 1.7 V, the dissipated power is lower than 1.7 W, which most LDOs can hold. With the limitations explained, a list of each selected component is described. Also, a brief description, with the main characteristics of the components, is presented. • The selected VCO is the model MAX2750 from MAXIM, a self-contained integrated circuit (IC) matched to 50 Ω. Its datasheet can be seen in [11]. Although it is intended for use in the 2.4 to 2.5 GHz band, it can generate frequencies from 2.25 GHz to 2.6 GHz when the tuning voltage variates from 0 to 3.3 V. This is a great advantage since the DAC has the same voltage range, so there is no need for an amplification stage that would be required if the tuning range of the VCO were greater than the DAC range. This VCO is one of the few VCOs available from the main suppliers F IGURE 2.3: with said requirements (bandwidth broader than 100 Photo of the MHz and tuning voltage from 0 to 3.3 V). Also, its mounted VCO. output power of -3 dBm is appropriate for driving the power amplifier. • For the PA, the model SKY65006 from SKYWORKS is chosen. The datasheet of said component can be seen in [12]. As happens with the VCO, the intended band of use is from 2.4 to 2.5 GHz, but it can handle wider bandwidth. With a gain of 27 dB and a saturation output power of 24 dBm, the output power of the VCO drives the PA into saturation. Also, the specified gain 2.4: Photo variation over frequency is only 0.2 dB.. F IGURE of the mounted PA.. • Model CP0302 from AVX is chosen as coupler. Its datasheet can be seen in [13]. It is chosen because of the frequency range of operation and the coupling factor of -20 dB. With the output power of the PA, this coupling factor gives the necessary power to the local oscillator port of the mixer.. F IGURE 2.5: Photo of the mounted coupler..

(39) 2.2. First version of the S band radar. F IGURE 2.6: Photo of the mounted LNA.. • The model QPL9065 from QORVO is used as LNA. The complete characteristics of the component can be seen in [14]. It is composed of two concatenated amplifiers, with 17 and 15 dB of gain respectively. Each amplifier can be bypassed, allowing three states: OFF, low-gain mode and high-gain mode. This IC works from 450 MHz to 3.8 GHz, which includes the working band. The noise figure is about 0.6 dB.. • The selected mixer is the ADL5350 model from Analog Devices. The datasheet can be found in [15]. The RF and local oscillator (LO) ports can be connected to signals up to 4 GHz. The intermediate frequency (IF) port is DC coupled. The conversion loss can be as high as 7 dB, which will be compensated with the following stage of amplifiers.. F IGURE 2.8: Photo of the conditioning stage.. 11. F IGURE 2.7: Photo of the mounted mixer.. • The signal conditioning stage is composed of operational amplifiers. The selected model is OPA2354 from Texas Instruments. Its datasheet can be found in [16]. It is selected due to the rail-to-rail operation and the low noise contribution. Also, it reaches higher frequencies than most operational amplifiers, up to 100 MHz.. • Finally, the selected microcontroller (µC) is the STM32F205VET6 model from ST, and its datasheet can be found at [17]. The design and operation of the digital part is not part of this master thesis. This µC has three 12-bit ADCs with up to 2 MSPS each. Additionally it includes two 12-bit DACs with up to 1 MSPS of sampling frequency. The total memory of the µC is 1 MByte. The board containing the system is a PCB of 150x70 mm of FR4, with a dielectric constant (er ) of 4.7. It is manufactured by EuroCircuits, an European company capable of fulfilling the design requirements and with affordable prices. The board is composed of a stack-up of 4 copper layers. The buildup can be seen in Figure 2.9. Outer layers of copper have a thickness of 18 µm, while the inner layers thickness is 35 µm. Also, the separation between inner layers is 0.71 mm and between inner and outer layer is 0.36 mm. On the top and the bottom layers, the copper is covered by solder mask and the correspondent silkscreen.. 2.2.3. Board layout. Each selected component provides a recommended schematic connection as well as a recommended layout distribution, and both were followed when possible. Almost all components are isolated with theirs inputs and outputs connectorized. The component distribution along the board is determined by the connections needed between the components, optimizing the cables distribution. The manufactured top.

(40) Chapter 2. S band sensor. 12. F IGURE 2.9: Buildup of EuroCircuits 4 layers PCB. layout can be in Figure 2.10. The upper components correspond to the analog section, while the lower are the digital section. For full documentation, Appendices D.1.1 and D.1.2 has the complete schematics and layouts of this board. COJ2. COJ10. PAJ203 PAJ205 COU3. COL4 PAL401 PAJ201. PAC1601PAC1602. PAL402. COC16. PAJ202 PAJ204. COC6 COL2. COC4 COC5. PAC602 PAL201 PAC601 PAL202. PAC5902 PAC501 PAC5302 PAC802 PAC4302 PAC6202 PAC5602 PAC6602 PAC3202 PAC3702 PAC3602 PAC3502 PAC4102 PAC4602 PAC5802 PAC5702 PAC5502 PAC402 PAC202 PAC3302 PAC3902 PAC3802 PAC4202 PAC4402 PAC4702 PAC6402 PAC102 PAC302 PAC1302 PAC3402 PAC4802 PAC6102 PAC6002 PAC6502 PAC4502. COC10. PAC1502. COC1 PAC1501. COC62. COC8. PAJ103 PAJ105. PAC6201 PAC6202. PAC801 PAR3001 PAC802 PAR3002. PAJ101. PAC7101 PAC7102. COC15. COJ1. PAU1404 PAU1405 PAU1406. PAU1403 PAU1402 PAU1401. PAU1407. PAU504. PAU506. PAU503. PAU507. PAU502. PAU508. PAU501. COC71. COR30. PAU401 PAU404 PAU402 PAU403. PAJ1001 PAR402PAR401. COR4. PAC7201 PAC7302 PAC7202 PAC7301. PAJ1003 PAJ1005. COC72. COC74COC73. PAC7401. PAU505. COU4. COC14 PAC1201 COU14 PAC1202. PAC1101 PAR501PAR502. COR5. PAJ1002 PAJ1004. COC7 PAC502 PAC6501 PAL102 COL1 PAC401 PAC201 PAC4401 PAC6401 PAC3301 PAC3901 PAC3801 PAC4201 PAC4701 PAC801 PAC1301 PAC3201 PAC3701 PAC3601 PAC3501 PAC3401 PAC4101 PAC4301 PAC4601 PAC4501 PAC4801 PAC5301 PAC6201 PAC6101 PAC6001 PAC5901 PAC5801 PAC5701 PAC5601 PAC5501 PAC6601 PAC101 PAU3016 PAU3015PAU3014PAU3013PAU3012 PAC301 PAU3011 PAC701PAC702PAL101 PAC902 PAL301 PAL302 PAC1002 PAU3017PAU3010 PAU309 PAC901 COL3PAC1001 PAU305 PAU306PAU307PAU308 PPAACC11440021 PAR602 PAR601 COC9 PAR301 PAR302 PAC1102 COR3 COC12 COR6 PAU301 PAU302 PAU303 PAU304. PAC7402. COJ8. PAJ802 PAJ804. COC13 PAC1302 PAC1301. PAJ801. COU5 PAR2902. COR29. PAJ102 PAJ104. PAR2901. PAC7002 PAC7001 COC70. PAJ803 PAJ805 COR10. COJ5. PAJ503 PAJ505. COR22. PAR1001 PAR1002. COC26 PAC2602 PAC2601. PAR902 PAR901 PAC2501PAC2502 PAR2002 PAR2001. COR9. COC30 PAR2201 COR21 PAC30 1 PAC3002 PAR2202 PAR2102 PAR2101. PAJ501. COJ11 COC25. PAJ102 PAJ104 PAJ202 PAJ204 PAJ402 PAJ404 PAJ502 PAJ504 PAJ702 PAJ704 PAJ802 PAJ804 PAJ1002 PAJ1004 PAJ1102 PAJ1104 PAJ1202 PAJ1204 PAJ1302 PAJ1304. COR20. PAU608PAU607PAU606PAU605. PAU6017. PAU609 PAU6010 PAU6011 PAU6012. PAU604 PAU603 PAU602 PAU601. COC28 PAL501PPAL801PAL901AL10 1 COL9. PAC1101 PAC1001 PAC901 PAC1501 PAC1801 PAC2101 PAC2401 PAC3101 PAC7301 PAC3001 PAC2901 PAC1901 PAC2201 PAC2301 PAC6301 PAC2501 PAC2601 PAC2701 PAC2801 PAC6701 PAC2802 PAC2801 PPAL902 PAL502 PAL802 AL10 2 PAL902 PAL901 PAC6702 PAC1002 PAC1102 PAC1802 PAC7302 PAC3102 PAC1902 PAC2202 PAC2602 PAC2502 PAC6302 PAC902 PAC1502 PAC2102 PAC2402 PAC2302 PAC2702 PAC2802 PAC2902 PAC3002. PAU6013PAU6014PAU6015PAU6016. PAJ1101 PAJ1001 PAJ801 PAJ701 PAJ501 PAJ1301 PAJ401 PAJ1201 PAJ201 PAJ101. COC31. COL11. COU6. COL6 PAL601 PAL501PAL502 COL5. PAJ502 PAJ504. PAL602. COC21. COC19. PAR701. PAC6801 PAC6802 PAC2001 PAC1701 PAC5001 PAC5201 PAC6901 PAC6902 PAC5202 PAC5002 PAC1702 PAC2002 COC17. PAJ103 PAJ105 PAJ203 PAJ205 PAJ403 PAJ405 PAJ503 PAJ505 PAJ703 PAJ705 PAJ803 PAJ805 PAJ1003 PAJ1005 PAJ1103 PAJ1105 PAJ1203 PAJ1205 PAJ1303 PAJ1305. COC22 COC24. PAC2201PAC2202. PAC2101 PAC2102 PAC2402PAC2401 PAC1902 PAC1901. PAR802 PAR801. COR8. PAR702. COR7. COJ4 COJ13. PAJ403 PAJ405. PAJ1302 PAJ1304. COL12 PAL1201PAL1202COC27 PAC2701. PAJ401. PAC2702. PAU708. PAU702. PAU707. PAU703 PAU704. PAU706 PAU705. COL10PAL1001PAL1002 PAU709. PAJ402 PAJ404. COC23. COU7 PAU701. PAC2301 PAC2302 COL8 COC63 PAL801 PAL802 PAC6301 PAC6302 PAL1201 PAL701 PAL702 PAL1202. COC29PAC2901PAC2902. PAJ1301. COL7. PAC1801PAC1802. PAJ1303 PAJ1305. COC18. PAC2002 PAC2001 COC20. COJ12. PAJ1203 PAJ1205. COU13. COC69. PAC6901 PAC6902. PAJ1201. PAC6501. COC3 PAR2302 PAC6502 PAC302. COTP1 COSTLINK. PAR2301. PAC301. PATCP1201. PAU104. PAU106. PAU103 PAU102. PAU108. PAR2401. PAU101. PAR2402. PAR202 PAR201 COR2. COC2 PAC202 PAC201. COR24 COC67. PAR2502. COC68. COJ7. PAJ702 PAJ704 PAJ701. COU2. PAC6701 PAC6702. COC66 PAU201. PATP201. PAU2010. PAU202. PAU209. PAU203 PAU204 PAU205. PAU208 PAU207 PAU206. PAJ703 PAJ705. PAC6602 PAC6601. COTP2. COC37 COC33 COC34. PASTLINK03. PAC3701 PAC3702 PAC3302. PASTLINK04. PAC3402. COJ3. PAC3301 PAC3401. PAJ301. PAU8076 PAU8075 PAU8077 PAU8074 PAU8078 PAU8073 PAU8079 PAU8072 PAU8080 PAU8071 PAU8081 PAU8070 PAU8082 PAU8069 PAU8083 PAU8068 PAU8084 PAU8067 PAU8085 PAU8066 PAU8086 PAU8065 PAR1102 PAU8087 PAU8064 PAU8088 PAU8063 PAU8089 PAU8062 PAU8090 PAU8061 PAU8091 PAU8060 PAC3602 PAR1101PAU8094 PAU8092 PAU8059 PAU8093 PAU8058 PAU8057 PAU8095 PAU8056 PAC3601 PAC3202 PAU8096 PAU8055 PAU8097 PAU8054 PAU8098 PAU8053 PAU8052 PAU8051 COC36 PAC3201 PAU80100PAU8099 COC32 COU8 PAU801 PAU8050 PAC4602PAC3502PAC3501 PAU802 PAU8049 PAU803 PAU8048 PAU804 PAU8047 PAU8046 PAU806 PAU8045 PAU807 PAU8044 PAC4001 PAU805 PAU808 PAU8043 PAC4802PAC4801PAC4601 COC35 PAU8042 PAU8010 PAU8041 PAU8011 PAU8040 COC46 PAC4002 PAC3901 PAU809 PAU8012 PAU8039 PAU8013 PAU8038 PAU8014 PAU8037 PAU8015 PAU8036 COC48 COC40 PAC3902PAC3802PAC3801PAU903 PAU8035 PAU8017 PAU8034 PAU8018 PAU8033 PAU1503 COU9PAU8016 PAU8019PAU8021 PAU8032 PAU8031 COC39 PAU1504 PAU8030 PAU902 PAU8020 PAU1502 PAU8022 PAU8029 PAU8023 PAU8028 COC38PAC4101PAU904PAU1501 PAU8024 PAU8027 PAC4201 PAU8025 PAU8026 PAU901 PAC4701 COC47 PAC4102 PAC4202 PAC4302 PAC4702 COC41 COC42 PAC4301PAC4402PAC4401 COC43. PASTLINK05 PASTLINK06. PAJ302. COR11. CORST1. PARST102 PAR1201 PAR1202. PARST101. COR12. PAC4502 PAC4501 COC45. COC44. COFB3. COFB2. PAC5502 COC52 COU10 PAFB202 PAC5201. PAFB2302 PAFB3201 PAFB201 PAC5202 PAU1009 PAU1001. PAU1008. PAU1002. PAU1007. PAU1003. PAU1006. PAU1004. PAU1005. PAC5602 PAC5601 COC56 COUSB0POWER COR13. COD1. PAR1302 PAD101 PAR1301. PAD102. PAUSB0POWER06. COR17. COC58. PAU1208PAU1207PAU1206PAU1205PAU1204PAU1203PAU1202PAU1201. PAC5501. PACN0103. PAR1702 PAR1701. COU12. COC55. COCN01. PACN0101. PAC6802 PAC6801. PAR101 COC1 PAC102 PAC101. COU1. PAU105 PAU107. PASTLINK02. PACN0102. PAU1303 PAU1302 PAU1301. PAR102. COC65. COC64 PAC6402 PAC6401. COR25 PAR2501. PASTLINK01. PAU1305. COR1. COR23. PAJ1202 PAJ1204. PAU1304. PAUSB0POWER01PAUSB0POWER02PAUSB0POWER03PAUSB0POWER04PAUSB0POWER05. COR18 COR19. PAR1802 PAR1801 PAR1902 PAR1901. PAU1209 PAU12010 PAU12011 PAU12012 PAU12013 PAU12014 PAU12015 PAU12016. PAU12033. PAU12032 PAU12031 PAU12030 PAU12029 PAU12028 PAU12027 PAU12026 PAU12025. PAU12017PAU12018PAU12019PAU120 PAU120 1PAU120 2PAU120 3PAU120 4. COC50 PAC5002 PAC5001. COC61. PAC5802 PAC5801. PAUSB0DAT 01PAUSB0DAT02PAUSB0DAT 03PAUSB0DAT04PAUSB0DAT 05. COR28 PAR2802 PAR2801. PAD401 PAD402 COD4. PAR1401. PAU1503 PAU1502 PAC7501 PAU1504 PAU1501 PAC7502. PAC1601 PAR2601 PAL201 PAR801 PAR1001 PAC501 PAC1401 PAL401 PAR601 PAR401 PAR2201 PAR2501 PAC601 PAC701 PAL301 PAL101 PAR501 PAR701 PAR901 PAR2801 PAR2701 PAR2601 PAR301 PAR1701 PAR1801 PAR1901 PAR2001 PAR2101 PAR3101 PAR502 PAR2602 PAR302 PAC502 PAL102 PAR702 PAR902 PAR2502 PAR1902 PAR1802 PAR1702 PAC602 PAR2802 PAR2602 PAR2702 PAL202 PAC702 PAL402 PAC1602 PAR802 PAR2002 PAR1002 PAR2202 PAR2102 PAR402 PAR3102 PAR602 PAC1402 PAL302. COJ6 PAU1104 PAU1105. COU11. COC75 COR14 COC57COR16COC60. COD2 COR15 PAD202 PAR1501 PAD102 PAD101 PAR1502 PAD201. PAD403 PAD404. COR27 COR26. PAU1103 PAU1102 PAU1101. PAC5401. PAC5402. PAR3102 PAR3101. PAC4901 PAC5101. PAUSB0DATA06. PAJ304. COC59 COC53. COR31 PAC5901 PAC5301 PAC5902 PAC5302. PAC6102 PAC5702 PAR1201 PAR101 PAC6002 PAR1402 PAR2301 PAR2401 PAR201 PAR1301 PAR1501 PAR1101 PAR1401 PAR1601 PAC5102PAC5101 COC51 COU15 PAR102 PAC6001 PAR1202 PAR1402 PAR1302 PAR1102 PAR202 PAR2302 PAR2402 PAR1502 PAC6101 PAC5701 PAR1602 PAFB102 COFB1 PAFB102 PAFB101 PAFB402 PAFB401 PAD302 PAD301 COD3 COUSB0DATA COFB4 PAFB101 PAC4902 PAC5102. COC49. PAJ303. COC54. PAJ603 PAJ602 PAJ601 COCN0GND. PACN0GND02 PACN0GND01. F IGURE 2.10: Layout of the first version of S band radar..

(41) 2.2. First version of the S band radar. 13. Since the wavelength for the working frequency is about 12 cm and the board has dimensions of the same range, the tracks of the PCB can be modeled as a transmission line. Thus, special attention has to be given to the line impedance. In the selected PCB build up, explained in Section 2.2.2, the RF signals are routed only using the upper layer and the following layer is a ground plane. With this configuration, the equivalent transmission line model is a microstrip line. More information about microstrip lines can be found in Section 3.8 of [18]. In communications the most used line impedance is 50 Ω, and every RF component in the developed board is matched to said impedance. As it is specified in Equation 2.1 (Equation 3.197 of [18]), the impedance of a microstrip line is determined by the er of the dielectric, the distance between both conductors (signal conductor and ground plane) and the width of the signal conductor. Since the thickness and the er are fixed, the only variable remaining is the width of the track. Following said equations, the theoretical needed width of the PCB tracks for a 50 Ω line impedance is 0.65 mm. W = d. (. 8e2 e2A −2 2 π [ B − 1 − ln (2B. for. − 1) +. er − 1 2er { ln ( B. − 1) + 0.39 −. 0.61 er }]. for. W d W d. <2 >2. (2.1). However, before manufacturing, all the tracks were electromagnetically simulated with Momentum ADS, by importing the designed layout. The S parameters of each one were studied, searching for a good 50 Ω matching at 2.45 GHz. The simulation shows good matching for all the tracks, corroborating the theoretical values.. 2.2.4. Component characterization. In this subsection, the characterization of the manufactured system is described. Relevant parameters of each component are measured. Most of the components are measured isolated, thanks to the connectorized layout. However, blocks are connected when needed for some measurements. 2.2.4.1. VCO. As said before, the VCO is the model MAX2750. The most relevant characteristics as the datasheet specifies can be found in Table 2.2. Parameter. Typ. Unit. Oscillator Guaranteed Frequency Limits Phase noise @ 4 MHz Output Power Tuning gain @ 2400 MHz Tuning gain @ 2500 MHz Harmonics Icc. 2400 - 2500 -125 -3 140 90 -30 14. MHz dBc/Hz dBm MHz/V MHz/V dBc mA. TABLE 2.2: VCO datasheet parameters.. Tuning curve The tuning curve of the VCO is the variation of the output frequency along the input voltage. The VCO tuning curve is usually non-linear. This effect is important.