Design of a printed antenna for a communication system working at C band for unmanned aerial vehicles.

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(1)GRADO EN INGENIERÍA DE TECNOLOGÍAS Y SERVICIOS DE TELECOMUNICACIÓN TRABAJO FIN DE GRADO. DESIGN OF A PRINTED ANTENNA FOR A COMMUNICATION SYSTEM WORKING AT C BAND FOR UNMANNED AERIAL VEHICLES. XIAOLIANG SUN 2016.

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(4) GRADO EN INGENIERÍA DE TECNOLOGÍAS Y SERVICIOS DE TELECOMUNICACIÓN. TRABAJO FIN DE GRADO Título:. DESIGN OF A PRINTED ANTENNA FOR A COMMUNICATION SYSTEM WORKING AT C BAND FOR UNMANNED AERIAL VEHICLES. Autor:. Don Xiaoliang Sun. Tutor:. Don José Manuel Fernández González. Departamento:. Señales, Sistemas y Radiocomunicaciones. MIEMBROS DEL TRIBUNAL Presidente:. Don Mateo Burgos García. Vocal:. Don Manuel Sierra Castañer. Secretario:. Don Valentín de la Rubia Hernández. Suplente:. Doña Belén Galocha Iragüen. Los miembros del tribunal arriba nombrados acuerdan otorgar la calificación de: ………. Madrid, a 12 de Julio. de 2016.


(6) UNIVERSIDAD POLITÉCNICA DE MADRID ESCUELA TÉCNICA SUPERIOR DE INGENIEROS DE TELECOMUNICACIÓN. GRADO EN INGENIERÍA DE TECNOLOGÍAS Y SERVICIOS DE TELECOMUNICACIÓN TRABAJO FIN DE GRADO. DESIGN OF A PRINTED ANTENNA FOR A COMMUNICATION SYSTEM WORKING AT C BAND FOR UNMANNED AERIAL VEHICLES. XIAOLIANG SUN 2016.

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(9) RESUMEN Actualmente la autonomía de los UAVs(vehículos aéreo no tripulado) está limitada por los enlaces de comunicaciones, tanto para garantizar la posibilidad de telecomando, como para tener la capacidad de enviar la información captada por sus sensores a una estación de control terrena. La solución es realizar un enlace de larga distancia, con alta calidad de servicio, multicanal, con un ancho de banda moderado y precio asumible. El punto clave del sistema de comunicaciones UAV es el sistema radiante. En este trabajo se propone el estudio, diseño e implementación de una antena impresa que consiste en una agrupación cilíndrica de elementos radiantes circulares. Esta antena sirve para transmitir datos de control y videos en los dos tramos de enlaces UAV-UAV y UAV- estación terrena La tecnología de circuitos impresos permite la fabricación de elementos radiantes a gran escala y bajo coste, con una gran facilidad de integración en sistemas de comunicaciones. Además, propicia la construcción de agrupaciones de varias antenas, que cuentan con mayores prestaciones que los elementos unitarios. Estas agrupaciones permiten satisfacer con mayor completitud las necesidades del sistema, pues cuentan con una gran versatilidad. Sin embargo a pesar de sus múltiples ventajas también presentan algunos inconvenientes, como por ejemplo el acoplo mutuo que aparece entre las mismas cuando forman parte de un array.. SUMMARY Currently the autonomy of UAVs(Unmanned Aerial Vehicles) is limited by communication links, both to ensure the possibility of remote control, to be able to have capacity for sending the information captured by its sensors to an earth station control. The solution is to make a long distance link with high quality service, multichannel, with a moderate bandwidth and acceptable price. The key point of the communications system UAV is the radiating system. This work proposes the study, design and implementation of a printed antenna consisting in a cylindrical array of circular radiating elements in C band. This antenna is used to transmit control data and videos in two sections of links: UAV-UAV and UAV-ground station. The printed circuit technology enables the manufacture of radiating elements on a large scale and low cost, with great ease of integration into communication systems. Furthermore, it encourages the construction of array antennas, which have higher performance than unitary elements. These arrays allow more completeness to achieve the system requirements, as they have great versatility. Yet despite its many advantages, also they have some drawbacks, such as the mutual coupling that appears between them when they are part of an array.. PALABRAS CLAVE Antena , , parche circular , array cilíndrico , , polarización lineal , polarización circular, diagrama de radiación , ganancia , directividad, ancho de haz , banda C , FR4 , FOAM , material, estructura multicapa , coaxial , microstrip , SMA , acoplo , combinación , aislamiento , transmisor , receptor , omnidireccional , substrato , plano de masa , adaptación , UAV , avión , telemetría , datos , control , agrupación, espesor, alimentación, adaptación .. KEYWORDS Antenna , patch , microstrip , polarization , radiation pattern , gain , directivity , beamwidth , isolation , coupling , cylinder array , UAV , telemetry, adaptation, data, control, video , transmitter, receiver , ground plane.


(11) ÍNDICE DEL CONTENIDO 1.. INTRODUCTION AND OBJECTIVES.......................................................................................... 1 1.1. INTRODUCTION ....................................................................................................................... 1 1.2. OBJECTIVES ............................................................................................................................. 2. 2.. THEORY OF MICROSTRIP ANTENNAS ..................................................................................... 3 2.1. INTRODUCTION ....................................................................................................................... 3 2.2. BASIC CHARACTERISTICS ......................................................................................................... 3 2.2.1. Basic Properties ............................................................................................................... 3 2.2.2. Surface Waves ................................................................................................................. 5 2.2.3. Fringing Fields ................................................................................................................. 5 2.3. FEEDING METHODS ................................................................................................................. 6. 3.. DESIGN OF A CIRCULAR MICROSTRIP PATCH ANTENNA ......................................................... 9 3.1. SYSTEM SPECIFICATIONS......................................................................................................... 9 3.2. FRECUENCY SELECTION AND SUBSTRATE PARAMETERS......................................................... 9 3.3. DESIGN OF PATCH ................................................................................................................. 10 3.3.1. Design Procedure .......................................................................................................... 11 3.3.2. Selection Of Polarization ............................................................................................... 12 3.3.3. Design of Microstrip Transmission Line ........................................................................ 13. 4.. DESIGN OF CYLINDER ARRAY ANTENNAS ............................................................................. 17 4.1. ARRAY ANTENNA CHARACTERISTICS..................................................................................... 17 4.1.1. Array Factor .................................................................................................................. 17 4.1.2. Array Pattern................................................................................................................. 17 4.1.3. Main Lobe and Sidelobe Levels ..................................................................................... 18 4.1.4. Element Spacing ............................................................................................................ 18 4.1.5. Grating Lobes ................................................................................................................ 18 4.2. RADIUS OF THE CYLINDER ..................................................................................................... 19 4.3. ARRAY CONFIGURATION ....................................................................................................... 20 4.3.1. Cylinder Array With Eight Elements .............................................................................. 21 4.3.2. Cylinder Array With Sixteen Elements ........................................................................... 22. 5.. ANTENNA SIMULATIONS..................................................................................................... 24 5.1. SIMULATION OF A LINEAR POLARIZATION PATCH ANTENNA ..................................................... 24 5.2. SIMULATION OF CIRCULAR POLARIZATION........................................................................... 25 5.2.1. Simulation Of Circular Polarization With Ideal Ports .................................................... 25 5.2.2. Simulation Of 3dB Microstrip T-Junction Power Divider ............................................... 27 5.2.3. Simulation Of Patch with 3dB Microstrip T-Junction Power Divider ............................. 28 5.3. STUDY OF NUMBER OF RADIATING ELEMENTS ..................................................................... 29 5.4. STUDY ON THE INFLUENCE OF GROUND PLANE.................................................................... 31 5.5. CYLINDER ARRAY USING SIXTEEN ELEMENTS FOR TRANSMISSION AND RECEPTION ............. 32 5.5.1. Simulation of Combination Of Four Radiating Elements............................................... 32 5.6. CYLINDER ARRAY USING EIGHT ELEMENTS FOR TRANSMISSION AND EIGHT ELEMENTS FOR RECEPTION ........................................................................................................................................ 34 5.6.1. Isolation Between Transmitter And Receiver ................................................................ 35 5.6.2. Combination Of Two Elements ...................................................................................... 35 5.6.3. Modifications In the Design to Improve The Isolation .................................................. 36 5.6.4. Combination Of Two Elements ...................................................................................... 38 5.7. COMPLETE STUCTURE ........................................................................................................... 39 5.7.1. Simulation En CST Studio............................................................................................... 39 5.7.2. Simulation In Matlab..................................................................................................... 41.

(12) 6.. REAL ANTENNAS MEASUREMENTS ...................................................................................... 43 6.1. FABRICATION PROCESS ......................................................................................................... 43 6.2. REAL PATCH ANTENNAS MEASUREMENTS............................................................................ 44. 7.. CONCLUSION AND FUTURE WORK ...................................................................................... 49 7.1. CONCLUSIONS ........................................................................................................................... 49 7.2. FUTURE WORK ...................................................................................................................... 49. 8.. PUBLICATIONS .................................................................................................................... 50. 9.. REFERENCES ....................................................................................................................... 51.

(13) ÍNDICE DE TABLAS Table 3.1.1 Antenna Performances. ........................................................................................................ 9 Table 3.2.1 Characteristics Of Substrate. .............................................................................................. 10 Table 3.3.1 Tabulated Comparison for the Determination Of Microstrip Power Divider Lines Width Of Zo= 50 Ω. ......................................................................................................................................... 15 Table 3.3.2 Tabulated Comparison For The Determination Of Microstrip Power Divider Lines Width Of Z_λg= 35 Ω. ..................................................................................................................................... 16 Table 4.2.1 Comparison Of Different Configuration Of Cylinder Array. ............................................ 20 Table 6.2.1 Gain Comparison Table. .................................................................................................... 48 Table 6.2.2 Beamwidth Comparison Table. ......................................................................................... 48. ÍNDICE DE GRÁFICAS Figure 1.1.1 Long-Range UAV-Relay System. ...................................................................................... 1 Figure 2.2.1 Typical Geometry Of a Microstrip Antenna. ...................................................................... 3 Figure 2.2.2 Typical Shapes Of Patch..................................................................................................... 4 Figure 2.2.3 Different Types Of Waves In a Microstrip Patch Antenna. ............................................... 5 Figure 2.2.4 Electric Field In a Microstrip Antenna. .............................................................................. 6 Figure 2.2.5 A Microstrip Patch Antenna Showing Fringing Fields. ..................................................... 6 Figure 2.3.1 Microstrip Line Configuration Using a Direct Approach. .................................................. 7 Figure 2.3.2 : Probe Fed Configuration Using a Direct Contact Approach. ........................................... 7 Figure 2.3.3 Aperture-coupled (left) And Proximity-coupled (right) Configuration Using a Noncontacting approach. ............................................................................................................................... 8 Figure 2.3.4 A Patch Excited Using a Coaxial Probe. ............................................................................ 8 Figure 3.2.1 Structure Of The Designed Patch Antenna. ...................................................................... 10 Figure 3.3.1 Example Of Lineal Polarization And Example Of Dual Polarization By Excitation Through Two Suitable Orthogonal Different Feed Points. ................................................................... 12 Figure 3.3.2 Structure With Microstrip Line. ....................................................................................... 13 Figure 3.3.3 Equivalent Circuit. ............................................................................................................ 13 Figure 3.3.4 3dB Microstrip T-Junction Power Divider. ...................................................................... 14 Figure 3.3.5 Feeds Points (Side). .......................................................................................................... 14 Figure 3.3.6 Feeds Points (TOP)........................................................................................................... 14 Figure 3.3.7 Macro Option CST Microwave Studio Suite.................................................................... 15 Figure 3.3.8 Structure Of a Microstrip Line. ........................................................................................ 15 Figure 3.3.9 The Corners In Microstrip Line Have To Be Cut To Preserve a Constant Impedance. ... 16 Figure 4.1.1 A Typical Example Of Grating Lobes Resembling The Main Lobe. ............................... 18 Figure 4.2.1 Structure between Two Consecutive Elements. ............................................................... 19 Figure 4.3.1 Cylinder Array With Eight Radiating Elements. .............................................................. 21 Figure 4.3.2 System Architecture Using Eight Elements. .................................................................... 21 Figure 4.3.3 Cylinder Array With 16 Radiating Elements. ................................................................... 22 Figure 4.3.4 Diagram Of Transmission And Reception Using Sixteen Elements. ............................... 22 Figure 4.3.5 Structure With 16 Radiating Elements Without Shifters. ................................................. 23 Figure 5.1.1 Circular Patch Design With Lineal Polarization. ............................................................. 24 Figure 5.1.2 Parameter S11 (a) and Smith Chart (b)............................................................................. 24 Figure 5.2.1 Patch With Circular Polarization And Sweep Of The Radius. ......................................... 25 Figure 5.2.2 Parameter S11 (a) and Smith Chart (b)............................................................................. 25 Figure 5.2.3 Radiation Pattern In Azimuth (a) And Elevation(b). ........................................................ 26 Figure 5.2.4 Radiation Pattern In Azimuth (a) And Elevation(b). ........................................................ 26 Figure 5.2.5 Axial Ratio In Azimuth (a) And Elevation (b). ................................................................ 26 Figure 5.2.6 Relation Polar(Red)-Contrapolar (Green). ....................................................................... 27 Figure 5.2.7 Design Of 3dB Microstrip T-Junction Power Divider...................................................... 27 Figure 5.2.8 Scatting Parameters In Magnitudes (a) And Phase (b). .................................................... 28.

(14) Figure 5.2.9 Patch Design With Microstrip Line Feeding. ................................................................... 28 Figure 5.2.10 Parameter S11 (a) and Smith Chart (b)........................................................................... 28 Figure 5.2.11 Axial Ratio In Azimuth (a) And Elevation (b). .............................................................. 29 Figure 5.2.12 Radiation Pattern en 3D. ................................................................................................. 29 Figure 5.3.1 Design of A Simple Patch (a) And Two Patches (b). ....................................................... 29 Figure 5.3.2 Radiation Pattern In Azimuth (a) And Elevation (b) Of Simple Patch. ........................... 30 Figure 5.3.3 Radiation Pattern In Azimuth (Left) And Elevation (Right) Of Two Patches. ................ 30 Figure 5.4.1 Patch Design With Different Ground Plane 36x36 mm (a) 60x60 mm (b). ..................... 31 Figure 5.4.2 Radiation Pattern In 3D with Ground Plane 60 x 60 mm. ................................................ 31 Figure 5.4.3 Radiation Pattern In Azimuth (a) And Elevation (b). ....................................................... 31 Figure 5.5.1 Structure of Cylinder Array With Sixteen Elements. ....................................................... 32 Figure 5.5.2 Parameter S11 (a) and Smith Chart (b)............................................................................. 32 Figure 5.5.3 Radiation Pattern En 3D. .................................................................................................. 33 Figure 5.5.4 Radiation Pattern In Azimuth (a) And Elevation(b) In Polar. .......................................... 33 Figure 5.5.5 Radiation Pattern In Azimuth (a) And Elevation(b) In Cartesian. ................................... 33 Figure 5.5.6 Axial Ratio In Azimuth (a) And Elevation(b). ................................................................. 34 Figure 5.5.7 Relation Polar (Red) and Contrapolar (Green). ................................................................ 34 Figure 5.6.1 Structure Of Design For 8 Elements. ................................................................................ 34 Figure 5.6.2 1 Isolation Between Channels In Transmission or Reception. ......................................... 35 Figure 5.6.3 Isolation Between Transmission And Reception. ............................................................. 35 Figure 5.6.4 Axial Ratio In Azimuth (a) And Elevation (b). ................................................................ 35 Figure 5.6.5 New Design With Isolators............................................................................................... 36 Figure 5.6.6 Radiation Pattern In Azimuth (Left) And Elevation (Right) In Polar. ............................. 36 Figure 5.6.7 Structure Of The New Design With Two Transmitters And Two Receivers. .................. 37 Figure 5.6.8 Scatting Parameters. ......................................................................................................... 37 Figure 5.6.9 Parameter S11 Of Combination Of Two Elements. ......................................................... 38 Figure 5.6.10 Radiation Pattern In Azimuth (a) And Elevation(b) In Polar. ........................................ 38 Figure 5.6.11 Radiation Pattern In Azimuth (a) And Elevation(b) In Cartesian. ................................. 38 Figure 5.7.1 Structure Of The Cylinder Array. .................................................................................... 39 Figure 5.7.2 Parameter S11. .................................................................................................................. 39 Figure 5.7.3 Radiation Pattern In Azimuth (Left) And Elevation(Right) In Polar. .............................. 40 Figure 5.7.4 Radiation Pattern In Azimuth (Left) And Elevation(Right) In Cartesian. ........................ 40 Figure 5.7.5 Random Combination of Two Elements. ......................................................................... 40 Figure 5.7.6 3D Directivity Pattern of the radiating elements at 5.065 GHz. ....................................... 41 Figure 5.7.7 Radiation Pattern In Azimuth(a) and Elevation(b). .......................................................... 41 Figure 5.7.8 Array Geometry. ............................................................................................................... 41 Figure 5.7.9 3D Directivity Pattern of the 8 radiating elements array activating 2 of them without phase shifters at 5.065 GHz. ................................................................................................................. 42 Figure 5.7.10 Radiation Pattern of the 8 radiating elements array activating 2 of them without phase shifters at 5.065 GHz. ........................................................................................................................... 42 Figure 5.7.11 Radiation Pattern of the 8 radiating elements array activating 2 of them without phase shifters at 5.065 GHz. ........................................................................................................................... 42 Figure 6.1.1 Illustration Of The Circular Patch and Microstrip Line. .................................................. 43 Figure 6.1.2 Illustration Of The Structure Of Ground Plane. ............................................................... 43 Figure 6.1.3 Illustration Of The Single Polarization Real Patch Antenna. ........................................... 44 Figure 6.2.1 Illustration Of The Measure Process. ............................................................................... 44 Figure 6.2.2 S-Parameters Measurements For The Single Polarization Of Prototype I. ...................... 45 Figure 6.2.3 S-Parameters Measurements For The Single Polarization Of Prototype II. ..................... 45 Figure 6.2.4 Measurement Setup Of One Prototype In The Anechoic Chamber At Polytechnic University of Madrid............................................................................................................................. 46 Figure 6.2.5 Measured co-pol. And cross-pol radiation Pattern Of A Single Patch At 5.03GHz. ........ 46 Figure 6.2.6 Measured co-pol. And cross-pol Pattern Of A Single Patch At 5.065 GHz. .................... 47 Figure 6.2.7 Measured co-pol. And cross-pol Pattern Of A Single Patch At 5.091GHz. ..................... 47 Figure 6.2.8 Measured Gain Of one Element of the prototype. ............................................................ 48.


(16) 1. 1. INTRODUCTION AND OBJECTIVES 1.1. INTRODUCTION Nowadays, the autonomy of UAV (unmannered aerial vehicle) is greatly restricted due to the communication links which connects the ground station to the UAV. The commonly used frequency bands include S, C and K band, which play the role of transmitting and receiving radio waves for the communication links within a visual range, however, this strategy is largely dependent on an ideal topography, which must have obstacles and tall buildings as few as possible to get a good communication link. In order to get a remote flying range for UAV, satellite is often employed as the communication relay, and despite of its independence of terrain, high cost has to be put in. So a communication link based on a circular array antenna is proposed to solve this dilemma, which can achieve a flying distance of 70 km with a second UAV as the communication relay. The whole communication system is presented in Fig. 1.1.1.. Figure 1.1.1 Long-Range UAV-Relay System.. The key point of the aerial link is the radiating system. In this design, the microstrip patch is selected as the basic radiating element owing to its low profile, small size, simple geometry and easiness of manufacture. The pre-design counted with only one antenna built up sixteenpatches and working as a transmitter and receiver at the same time, but it could drive to problems with isolation between channels. Consequently, there are two antennas, one for reception and another for transmission. Each one consists in a circular array with eight patches and only two or three patches are working together. A microcontroller decides which ones work depending on second UAV position. To avoid problems with vibration in aerial conditions, T/R circuit boards and patch antenna boards are assembled together..

(17) 2. 1.2. OBJECTIVES The outline of this final project is organized as follows: . Chapter 1 provides a brief introduction of this project and its motivation.. . Chapter 2 consists of a brief technical description focusing on the basis characteristics and typical feeding methods associated with the design of microstrip antennas.. . Chapter 3 explains the system specification (gain, beamwdith, polarization) and the process of designing one microstrip patch.. . Chapters 4 determine the number of arrays in a cylinder array antenna and the polarization type of one radiating element.. . Chapter 5 illustrates the simulation results (scattering parameters and radiation pattern) of different configuration of antennas for transmitting and receiving and the isolation between channel transmitter and receiving channel to avoid damaging the receiving channel when transmitting.. . Chapter 6 discusses the difference between the simulation and measurement results and summaries the conclusion of the final project and discuss the next step to achieve in the future..

(18) 3. 2. THEORY OF MICROSTRIP ANTENNAS 2.1. INTRODUCTION The invention of microstrip antennas has been attributed to several authors, although Deschamps was in 1953 the first to introduce such antennas at the 3rd USAF Symposium on Antennas [1]. However, it was not until the mid-1970’s with the development of printed-circuit technology that serious advancements in this type of antenna began. The development of microstrip antennas arose from the idea of utilizing printed-circuit technology not only for the circuit components and transmission lines, but also for the radiating elements of an electronic system. It was also at that time when the research publications started to flow with the appearance of the first design equations and when the first book on microstrip antennas was printed. Microstrip antenna technology has been the most rapidly developing topic in the antenna field in the last twenty-five years, receiving the creative attentions of academic, industrial and government engineers and researchers throughout the world. During this period there have been innumerable published journal articles, books, symposia sessions and short courses devoted to the subject of microstrip antennas and arrays. As an example, Bahl and Barthia [7] or James and Hall [9] wrote classical guide books that are still in use. An exhaustive handbook of microstrip antennas has been published by them. A wealth of information is now available about the microstrip patch antennas as a radiating element. As a result, those antennas have quickly evolved from academic novelty to commercial reality, with applications in a wide variety of microwave systems. In fact, microstrip patch antenna has been used in personal communications systems, mobile satellite communications, direct broadcast satellite, wireless local area networks and intelligent vehicle highway systems, such as military aircraft, missiles and rockets, because of its low profile, simple geometry, small size and low cost. And in the proposed antenna design, it is selected as the basic radiating element due to its so many advantages.. 2.2. BASIC CHARACTERISTICS 2.2.1.. BASIC PROPERTIES. Conventional microstrip antennas consist of a pair of parallel conducting layers separated from a dielectric layer, which is referred to as the substrate. As shown in Fig.2.2.1.. Figure 2.2.1 Typical Geometry Of a Microstrip Antenna.. In this configuration, the upper conducting layer or patch is the source of radiation where electromagnetic energy fringes off the edges of the patch and into the substrate. The lower conducting layer acts as a perfectly reflecting ground plane, bouncing energy back through the substrate and into the free space. Although similar in operation to a microstrip transmission line, the patch antenna is.

(19) 4 much large in volume. Physically, the patch is a thin conductor (normally copper) that is an appreciable fraction of wavelength in extent (0.25𝜆0 -1𝜆0 ), parallel to a ground plane and a small fraction of wavelength above the ground plane (0.003𝜆0 −0.2𝜆0 ). the patches are usually etched on the dielectric substrate. The substrate is usually non-magnetic. The relative permittivity of the substrate 𝑖𝑠 𝜖𝑟 , which enhances the fringing fields that account for radiation, but higher values may be used I special circumstances. In most practical applications, the shape of the patch are rectangular, square or circular, but the rectangular and square are probably the most commonly used microstrip patch antenna because of ease of analysis and fabrication, and their attractive radiation characteristics, especially low crosspolarization radiation. However, in general, any geometry is possible, as is shown in Fig. 2.2.2.. Figure 2.2.2 Typical Shapes Of Patch.. Microstrip patch antennas make efficient radiators and are widely used in antenna applications. With a simple geometry, patch antennas offer many advantages not commonly exhibited in other antenna configurations, such as helix, horn, and reflector. For example, they are extremely low profiles, lightweight, simple and inexpensive to fabricate using printed circuit board technology, compatible with microwave, and have the ability to conform to planar and non-planar surfaces. In addition, once the shape and operating mode of the patch are selected, designs become very versatile in terms of operating frequency, polarization, pattern, and impedance. The variety in designs that is possible with microstrip antennas probably exceeds that of any other type of antenna element. Despite the many advantages of patch antennas, they do have some considerable drawbacks. One of the main limitations with patch antennas is their inherently narrowband performance due to its resonant nature. With bandwidth as low as a few percent, broadband applications using conventional patch designs are limited. Some approaches have been developed for bandwidth enhancement: one way to increase the bandwidth is to either increase the height of the dielectric or decrease the dielectric constant. Other drawbacks of patch antennas include low efficiencies, limited power capacity (because of the small separation of the radiating patch and its ground plane), spurious feed radiation (due to the unwanted surface waves), poor polarization purity, and manufacturing tolerance problems. Though decades of research, it was identified that the performance and operation of a microstrip antenna is driven mainly by the geometry of the printed patch and the material characteristics of the substrate onto which the antenna is printed. Therefore, it is conceivable that with proper manipulations to the substrate, improved antenna performance can result. Commercial substrate materials are readily available for use at RF and microwave frequencies, specifically for the design of microstrip antennas and printed circuits. Selection is based on desired material characteristics for optimal performance over specific frequency ranges. Common manufacture specifications include dielectric constant, dissipation factor (loss tangent), thickness and Young’s modulus. Values for dielectric constants range from 1 ≤ 𝜀𝑟 ≤12 for operation at frequencies ranging from 1 to 100 GHz. The thickness of the substrate is of considerable importance when designing microstrip antennas. The most desirable substrates for antenna performance are the ones that are thick with a low dielectric.

(20) 5 constant. This intends to result in an antenna with a large bandwidth and high efficiency due to the loosely bound fringing fields. However, this comes at the expense of large volume antenna and increased probability of spurious feed radiation and surface wave formation. On the other hand, thin substrates with high dielectric constants reduce the overall size of the antenna, since the fringing fields are tightly bound to the substrate. With thin substrates, coupling and electromagnetic interference (EMI) issues are less probable. However, because of the relatively higher loss tangents (dissipation factors), they are less efficient and have relatively smaller bandwidths. Therefore, there is a fundamental trade off that must be evaluated in the initial stages of the microstrip antenna design, to obtain loosely bound fields to radiate into free space while keeping the fields tightly bound for the feeding circuitry an avoid EMI.. 2.2.2.. SURFACE WAVES. For over two decades, research scientists have developed several methods to increase the bandwidth of a patch antenna. Many of these techniques involve adjusting the placement or type of element used to feed the antenna. The simplest and most direct approach is to increase the thickness of the substrate, while using a low dielectric substrate. This can extend efficiency as much as 90% if the surface waves are not including and bandwidth up to 35%. However, surface waves must be included, since surface waves extract power from the direct radiation pattern resulting in increased side lobe levels, antenna loss, and a decrease in efficiency. Moreover, as explained in the section before, the probability of surface wave formation increases as the thickness of the substrate increases. Fig 2.2.3 shows the different types of waves in a microstrip antenna.. Figure 2.2.3 Different Types Of Waves In a Microstrip Patch Antenna.. As a patch antenna radiates, a portion of the total available power for direct radiation becomes trapped along the surface of the substrate. This trapped electromagnetic energy leads to the development of surface waves. In fact, the ratio of power that radiates into the substrate compared to the power that 3 radiates into air is approximately ( 𝜀𝑟 ⁄2 : 1). This is governed by the rules of the total internal reflection. The prevention of surface waves improves operational width, directivity, all while reducing sidelobes and coupling, which are common concerns in microstrip antenna designs. It will result in improvements in the radiation characteristics of the patch antenna by improving overall efficiency. Surface waves can be eliminated by using cavities, stacked substrate techniques or bandgap substrates. However, this has the fundamental drawback of increasing the weight, thickness, and complexity of the microstrip antenna, thus negating many of the advantages of using microstrip antennas. These complications and others prevent microstrip antennas from becoming the standard in the microwave telecommunications community.. 2.2.3.. FRINGING FIELDS. The radiating element of the microstrip antenna is a resonating structure. The patch resonates in one dimension (in its length) and radiates in the other (in its width). Thus, an electric field and corresponding ground plane currents are formed at the patch edges and that causes the radiation. The.

(21) 6 electric field exists between the patch and the ground plane. The E-field at one edge goes from ground to patch and on the other from the patch to the ground.. Figure 2.2.4 Electric Field In a Microstrip Antenna.. Because the dimensions of the patch are finite along the length and width, the fields at the edges of the patch undergo fringing. This results in fringing fields that account for radiation. The fringing fields show in Fig. 2.2.4, which can be represented by an equivalent magnetic surface 𝑀𝑠 current. Both are in the same direction, equal magnitude, and are separated by a distance of L. the amount of fringing is a function of the dimensions of the patch and the height of the substance. The fringing effect is associated with the thick low dielectric constant substrates. For the principal E-plane fringing is a function of the ratio of the length of the patch L to the height h of the substrate (L/h) and the dielectric constant 𝜀𝑟 of the substrate. Since for microstrip antennas L/h≫1, fringing is reduced. In practice, the fringing effect must be taken into account because it influences the resonant frequency of the antenna, so it acts as an additional length of the patch, as it is seen in Fig 2.2.5. It causes the effective distance between the radiating edges of the patch to be slightly greater than L. Because of the fringing effects, electrically the patch of the microstrip antenna looks greater than its physical dimensions. Therefore, in the section of antenna design, the calculation of patch has to take into account the fringing effects.. Figure 2.2.5 A Microstrip Patch Antenna Showing Fringing Fields.. 2.3. FEEDING METHODS There are several techniques to feed or transmit electromagnetic energy to a microstrip antenna. The most popular methods are:    . The microstrip transmission line The coaxial probe The aperture coupling The proximity coupling.

(22) 7 Typical feeding methods used to excite a microstrip patch antenna are illustrated as follow, corresponding equivalent circuits too:. Figure 2.3.1 Microstrip Line Configuration Using a Direct Approach.. Figure 2.3.2 : Probe Fed Configuration Using a Direct Contact Approach.. In each of equivalent circuits, an RLC circuit symbolizes the patch, illustrating its resonant nature. The resistance (R) corresponds to loss associated with the conductors (ground plane and patch) and substrate (loss tangent tang (𝛿)). The simplest methods of feeding the patch to realize are those of the coaxial probe and microstrip transmission line (protoetched on the substrate), illustrated in Fig. 2.3.1 and Fig. 2.3.2. The microstrip line feed is easy to fabricate, simple to match by controlling the inset position and rather simple model. Coaxial probe feed is also easy to fabricate and match. Both approaches utilize direct contact with the patch to induce excitation. The point of excitation (contact point) is adjustable, enabling the designer to control the impendence match between feed and antenna, polarization, mode of operation and excitation frequency. Generally, for direct contact feeds, the best impendence match is obtained when the contact point is off-centered. This produces asymmetries in the patch excitation, which generate higher order modes. These higher order modes induce a cross-polarized component in the principal plane antenna pattern, which draw power from the dominant 𝑇𝑀010 mode and results in degradation of the antenna’s main beam. Therefore, a trial-and-error approach is often used to obtain the optimum match for the direct contact feeds. Another disadvantage of the direct contact feeds is that they are inherently narrowband devices. These feeds, whether coaxial or microstrip, are matched to specific impendences (in most cases 50Ω) for a select range of frequencies. Operation outside this range automatically degrades antenna performance due to the inherent between the antenna and the feed..

(23) 8. Figure 2.3.3 Aperture-coupled (left) And Proximity-coupled (right) Configuration Using a Non-contacting approach.. To overcome some of the shortcomings of the direct-coupled feeds, a variety of “non-contacting coupled feeds” has been developed. The two main configurations are the aperture-coupled and proximity-coupled feeds (Fig 2.3.3). The aperture-coupled configuration consists of two parallel substrates separated by a ground plane. Excitation of the plane is accomplished by coupling energy from a microstrip line through a small aperture (slot) in the ground plane. With this arrangement, the microstrip feed is designed on a thin-high dielectric constant substrate, which tightly binds the field lines, while the patch is designed on a thick-low dielectric constant substrate. The ground plane isolates the feed from the patch, and thus minimizes spurious radiation from the feed, which would interfere with the antenna pattern. Therefore, the design of the patch and the transmission line are independent. In contrast, the proximity-coupled technology operates in a manner similar to that of the aperture-coupled configuration except the ground plane is removed. Both non-contacting feeds have similar advantages with the exception that the thickness changes with removal of the ground plane. In both non-contacting configurations, there is an undesirable increase in the removal of overall thickness of the antenna. These electromagnetic coupled (EMC) feed antennas have many advantages over microstrip transmission line and coaxial feed antennas like no physical contact between feed line and radiating element, no drilling required, less spurious radiation, better for array configuration, good suppression of higher order modes, good polarization purity, no cross-polarized radiation and better high frequency performance. Therefore, to reduce the complexity and size of the antennas involved in this research, the aperturecoupled and proximity-coupled feeds were eliminated. The microstrip transmission line feed was eliminated because of increasing the coupling between the patch and the feed and resulting in the generation of high cross-polarization levels. So, it was decided to design the structures using a coaxial probe feed. Indeed, there are significant drawbacks to using the coaxial probe approach, but substantial benefits: it has the wanted radiation, and simplicity in design and in construction is obtained when using them to feed a patch antenna designed with two substrate layers. Coaxial feeds are also widely used. The inner conductor of the coaxial-line is connected to the radiating patch, while the outer conductor is connected to the ground plane as shown in Fig 2.3.4.. Figure 2.3.4 A Patch Excited Using a Coaxial Probe..

(24) 9. 3. DESIGN OF A CIRCULAR MICROSTRIP PATCH ANTENNA This chapter details the design of the microstrip patch antenna and their simulated results obtained from the CST Studio Suite software. In order to define the design of the microstrip patch antenna, some common characteristics should be identified. The four parameters held constant throughout the study are the radius of the patch, the frequency of operation (5.065GHz), type of polarization and the dimensions and material properties of the dielectric substrates. The following procedures explain the analysis techniques required to design the patch antenna.. 3.1. SYSTEM SPECIFICATIONS First at all, we have to study various parameters for this application. The below table shows several parameters:. System Specifications Frequency Band Centre Frequency Polarization Elevation Azimuth Scope Gain of one radiating element Number of radiating element Configuration of Antenna Number of radiating element simultaneously activated. 5,03GHz – 5,091GHz 5,065GHz Linear o Circular ±25º 360º 70 km >8dBi 8 o 16 Tx and Rx with the same Antenna o Separately 2 , 3 or 4. Table 3.1.1 Antenna Performances.. 3.2. FRECUENCY PARAMETERS. SELECTION. AND. SUBSTRATE. The first step in designing the patch antenna wad to select the frequency of operation. Radiation Group of Signals, Systems and Radiocommunications Department decided to design the patch to work at C-Band, the centre frequency is 5,065GHz and the frequency band is from 5,03GHz to 5,091GHz. A continuation, we have to choose suitable dielectric substrate of appropriate thickness. The structure of the patch antenna employs a two-layers substrate as shown in Fig. 3.2, one for etching the patch and one for enhancing the bandwidth:.

(25) 10. Figure 3.2.1 Structure Of The Designed Patch Antenna.. The substrate parameters can be chosen independently. In this design we have two substrates, the lower substrate on which the patch is printed requires a relatively thin substrate with a low relative dielectric constant and the lower substrate requires a thick substrate with a low relative dielectric constant to increase bandwidth. For this reason, foam material is used, which provides sufficient mechanical stability as well as a dielectric constant close to air.. Characteristics Of Substrate Dielectric constant Dielectric loss @10 GHz Thickness (mm). FR 4 4.3 0.025 0.254(hFR4). FOAM 1.07 0.001 3 (hFOAM). Table 3.2.1 Characteristics Of Substrate.. The thickness of foam has to be 3 mm that´s the minimum value for enhancing enough the bandwidth (61 MHz) of the system specification. To evaluate the dimension of the patch antenna on this two-layers substrate with different dielectric constants ɛr FOAM and ɛr FR4 , an equivalent relative permittivity ɛre has to be calculated to substitute the two substrate for an equivalent layer substrate. For these two-layers , the equivalent relative permittivity ɛre can be evaluated using the equation[5] :. εre =. 𝜀𝑟𝐹𝑂𝐴𝑀 ∗𝜀𝑟𝐹𝑅4 ∗(ℎ𝐹𝑂𝐴𝑀 +ℎ𝐹𝑅4 ) 𝜀𝑟𝐹𝑂𝐴𝑀 ∗ℎ𝐹𝑅4 +𝜀𝑟𝐹𝑅4 ∗ℎ𝐹𝑂𝐴𝑀. (3.2). Where hFOAM is the foam thickness, hFR4 is the FR4 thickness , ɛr FOAM and ɛr FR4 are the foam and FR4 relative permittivity , respectively. Based on this expression, it can be shown mathematically that as hFOAM increases, ɛre decreases . We obtain for the equivalent relative permittivity:. ɛre=1,16 3.3. DESIGN OF PATCH Previously the antenna was configured as a circular patch. This simplifies the design since the dimensions are on the order of a half-wavelength. With the values for the dielectric constant of the substrates, resonant frequency (5.065GHz) and substrate thickness already specified, we can do these calculations easily..

(26) 11. 3.3.1.. DESIGN PROCEDURE. The usual design procedure is based on an estimation of resonating frequency for the individual patch carried out by using the cavity model. The radio R of the patch is slightly less than a half wavelength 𝜆. in the substrate ( 𝑔).We estimate a value for the effective relative permittivity ɛeff for this microstrip 2 lines for this circular antenna . We haven´t the expression to calculate the ɛeff for the circular antenna , so we approximate the value ɛeff as a square patch antenna . 𝜀𝑒𝑓𝑓 =. 𝜀𝑟𝑒 𝜀𝑟𝑒 − 1 + ∗ 2 2. 1 √1 + 12 𝑑 𝑤. For the total substrates thickness t= hFOAM +hFR4 =0,3254 cm. With this value of ɛeff , we may now calculate the radius of the antenna given by equation :. 𝐹=. 𝑟=. 8,791∗109. (3.3.1.2). 𝑓∗√𝜀𝑒𝑓𝑓. 𝐹 1 2 2𝑡 𝜋𝐹 {1+ [ln( )+1,7726]} 𝜋𝐹𝜀𝑒𝑓𝑓 2𝑡. (cm). (3.3.1.3). With f = 5,065*109 Hz, ɛeff =1,15 and t=0,3245 cm , we obtained the value of the radio of the circular patch : 13,5 mm . Before concluding the usual design procedure, the location of the feed point must be determined. In our case, the single circular antenna element is fed by a direct connection to a 50 Ω coaxial feeder. For a feed point at the radiating edge, the input impedance is maximum, so we can have maximum transference of power, and for a feed point at the centre of patch, input impedance is zero and increases along the axis [6]. So, the input impedance can be controlled by adjusting the position of the feed point. The input impedance matched to a 50 Ω may be achieved by suitably locating the feed point. As was the case for the rectangular patch antenna, the input impedance of a circular patch at resonance is real. The input power is independent of the feed point position along the circumference. Take the reference of the feed at φ=0º, the input resistance at any radial distance ρ´= ρ0 from the center of the patch can be written as: 2 (𝑘𝜌 ) 1 𝐽𝑚 0 (𝛺) 2 𝑡 𝐽𝑚 (𝑘𝑎𝑒 ). 𝑅𝑖𝑛 (ρ´ = ρ0 ) = 𝐺. (3.3.1.4). Where Gt is the total conductance, ae is the effective radius. 𝑎𝑒 = 𝑎 ∗. 1 −1 2 2𝑡 𝜋𝑎 {1+ [ln( )+1,7726]} 𝜋𝑎𝜀𝑒𝑓𝑓 2𝑡. (3.3.1.5). Where Gt is the total conductance due to radiation, conduction and dielectric losses. As was the case with the rectangular patch , the resonant input resistance of a circular patch with an inset feed, which is usually a probe , can be written as: 𝑅𝑖𝑛 (ρ´ = ρ0 ) = 𝑅𝑖𝑛(ρ´ = ae ) =. 2 (𝑘𝜌 ) 1 𝐽𝑚 0 2 (𝑘𝑎 ) (𝛺) 𝐺𝑡 𝐽𝑚 𝑒. (3.3.1.6).

(27) 12. This is analogous to for the rectangular patch. So using previous formulas, we find the location of the feed point is approximately 5,5mm from the center of the circular patch. Now we have all dimensions of the patch and the impedance location, the final step in the design was to verify patch resonance and the location of the feed. We will utilize Microwave Studio to accomplish this step.. 3.3.2.. SELECTION OF POLARIZATION. In order to select the polarization of the patch, we have two possible configurations, polarization linear o polarization circular. The configuration of polarization linear is also simple. We also have a feed point in a coordinate axis. For example, if the feed point is on the coordinate Y, it will be polarization lineal vertical as shown in Fig 3.3.1(left). A microstrip patch antenna is able to radiate dual linearly polarize waves by excitation through two suitable orthogonal different feed points. The antenna has two individual feeds corresponding to two orthogonal linear polarizations as shown in Fig 3.3.1(right).. (a)Linear Polarization.. (b) Circular Polarization.. Figure 3.3.1 Example Of Lineal Polarization And Example Of Dual Polarization By Excitation Through Two Suitable Orthogonal Different Feed Points.. Dual polarization is commonly used in microstrip patch and array antennas like in aerial communication systems. For example, it allows to increase the communication capacity in a band to re-utilize it in polarization. Microstrip patch antenna with circular geometries are suitable shape to produce dual linearly waves. But , it does have a drawback : circular patches may results in the generation of high cross polarization levels when dual or circular polarization is required [7].In dual polarization , the two linear polarization are orthogonal to each other like in circular polarization . But , the two feed point are excited though two terminals that are completely independent to each other with equal amplitude conditions on the contrary , of the circular polarization that is excited through two orthogonal terminals 90º out of phase and with the equal amplitude conditions . The patch with circular polarization is better than patch with lineal polarization because it have less loss in radio communications..

(28) 13. 3.3.3.. DESIGN OF MICROSTRIP TRANSMISSION LINE. We use microstrip transmission line to feed energy to a patch antenna . For this design, we introduce another substrate on the another face of the ground plane and it share grand plane with the patch antenna. So the modified structure is illustrated as follow (Fig.3.3.2).. Figure 3.3.2 Structure With Microstrip Line.. Figure 3.3.3 Equivalent Circuit.. Fig.3.3.3 presents a 3 dB microstrip T-junction power divider. This power divider consists in dividing the input power in two ways equally. This type of dividers has three different sections:   . Input port Quarter-wave transformer Output ports. The input impedance is 50 Ω (Z0), and we have two Output ports orthogonal with 50 Ω each other. In order to transform 50//50 Ω to 50 Ω, we use the quarter-wave transformer to adapt the input impedance to the equivalent output impedance. Fig.3.3.4 shows the quarter-wave transformer parts are called as quarter-wave transformer because of. the length of these parts. The length of these parts are equal to the one fourth of the wavelength of the electromagnetic wave (𝜆𝑔 /4), which is propagating in this three port network. The impedance of the quarter-wave transformer is √𝑍𝑖 𝑍𝑙 where Zi is the input impedance and Zl is the equivalent output impedance..

(29) 14. Figure 3.3.4 3dB Microstrip T-Junction Power Divider.. Fig.3.3.5 and Fig.3.3.6 present the circular patch antenna with circular polarization using the 3dB Microstrip T-Junction Power Divider which is presents in Fig.3.3.3.. Figure 3.3.5 Feeds Points (Side).. Figure 3.3.6 Feeds Points (TOP).. The first step in designing the feeding network was to choose a suitable dielectric substrate. We used a high frequency copper-clad substrates for Radio Frequency and microwave circuits, and we can used the same dielectric substrate to suit posterior active elements: Taconic TLY-5A: Dielectric constant: ɛr=2.17; Dielectric loss @10 GHz : tan() = 0.0009 Thickness h : 0.5 mm The Taconic TLY-5A copper clad has been specifically designed for high frequency circuits. Its dielectric constant is low and stable when used over broad temperature and humidity operating ranges. The specifications for the feed network are:  . Impedance Zo of all ports = 50 Ω Centre Frequency = 5.065GHz.

(30) 15 For the design, we have to determine the widths W of different parts of the power divider. We use the macro option en CST Microwave Studio Suite to determine the width of the lines, when knowing the characteristic impedance of the lines:. Figure 3.3.7 Macro Option CST Microwave Studio Suite.. Fig. 3.3.8 shows the structure of a microstrip line; where W is the width of the microstrip line, Zo is its characteristic impedance, t is its thickness and h is the dielectric substrate thickness.. Figure 3.3.8 Structure Of a Microstrip Line.. In the input port we have a microstrip line with the characteristic impedance 50 Ω.. CST Macro Option. Width(W). Characteristic Impedance (Ω). 1.56. 50,15. 1.567. 50.00. Table 3.3.1 Tabulated Comparison for the Determination Of Microstrip Power Divider Lines Width Of Zo= 50 Ω.. For the output ports, the line impedance is 50 Ω for each port and the equivalent impedance of two parallel ports 50//50 Ω is 25 Ω , but the width is the same as the input port . The length of the power divider lines is arbitrary. It does not have an influence on the valor of the microstrip line characteristic impedance. The length depends of the feeding network disposition..

(31) 16 For the 𝜆𝑔 /4 transformer : 𝑍𝜆𝑔 =√𝑍𝑖 𝑍𝑙 wich Zi is the input impedance = 50Ω and Zl is the equivalent impedance of two output ports in parallel 50//50 Ω = 25 Ω , so the line impedance of 𝜆𝑔 /4 transformer is 35 Ω (Fig 3.3.4).. CST Macro Option. Width(W). Characteristic Impedance (Ω). 2.576. 35. 2.55. 35.22. Table 3.3.2 Tabulated Comparison For The Determination Of Microstrip Power Divider Lines Width Of Z_λg= 35 Ω.. Those tables are just a comparison between the calculations and the CST Macro Option results. We notice that the results are in concordance. The difference of the calculation come from the decimals numbers considered in the calculations. The 𝜆𝑔 /4 transformer length : 𝜆𝑜 √𝜀𝑒𝑓𝑓. 𝜆𝑔 = = 10.74 𝑚𝑚 4 4 Where 𝜆𝑔 is the guide-wavelength in the microstrip line. It is smaller than the wavelength in the freespace 𝜆𝑜 . 𝜀𝑒𝑓𝑓 = 1.90 is the effective relative dielectric permittivity determined from CST Macro Option and the equation (3.3.7). If for disposition reasons, we have to do corners in the microstrip line , it is important to cut those corners as shown in Fig 3.3.9 because the sharp corners bring breaking impedances :. Figure 3.3.9 The Corners In Microstrip Line Have To Be Cut To Preserve a Constant Impedance..

(32) 17. 4. DESIGN OF CYLINDER ARRAY ANTENNAS 4.1. ARRAY ANTENNA CHARACTERISTICS An antenna array is an arrangement of 𝑁 number of individual and similar antennas each separated by a distance. Array antennas have superior characteristics when compared to an individual element especially with improved directivity. A group of similar antennas is an array if and only if the number of elements is more than one. A minimum number of elements that exist in an array are two. As 𝑁 increases the performance of the array antenna increases. Therefore, in practice, arrays have more elements sometimes with N value of several thousands of elements. The main characteristics of an array antenna are explained by the Array Factor and its Array Pattern. Interpretation of these two gives the efficiency of an array antenna for the specified values of design which involves the side lobe levels, beam steering capability as major performance indicators.. 4.1.1.. ARRAY FACTOR. The Array Factor is calculated as a function of the arrangement of elements in the array and excitation to each and every element. By adapting these parameters the array antenna performance may be optimized to achieve desirable array patterns. The Array Factor 𝐴𝐹 of a linear array antenna is given by Equation (4.1) 𝑁 (𝜃) = ∑ (𝑛−1) (𝑘𝑑 𝑐𝑜𝑠 𝜃+𝜑) 𝑛=1. (4.1). Where:     . 𝜃 is the angle between the axis of the array and the vector drawn from the origin to the point of observation 𝐴𝐹(𝜃) is the Array Factor plotted w.r.t variations in θ 𝑘 = 2𝜋⁄𝜆 𝑑 is the distance between the two elements in the array 𝜑 is the phase shift 𝑁 is the Number of elements in the array antenna. The above expression holds good only for identical elements which are equidistant. From the above expression it is evident that the Array Factor depends upon the number of elements, the distance or spacing between the elements, their excitation magnitudes and phases between elements. Once the array antenna is deployed into the field, i.e., after manufacturing the array of 𝑁 number of elements and with a fixed spacing between them, the only cause of deviations in the array factor and thereby the error in the array pattern will be due to the excitations that will be fed to the array. Hence the work on resynthesis of array pattern is made possible by correcting these excitation magnitudes and phases.. 4.1.2.. ARRAY PATTERN. The array pattern is the resultant of the simple multiplication of the array factor with the radiation pattern of the individual element. 𝐴𝑟𝑟𝑎𝑦 𝑃𝑎𝑡𝑡𝑒𝑟𝑛 = 𝐴𝑟𝑟𝑎𝑦 𝑓𝑎𝑐𝑡𝑜𝑟 × 𝑅𝑎𝑑𝑖𝑎𝑡𝑖𝑜𝑛 𝑝𝑎𝑡𝑡𝑒𝑟𝑛 𝑜𝑓 𝑠𝑖𝑛𝑔𝑙𝑒 𝑒𝑙𝑒𝑚𝑒𝑛𝑡.

(33) 18 This is the phenomenon which is referred to as “Pattern Multiplication” in the literature [5]. One may note that the array pattern is usually called on where the array is built from similar antenna elements.. 4.1.3.. MAIN LOBE AND SIDELOBE LEVELS. Major lobe or Main lobe is a part of the radiation pattern or the array pattern which is expected to deliver the maximum of radiated power in the desired direction. Hence it is the important parameter of interest with respect to directive arrays. The radiated power which is directed towards undesired directions is also concentrated in the form of lobes other than the main lobe and these lobes are referred to as “Side lobes”. The level of side lobe is never expected to be more than the main lobe and if it happens to be dominating the major lobe, it is considered as a case of serious degradation in the performance of an array. So all the specifications come with a certain limitation on the side lobe level that can be tolerated in the design of an array antenna.. 4.1.4.. ELEMENT SPACING. The spacing between the elements in an array plays an important role in minimizing the beamwidths of the array and as well as in minimizing the side lobe levels. As the spacing between the elements increases, the side lobe levels increase and also broaden the beamwidths. This can be assumed as the main reason in degradation of array pattern, whenever, element failures exist in between the array elements [5]. Suppose if one element fails in between two elements in an array antenna with 3 elements which are spaced equidistant by half wavelength, then the practical distance between the 1st and the 3rd element is one wavelength, when 2nd element has failed. Hence, the array factor changes and results in deviations in the observed pattern from the expected one.. 4.1.5.. GRATING LOBES. Grating lobes which contain same or more amount of radiated power when compared to the main lobe are called Grating lobes. High deviations in transmission or reception of signals occur due to grating lobes. A typical example worked out in resulted in Grating lobes resembling the Main lobe and is shown in Fig 4.1.1.. Figure 4.1.1 A Typical Example Of Grating Lobes Resembling The Main Lobe..

(34) 19. Grating lobes can be avoided in the visible space if the spacing between elements is chosen such that 𝑑 ≤ 𝜆/(1+𝑠𝑖𝑛𝜃𝑠). (4.1.5). where 𝑑 is spacing between elements, 𝜆 is wavelength and 𝜃𝑠 is scan angle If 𝑑 ≈ 0.9𝜆 in Equation (4.1.5), maximum directivity is achieved for an array. However, for this spacing, the maximum scan angle in a given geometric plane is approximately 6º. Since the requirement is to scan ±25º, the spacing needs to be less than 0.59𝜆. At the higher frequency this gives a spacing of 𝑑 = 40 m𝑚. Hence, in both vertical and horizontal planes of the array, the spacing is chosen to be 40 mm. This chapter details the design of different configuration of cylinder array using 8, 16 or 32 radiating elements. These are some important parameters that we have to study:    . Radius of the cylinder Number of radiating elements Number of active radiating elements simultaneously Antenna for transmitter and receiver using the same antenna o separately. 4.2. RADIUS OF THE CYLINDER To avoid the problem of grating lobes, the space between radiating elements have to be less than 0.7 , this condition limits the patch´s ground plane size. So we study in these three conditions: 𝑐 𝜆= = 57.26 𝑚𝑚 𝑓 ∗ √𝜀𝑒   . Space between elements 0.50 = 28,64 mm Space between elements 0.60 =34,35 mm Space between elements 0.70=40.08 mm. Figure 4.2.1 shows the structure which we have to study to determine the radius of cylinder array .. Figure 4.2.1 Structure between Two Consecutive Elements..

(35) 20 Where: W is the size of the patch d is the space between elements R is the radius of the cylinder array  is the angle between radiating elements  is 90º-/2. 𝛼=. 360 𝑁. (4.2.1.1). Where N is the number of elements Using the cosine theorem. 𝑅 2 = 𝑅 2 + 𝑑2 − 2 ∗ 𝑅 ∗ 𝑑 ∗ cos 𝛽. (4.2.1.2). We can obtain the relation between the radius of the cylinder and the distance between elements. Using the follow expression, we can obtain the relation between the radius and the size of the patch: 𝛼. Cos 4 = 𝑅=. 𝑑⁄ 2. (4.2.1.3). 𝑊 2. 𝑊. (4.2.1.4). 𝛼 2. 2∗tan. 𝑑 = 𝑊 ∗ cos. 𝛼 4. (4.2.1.5). N=8. N=16. W=30 mm. W= 40 mm. W= 50 mm. W=30 mm. W= 40 mm. W= 50 mm. . 45º. 45º. 45º. 22.5º. 22.5º. 22.5º. d. 29.42 mm. 39.23 mm. 49.03 mm. 30 mm. 40 mm. 50 mm. R. 36.21 mm. 48.309 mm. 60.386 mm. 75.41 mm. 100.54 mm. 125.68 mm. Table 4.2.1 Comparison Of Different Configuration Of Cylinder Array.. In this table we can observe that the best option to avoid grating lobes is W= 30 mm with eight o sixteen elements.. 4.3. ARRAY CONFIGURATION In this step, we will study the configuration of the cylinder array with eight or sixteen radiating elements. First at all, we have to design the structure of the array and then estimate the gain with number of active elements simultaneously..

(36) 21. 4.3.1.. CYLINDER ARRAY WITH EIGHT ELEMENTS. Fig. 4.3.1 presents the structure of a cylinder array with eight radiating elements, which we mention in Table 4.2.1:. Figure 4.3.1 Cylinder Array With Eight Radiating Elements.. Fig.4.3.2 shows the posterior system architecture which we separate transmission and reception , which they are entirely independent.. Figure 4.3.2 System Architecture Using Eight Elements.. In this configuration, we can observe the radius is bigger than the theoretical radius because in theoretical calculations we considered the height of patch is despicable. If we active two elements simultaneously, we have eight combinations of two elements. The electromagnetic wave arrives to each radiating element at the same time. So we haven´t to introduce phase shifters, that means a saving in manufacturing time..

(37) 22 The gain with two active radiating elements simultaneously will increase 3dB respect to one active element.. 4.3.2.. CYLINDER ARRAY WITH SIXTEEN ELEMENTS. Fig. 4.3.2 presents the structure of a cylinder array using sixteen radiating elements, which we mention in Table 4.2.1:. Figure 4.3.3 Cylinder Array With 16 Radiating Elements.. Fig.4.3.4 shows the posterior system architecture which we use one antenna for transmission and reception. In this architecture we use a circulator to divide transmission and reception.. Figure 4.3.4 Diagram Of Transmission And Reception Using Sixteen Elements.. In this configuration, we can observe the radius is bigger than the theoretical radius with the same reasoning as above. If we active two elements simultaneously, the result is the same as the.

(38) 23 configuration with eight elements. So we discard this configuration and we will study the action with three o four elements active simultaneously. In the case of activation of three elements simultaneously, we have to use two shifters to compensate the delay arrival in the two radiating elements in the extremes. The gain with three elements will increase 4.7 dB respect one active element. In the case of activation of four elements simultaneously, we have to use two shifters to compensate the delay arrival too. The gain with four elements will increase 6 dB respect one active element. If we don´t introduce the shifters, the increase of gain will be less because the radiation pattern of one element doesn´t change the steering direction to contribute the global radiating pattern with four elements. Fig.4.3.5 shows the radiation pattern without shifters.. Figure 4.3.5 Structure With 16 Radiating Elements Without Shifters..

(39) 24. 5. ANTENNA SIMULATIONS 5.1. SIMULATION OF A LINEAR POLARIZATION PATCH ANTENNA Fig.5.1.1. presents the design of a circular patch antenna with linear polarization. The radius of the patch is 13.4 mm and the excitation point is 5.5 from center of the patch on the x-axis.. Figure 5.1.1 Circular Patch Design With Lineal Polarization.. Fig.5.1.2(a) presents the simulated S-parameter and the input impedance of the patch. The simulated return loss (S11) of the patch in our working band are below than -21dB. Fig.5.1.2(b) presents the Smith chart plots of S11 for the linear polarization patch antenna.. (a) Figure 5.1.2 Parameter S11 (a) and Smith Chart (b).. (b).

(40) 25. 5.2. SIMULATION OF CIRCULAR POLARIZATION 5.2.1. SIMULATION OF CIRCULAR POLARIZATION WITH IDEAL PORTS Fig.5.2.1(a) presents the patch antenna with circular polarization. The two excitation points are perpendicular and at 5,5mm from the centre, on the x-axis and y-axis respectively. Fig.5.2.1(b) presents the sweep of the radius of the circular patch keeping the positions of the excitation points.. (a). (b). Figure 5.2.1 Patch With Circular Polarization And Sweep Of The Radius.. Fig.5.2.2(a) presents the simulated S-parameter and the input impedance of the patch. The simulated return loss (S11) of the patch in our working band are below than -20dB. Fig.5.2.2(b) presents the Smith chart plots of S11 for the circular polarization patch antenna.. (a). Figure 5.2.2 Parameter S11 (a) and Smith Chart (b).. (b).

(41) 26 Fig.5.2.3 presents the radiation pattern in azimuth (Phi=0º) and elevation (Phi=90º) in Polar:. (a). (b). Figure 5.2.3 Radiation Pattern In Azimuth (a) And Elevation(b).. Fig.5.2.4 presents the radiation pattern in azimuth (Phi=0º) and elevation (Phi=90º) in Cartesian:. (a). (b). Figure 5.2.4 Radiation Pattern In Azimuth (a) And Elevation(b).. Fig.5.2.5 presents the axial ratio in azimuth (Phi=0º) and elevation (Phi=90º):. (a) Figure 5.2.5 Axial Ratio In Azimuth (a) And Elevation (b).. (b).

(42) 27 Fig.5.2.6 presents the relation polar-contrapolar of the circular patch antenna.. Figure 5.2.6 Relation Polar(Red)-Contrapolar (Green).. In the previous figures, present the result of the simulation of a circular patch with circular polarization. We can observe that the return loss (S11) is similar to the patch with linear polarization, the directivity is approximately 8.6 dB The parameter most important is axial ratio, they are below than 2 dB.. 5.2.2. SIMULATION OF 3DB MICROSTRIP T-JUNCTION POWER DIVIDER Fig.5.2.7, presents the circuit which can generate two orthogonal linear polarizations to obtain circular polarization.. Figure 5.2.7 Design Of 3dB Microstrip T-Junction Power Divider.. Fig.5.2.8 (a) presents the scatting parameters in magnitudes, we can observe the return loss (S11) in the input port is approximately -40 dB and the other two output ports are -3dB. Fig.5.2.8 (b) presents the scatting parameters in phase, the phase of input port is not important, but we can observe the phase difference between port 2 and port 3 is 90º..

(43) 28. (a). (b). Figure 5.2.8 Scatting Parameters In Magnitudes (a) And Phase (b).. 5.2.3. SIMULATION OF PATCH WITH 3DB MICROSTRIP TJUNCTION POWER DIVIDER Fig.5.2.9(a) present the view of the top of the patch antenna with circular polarization and Fig.5.2.9(b) present the view of the bottom of the patch antenna with circular polarization.. (Top). (Bottom). Figure 5.2.9 Patch Design With Microstrip Line Feeding.. Fig.5.2.10(a) presents the simulated return loss (S11) of the patch in our working band are below than -24dB and Fig.5.2.10(b) presents the Smith chart plots of S11 for the circular polarization patch antenna.. (a). (b) Figure 5.2.10 Parameter S11 (a) and Smith Chart (b)..

(44) 29 Fig.5.2.11 presents the axial ratio in azimuth (Phi=0º) and elevation (Phi=90º):. (a). (b) Figure 5.2.11 Axial Ratio In Azimuth (a) And Elevation (b).. Fig.5.2.12 present the radiation pattern 3D of the patch witch circular polarization:. Figure 5.2.12 Radiation Pattern en 3D.. In this point, we use the 3 dB T-junction Power Divider to feed the antenna instead of using ideal ports. We can observe that the result is similar, but the only difference is the axial ratio is worse.. 5.3. STUDY OF NUMBER OF RADIATING ELEMENTS Fig.5.3.1 present the design of a simple patch or two patches ,which we have to study to decide how many patches we should use :. (a). (b). Figure 5.3.1 Design of A Simple Patch (a) And Two Patches (b)..

(45) 30 Fig.5.3.2 presents the radiation pattern in azimuth (Phi=0º) and elevation (Phi=90º) in Polar using one patch:. (a). (b). Figure 5.3.2 Radiation Pattern In Azimuth (a) And Elevation (b) Of Simple Patch.. Fig.5.3.2 presents the radiation pattern in azimuth (Phi=0º) and elevation (Phi=90º) in Polar using two patches:. (a). (b). Figure 5.3.3 Radiation Pattern In Azimuth (Left) And Elevation (Right) Of Two Patches.. Fig.5.3.2 presents the radiation pattern using one patch, we can observe the gain is 8.5 dB; the side lobe level is approximately -14 dB in elevation Fig.5.3.3 presents the radiation pattern using two patch, we can observe the gain is 10.2 dB; the side lobe level is approximately -20 dB in elevation. Using this configuration, we can increase 1.7 dB, but the speciation of beamwidth in elevation limit the size of ground plane and we cannot manufacture it..

(46) 31 So we discard the configuration using two patch because the gain increase is not so much and we will have difficulty to manufacture it.. 5.4. STUDY ON THE INFLUENCE OF GROUND PLANE Fig.5.4.1 (a) presents the patch antenna with a ground plane 36x36 mm and Fig.5.4.2 presents the patch antenna with a ground plane 60x60 mm:. (a). (b). Figure 5.4.1 Patch Design With Different Ground Plane 36x36 mm (a) 60x60 mm (b).. Fig.5.4.2 and Fig.5.4.3 present the radiation pattern and directivity of the patch using a bigger ground plane, the obtained result shows that the increase of ground plane size improve the directivity and narrow the beamwidth.. Figure 5.4.2 Radiation Pattern In 3D with Ground Plane 60 x 60 mm.. (a). (b). Figure 5.4.3 Radiation Pattern In Azimuth (a) And Elevation (b)..

(47) 32. 5.5. CYLINDER ARRAY USING SIXTEEN ELEMENTS FOR TRANSMISSION AND RECEPTION Fig.5.5.1 present the structure of cylinder array with sixteen radiating elements with circular polarization:. Figure 5.5.1 Structure of Cylinder Array With Sixteen Elements.. 5.5.1. SIMULATION OF COMBINATION OF FOUR RADIATING ELEMENTS Fig.5.5.2(a) presents the simulated return loss (S11) of the circular patch in our working band are below than -25dB; we can observe that we have a double resonance in 5GHz and 5.2GHz. Fig.5.5.2(b) presents the Smith chart plots of S11 for the circular polarization patch antenna.. (a) Figure 5.5.2 Parameter S11 (a) and Smith Chart (b).. (b).

(48) 33 Fig.5.5.3 presents the radiation pattern en 3D of the combination of four radiating elements:. Figure 5.5.3 Radiation Pattern En 3D.. Fig.5.5.4 presents the radiation pattern in azimuth (Phi=0º) and elevation (Phi=90º) in Polar:. (a). (b). Figure 5.5.4 Radiation Pattern In Azimuth (a) And Elevation(b) In Polar.. Fig.5.5.4 presents the radiation pattern in azimuth (Phi=0º) and elevation (Phi=90º) in Cartesian:. (a). (b). Figure 5.5.5 Radiation Pattern In Azimuth (a) And Elevation(b) In Cartesian..