This thesis concentrates on the antenna design for only on-body power transmission; however, the antenna design to transmit energy to an implanted sensor at mid-field is still under development in the community [131]. A wearable low frequency coil array for a near-field energy transfer to band-aid sensor has been investigated, but optimized design for a such array at microwave frequency to power up a mid-field implanted cardiac sensor is still not developed [131]. Recently, it has been reported that the advantages using the 1.7 GHz over 200 MHz in terms of the compactness and power efficiency in simulation as shown in Figure 6.1.
Figure 6.1: Wireless power transmission using 1.7 GHz (right) and 200 MHz (left). Red indicates more power transmitted as shown in the right [131].
136
As the orientation of the antenna inside the body is unknown and changing, the powering antenna outside the body should be CP so that the power transmission efficiency is unchanged and independent to the orientations [132, 133]. Therefore, the CP textile antenna developed in this thesis may be a possible candidate for the above application.
Figure 6.2: Wirelessly-powered ingestible camera from the Chinese University of Hong Kong [132].
Although the single feed CP antennas in Chapter 3 and 4 are very simple to implement and have very wide impedance and axial ratio bandwidths; however the radiation with good axial ratio only covers limited solid angle close to the centre of the antenna. A CP wide-slot antenna with multiple feed lines has never been reported and it may significantly improve the solid angle coverage with good axial ratio if the similar feeding structure of the wideband CP patch antenna can be applied as shown in Figure 3.4 [74].
137
APPENDIX
//For RF2401A transmitter /*
config_setup word 16 bits
23: 0 Payloads have an 8 bit address 22: 0 21: 1 20: 0 19: 0 18: 0 17: 1 16-Bit CRC 16: 1 CRC Enabled
15: 0 One channel receive 14: 1 ShockBurst Mode 13: 1 1Mbps Transmission Rate 12: 0 11: 1 10: 1 9: 1 RF Output Power 8: 0 RF Output Power
7: 0 Channel select (channel 2) 6: 0
138 5: 0 4: 0 3: 0 2: 1 1: 0 0: 0 Transmit mode (0=Tx, 1=Rx) */ #include <htc.h>
#define _XTAL_FREQ 2000000 // oscillator frequency for _delay()
// Config: ext reset, no code protect, no brownout detect, no watchdog,
// power-up timer enabled, 4MHz int clock
__CONFIG(MCLRE_OFF & CP_OFF & BOREN_OFF & WDTE_OFF & PWRTE_OFF & FOSC_INTOSC);
#define TX_CE LATA1 //Enable transmission
#define TX_CS LATA0 //Enable configuration
#define TX_CLK1 LATA4 //Clocking for N2401
#define TX_DATA LATA5 //Data for N2401
#define SENSOR RA2 //Sensor input
unsigned char data_array[4]; //8-bit data
139 void configure_transmitter(void); void transmit_data(void);
void main() {
unsigned char dcnt; // delay counter unsigned char i;
// Initialisation
TRISA = 0b000100; //Config RA2 as input
ANSA2 = 1; //RA2 as analogue sensor input
IRCF3 = 1; // 1101 4 MHz IRCF2 = 1; // 1100 2 MHz IRCF1 = 0; // 1011 1 MHz IRCF0 = 0; // 0111 500kHz(default) // configure ADC ADCON1 = 0b01000011;
//0--- MSB of result in ADRESH<7> (ADFM = 0) //-100---- Tad = Fosc/4 = 1 MHz)
//---00 Use VCC
//---11 Use internal Vref
ADCON0 = 0b00001001; //-11101-- select temp sensor
//-11111-- FVR output //-00001-- AN1
140 //-00010-- AN2
//---1 turn ADC on (ADON = 1) FVRCON = 0b10000010;
//1--- enable fixed voltage reference //--1--- enable temperature sensor
//---0---- enable low range
//---10 ADC 2.048V fixed voltage ref //---01 ADC 1.024V fixed voltage ref //initialize the received data array data_array[2] = 0x00; data_array[3] = 0x00; // Main loop for (;;) { __delay_ms(1); __delay_us(500);
//3ms requirement from powerup to active for n2401 //But can be smaller than 3 ms
configure_transmitter(); //configure the transmitter
GO_nDONE = 1; // start conversion while (GO_nDONE) // wait until done ;
141
//10 bits result
data_array[0]= ADRESH; //Top 8-bit ADC result
data_array[1]= ADRESL; //Low 2-bit ADC result, MSB justified data_array[2]= ADRESH; //Top 8-bit ADC result
data_array[3]= ADRESL; //Low 2-bit ADC result, MSB justified
__delay_ms(1);
__delay_us(500); //Can be smaller than 300us ~250us
transmit_data(); //We send 4 bytes
} }
void configure_transmitter(void) {
unsigned char i;
unsigned long config_setup; //Config Mode
TX_CE = 0; TX_CS = 1;
//Delay of 5us from CS to Data is taken care of by the for loop //Setup configuration word, we only need upper 24 bits, zero pad the lower 8 bits
142 config_setup = 0b00100011011011111111001000000000; // ---1111001---RF freq // ---10---RF power 10 = -5db // ---1---enable 1Mbps // ---1---CRC enable // ---1---16 bit CRC for(i = 0 ; i < 24 ; i++) {
TX_DATA = (config_setup & 0x80000000) > 0; //Display data
TX_CLK1 = 1; TX_CLK1 = 0;
config_setup <<= 1 ; //shift 1 bit to left }
//Configuration is active on falling edge of CS TX_CE = 0;
TX_CS = 0; }
//This sends out the data stored in the data_array
//data_array must be setup before calling this function void transmit_data(void)
143 unsigned char i, j;
unsigned char temp, rf_address; //8-bit RF address TX_CE = 1;
//Clock in address
rf_address = 0b11100111; //Power-on Default for all units for(i = 0 ; i < 8 ; i++)
{
TX_DATA = (rf_address & 0x80) > 0; //Display data TX_CLK1 = 1;
TX_CLK1 = 0;
rf_address <<= 1 ; //shift 1 bit to left }
//Clock in the data_array
for(i = 0 ; i < 4 ; i++) //4 bytes {
temp = data_array[i];
for(j = 0 ; j < 8 ; j++) //One bit at a time {
TX_DATA = (temp & 0x80) > 0; //Display data
TX_CLK1 = 1; TX_CLK1 = 0;
144 }
}
TX_CE = 0; //Start transmission }
145
BIBLIOGRAPHY
[1] C. M. Ghiglino, "Ultra-Wideband (UWB) rectenna design for Electromagnetic Energy Harvesting," in Department of Signal Theory and Communications. Degree of Engineer Catalonia: Polytechnic University of Catalonia, 2010.
[2] G. A. Vera, "Effcient Rectenna Design for Ambient Microwave Energy Recycling," in
Department of Signal Theory and Communications. Degree of Engineer Catalonia:
Polytechnic University of Catalonia 2009, p. 115.
[3] W. C. Brown, "The History of Power Transmission by Radio Waves," Microwave Theory
and Techniques, IEEE Transactions on, vol. 32, pp. 1230-1242, 1984.
[4] H. Jabbar, Y. S. Song, and T. T. Jeong, "RF energy harvesting system and circuits for charging of mobile devices," Consumer Electronics, IEEE Transactions on, vol. 56, pp. 247-253, 2010.
[5] T. Paing, E. Falkenstein, R. Zane, and Z. Popovic, "Custom IC for Ultra-low Power RF Energy Harvesting," in Applied Power Electronics Conference and Exposition, 2009.
146
[6] T. Paing, J. Shin, R. Zane, and Z. Popovic, "Resistor Emulation Approach to Low-Power RF Energy Harvesting," Power Electronics, IEEE Transactions on, vol. 23, pp. 1494- 1501, 2008.
[7] D. Masotti, A. Costanzo, and S. Adami, "Design and realization of a wearable multi- frequency RF energy harvesting system," in Antennas and Propagation (EUCAP),
Proceedings of the 5th European Conference on, 2011, pp. 517-520.
[8] J. A. Hagerty, F. B. Helmbrecht, W. H. McCalpin, R. Zane, and Z. B. Popovic, "Recycling ambient microwave energy with broad-band rectenna arrays," Microwave
Theory and Techniques, IEEE Transactions on, vol. 52, pp. 1014-1024, 2004.
[9] Y. Kawahara, K. Tsukada, and T. Asami, "Feasibility and potential application of power scavenging from environmental RF signals," in Antennas and Propagation Society
International Symposium, 2009. APSURSI '09. IEEE, 2009, pp. 1-4.
[10] H. Nishimoto, Y. Kawahara, and T. Asami, "Prototype implementation of ambient RF energy harvesting wireless sensor networks," in Sensors, 2010 IEEE, 2010, pp. 1282- 1287.
[11] H. Rajagopalan and Y. Rahmat-Samii, "Ingestible RFID bio-capsule tag design for medical monitoring," in Antennas and Propagation Society International Symposium
147
[12] K. Opasjumruskit, T. Thanthipwan, O. Sathusen, P. Sirinamarattana, P. Gadmanee, E. Pootarapan, N. Wongkomet, A. Thanachayanont, and M. Thamsirianunt, "Self-powered wireless temperature sensors exploit RFID technology," Pervasive Computing, IEEE, vol. 5, pp. 54-61, 2006.
[13] L. Yu-Te, Y. Huanfen, B. Parviz, and B. Otis, "A 3µW wirelessly powered CMOS glucose sensor for an active contact lens," in Solid-State Circuits Conference Digest of
Technical Papers (ISSCC), 2011 IEEE International, 2011, pp. 38-40.
[14] D. J. Yeager, J. Holleman, R. Prasad, J. R. Smith, and B. P. Otis, "NeuralWISP: A Wirelessly Powered Neural Interface With 1-m Range," Biomedical Circuits and
Systems, IEEE Transactions on, vol. 3, pp. 379-387, 2009.
[15] S. Pellerano, J. Alvarado, and Y. Palaskas, "A mm-wave power harvesting RFID tag in 90nm CMOS," in Custom Integrated Circuits Conference, CICC '09. IEEE, 2009, pp. 677-680.
[16] S. Pellerano, J. Alvarado, and Y. Palaskas, "A mm-Wave Power-Harvesting RFID Tag in 90 nm CMOS," Solid-State Circuits, IEEE Journal of, vol. 45, pp. 1627-1637, 2010.
[17] R. Vyas, V. Lakafosis, A. Rida, N. Chaisilwattana, S. Travis, J. Pan, and M. M. Tentzeris, "Paper-Based RFID-Enabled Wireless Platforms for Sensing Applications,"
148
[18] N. Chaimanonart and D. J. Young, "Remote RF powering system for wireless MEMS strain sensors," Sensors Journal, IEEE, vol. 6, pp. 484-489, 2006.
[19] J. Yoo, Y. Long, L. Seulki, K. Yongsang, and Y. Hoi-Jun, "A 5.2 mW Self-Configured Wearable Body Sensor Network Controller and a 12 µW Wirelessly Powered Sensor for a Continuous Health Monitoring System," Solid-State Circuits, IEEE Journal of, vol. 45, pp. 178-188, 2010.
[20] J. Olivo, S. Carrara, and G. De Micheli, "Energy Harvesting and Remote Powering for Implantable Biosensors," Sensors Journal, IEEE, vol. 11, pp. 1573-1586, 2011.
[21] M. G. Gnoni, A. Rollo, and P. Tundo, "A smart model for urban ticketing based on RFID applications," in Industrial Engineering and Engineering Management, 2009. IEEM
2009. IEEE International Conference on, 2009, pp. 2353-2357.
[22] C. Narrijun, S. Seong-Jun, L. Jae-Youl, K. Sunyoung, K. Shiho, and Y. Hoi-Jun, "A 8 µW, 0.3-mm2 RF-powered transponder with temperature sensor for wireless environmental monitoring," in Circuits and Systems, 2005. ISCAS 2005. IEEE
International Symposium on, 2005, pp. 4763-4766 Vol. 5.
[23] U. Karthaus and M. Fischer, "Fully integrated passive UHF RFID transponder IC with 16.7µW minimum RF input power," Solid-State Circuits, IEEE Journal of, vol. 38, pp. 1602-1608, 2003.
149
[24] T. Le, K. Mayaram, and T. Fiez, "Efficient Far-Field Radio Frequency Energy Harvesting for Passively Powered Sensor Networks," Solid-State Circuits, IEEE Journal
of, vol. 43, pp. 1287-1302, 2008.
[25] F. Kocer and M. P. Flynn, "An RF-powered, wireless CMOS temperature sensor,"
Sensors Journal, IEEE, vol. 6, pp. 557-564, 2006.
[26] J. Ghalibafan and F. H. Kashani, "A circularly polarized fractal microstrip antenna for RFID applications," in Radio-Frequency Integration Technology, RFIT 2009. IEEE
International Symposium on, 2009, pp. 319-322.
[27] G. A. Vera, A. Georgiadis, A. Collado, and S. Via, "Design of a 2.45 GHz rectenna for electromagnetic (EM) energy scavenging," in Radio and Wireless Symposium (RWS),
2010 IEEE, pp. 61-64.
[28] Z. Harouni, L. Cirio, L. Osman, A. Gharsallah, and O. Picon, "A Dual Circularly Polarized 2.45-GHz Rectenna for Wireless Power Transmission," Antennas and Wireless
Propagation Letters, IEEE, vol. 10, pp. 306-309, 2011.
[29] W. Zheyu, Z. Lanlin, D. Psychoudakis, and J. L. Volakis, "Flexible textile antennas for body-worn communication," in Antenna Technology (iWAT), 2012 IEEE International
150
[30] P. J. Soh, G. A. E. Vandenbosch, S. L. Ooi, and M. R. N. Husna, "Wearable dual-band Sierpinski fractal PIFA using conductive fabric," Electronics Letters, vol. 47, pp. 365- 367, 2011.
[31] E. K. Kaivanto, M. Berg, E. Salonen, and P. de Maagt, "Wearable Circularly Polarized Antenna for Personal Satellite Communication and Navigation," Antennas and
Propagation, IEEE Transactions on, vol. 59, pp. 4490-4496, 2011.
[32] R. Jung-Sim, C. Yong-Seung, L. Jae-Hee, T. Youndo, N. Sangwook, and K. Tae Jin, "Embroidered Wearable Multiresonant Folded Dipole Antenna for FM Reception,"
Antennas and Wireless Propagation Letters, IEEE, vol. 9, pp. 803-806, 2010.
[33] T. F. Kennedy, P. W. Fink, A. W. Chu, N. J. Champagne, G. Y. Lin, and M. A. Khayat, "Body-Worn E-Textile Antennas: The Good, the Low-Mass, and the Conformal,"
Antennas and Propagation, IEEE Transactions on, vol. 57, pp. 910-918, 2009.
[34] A. Tronquo, H. Rogier, C. Hertleer, and L. Van Langenhove, "Robust planar textile antenna for wireless body LANs operating in 2.45 GHz ISM band," Electronics Letters, vol. 42, pp. 142-143, 2006.
[35] P. Salonen, K. Jaehoon, and Y. Rahmat-Samii, "Dual-band E-shaped patch wearable textile antenna," in Antennas and Propagation Society International Symposium, 2005
151
[36] H. Giddens, D. L. Paul, G. S. Hilton, and J. P. McGeehan, "Influence of body proximity on the efficiency of a wearable textile patch antenna," in Antennas and Propagation
(EUCAP), 2012 6th European Conference on, pp. 1353-1357.
[37] P. Salonen and Y. Rahmat-Samii, "Textile antennas: Effects of antenna bending on input matching and impedance bandwidth," in Antennas and Propagation, EuCAP 2006. First
European Conference on, 2006, pp. 1-5.
[38] S. Dey, N. Saha, and S. Biswas, "Design and performance analysis of UWB circular disc monopole textile antenna and bending consequences," in Antennas and Propagation
(EUCAP), Proceedings of the 5th European Conference on, 2011, pp. 1129-1133.
[39] Y. Fei and N. Soltani, "Design techniques for power harvesting of passive wireless microsensors," in Circuits and Systems, MWSCAS 2008. 51st Midwest Symposium on, 2008, pp. 289-293.
[40] A. Shameli, A. Safarian, A. Rofougaran, M. Rofougaran, and F. De Flaviis, "Power Harvester Design for Passive UHF RFID Tag Using a Voltage Boosting Technique,"
Microwave Theory and Techniques, IEEE Transactions on, vol. 55, pp. 1089-1097, 2007.
[41] N. Soltani and Y. Fei, "A High-Gain Power-Matching Technique for Efficient Radio- Frequency Power Harvest of Passive Wireless Microsystems," Circuits and Systems I:
152
[42] E. Bergeret, J. Gaubert, P. Pannier, and P. Rizzo, "Power generation system for UHF passive RFID," Electronics Letters, vol. 42, pp. 1452-1454, 2006.
[43] D. Pozar, Microwave Engineering, 2005.
[44] Hewlett-Packard Corp., "Surface Mount Microwave Schottky Detector Diodes," 1999.
[45] Skyworks Solutions Inc., Surface Mount mixer and Detector Schottky Diodes, 2010.
[46] Skyworks Solutions Inc., Data sheet - Surface Mount Mixer and Detector Schottky
Diodes, 2010.
[47] AWR Corp., "www.awrcorp.com.", 2010.
[48] Agilent Technology, Surface mount zero bias Schottky detector diodes technical data, 1999.
[49] Mega Electronics, "www.megauk.com.", 2012.
153
[51] S. Riviere, A. Douyere, F. Alicalapa, and J. D. L. S. Luk, "Study of complete WPT system for WSN applications at low power level," Electronics Letters, vol. 46, pp. 597- 598, 15/4/2010 2010.
[52] A. Douyere, J. D. Lan Sun Luk, and F. Alicalapa, "High efficiency microwave rectenna circuit: modelling and design," Electronics Letters, vol. 44, pp. 1409-1410, 2008.
[53] Hewlett-Packard Co., Linear Models for Diode Surface Mount Packages Application
Note 1124, 1997.
[54] Seiko Instruments Inc., S-882Z Series Ultra-low voltage operation charge pump IC for
step-up DC-DC converter startup, 2010.
[55] K. W. Lui, A. Vilches, and C. Toumazou, "Ultra-efficient microwave harvesting system for battery-less micropower microcontroller platform," Microwaves, Antennas &
Propagation, IET, vol. 5, pp. 811-817, 2011.
[56] P. J. Bevelacqua, "www.antenna-theory.com.", 2012.
[57] T. S. Bird, "Definition and Misuse of Return Loss [Report of the Transactions Editor-in- Chief]," Antennas and Propagation Magazine, IEEE, vol. 51, pp. 166-167, 2009.
154
[58] C. Yue-Ying, J. Yong-Chang, Z. Gang, Z. Wei, and X. Huan-Huan, "A novel compact slot antenna for broadband circularly polarized radiation," in Antennas Propagation and
EM Theory (ISAPE), 2010 9th International Symposium on, 2010, pp. 201-204.
[59] J. Pourahmadazar and S. Mohammadi, "Compact circularly-polarised slot antenna for UWB applications," Electronics Letters, vol. 47, pp. 837-838, 2011.
[60] H. A. Ghali and T. A. Moselhy, "Broad-band and circularly polarized space-filling-based slot antennas," Microwave Theory and Techniques, IEEE Transactions on, vol. 53, pp. 1946-1950, 2005.
[61] Nasimuddin, C. Zhi Ning, and Q. Xianming, "Symmetric-Aperture Antenna for Broadband Circular Polarization," Antennas and Propagation, IEEE Transactions on, vol. 59, pp. 3932-3936, 2011.
[62] M. Khalily, M. K. A. Rahim, and A. A. Kishk, "Planar Wideband Circularly Polarized Antenna Design With Rectangular Ring Dielectric Resonator and Parasitic Printed Loops," Antennas and Wireless Propagation Letters, IEEE, vol. 11, pp. 905-908, 2012.
[63] X.-y. Zhang, S. Lin, Y.-d. Wang, S.-y. Liu, X.-y. Zhang, W.-b. Zhang, and J.-x. Wang, "Broadband circularly polarized antenna with a T-type fractal boundary wide-slot and a L-shaped strip," in Microwave Conference Proceedings (CJMW), 2011 China-Japan
155
[64] H. Wang-Ta, C. Tze-Hsuan, and K. Jean-Fu, "Dual-Band Circularly Polarized Cavity- Backed Annular Slot Antenna for GPS Receiver," Antennas and Propagation, IEEE
Transactions on, vol. 60, pp. 2076-2080, 2011.
[65] J. D. Kraus, Antennas for all applications: Mcgraw Hill, 2001.
[66] I. Locher, M. Klemm, T. Kirstein, and G. Troster, "Design and Characterization of Purely Textile Patch Antennas," Advanced Packaging, IEEE Transactions on, vol. 29, pp. 777- 788, 2006.
[67] C. Hertleer, H. Rogier, L. Vallozzi, and L. Van Langenhove, "A Textile Antenna for Off- Body Communication Integrated Into Protective Clothing for Firefighters," Antennas and
Propagation, IEEE Transactions on, vol. 57, pp. 919-925, 2009.
[68] D. Schaubert and D. Pozar, "Microstrip Antennas:The Analysis and Design of Microstrip Antennas and Arrays ", 1995, pp. 57-104.
[69] D. Pozar, Schaubert, D. , Microstrip Antennas:The Analysis and Design of Microstrip
Antennas and Arrays: Wiley-IEEE Press 1995.
[70] F. Yang, Z. Xue-Xia, Y. Xiaoning, and Y. Rahmat-Samii, "Wide-band E-shaped patch antennas for wireless communications," Antennas and Propagation, IEEE Transactions
156
[71] S. D. Targonski, R. B. Waterhouse, and D. M. Pozar, "Design of wide-band aperture- stacked patch microstrip antennas," Antennas and Propagation, IEEE Transactions on, vol. 46, pp. 1245-1251, 1998.
[72] S. D. Targonski and D. M. Pozar, "Design of wideband circularly polarized aperture- coupled microstrip antennas," Antennas and Propagation, IEEE Transactions on, vol. 41, pp. 214-220, 1993.
[73] R. Bancroft, Microstrip and Printed Antenna Design: SciTech publishing, Inc., 2004.
[74] G. Yong-Xin, K. Kah-Wee, and O. Ling Chuen, "Wideband Circularly Polarized Patch Antenna Using Broadband Baluns," Antennas and Propagation, IEEE Transactions on, vol. 56, pp. 319-326, 2008.
[75] W. Kin-Lu and C. Tzung-Wern, "Single-patch broadband circularly polarized microstrip antennas," in Antennas and Propagation Society International Symposium, 2000. IEEE, 2000, pp. 984-987 vol.2.
[76] C. C. Chou, K. H. Lin, and H. L. Su, "Broadband circularly polarised crosspatch-loaded square slot antenna," Electronics Letters, vol. 43, pp. 485-486, 2007.
157
[77] N. Felegari, J. Nourinia, C. Ghobadi, and J. Pourahmadazar, "Broadband CPW-Fed Circularly Polarized Square Slot Antenna With Three Inverted-L-Shape Grounded Strips," Antennas and Wireless Propagation Letters, IEEE, vol. 10, pp. 274-277, 2011.
[78] S. Jia-Yi and C. Wei-Hung, "Axial-Ratio-Bandwidth Enhancement of a Microstrip-Line- Fed Circularly Polarized Annular-Ring Slot Antenna," Antennas and Propagation, IEEE
Transactions on, vol. 59, pp. 2450-2456, 2011.
[79] K. C. Hwang, "Broadband circularly-polarised Spidron fractal slot antenna," Electronics
Letters, vol. 45, pp. 3-4, 2009.
[80] T. Fukusako, R. Sakami, and K. Iwata, "Broadband circularly polarized planar antenna using partially covered circular wide-slot and L-probe," in Microwave Conference,
APMC 2008. Asia-Pacific, 2008, pp. 1-4.
[81] S. Jia-Yi, C. I. G. Hsu, H. Min-Hua, O. Yu-He, and W. Ming-Ting, "Design of Circularly Polarized Annular-Ring Slot Antennas Fed by a Double-Bent Microstripline," Antennas
and Propagation, IEEE Transactions on, vol. 55, pp. 3134-3139, 2007.
[82] S. Jia-Yi and W. Kin-Lu, "Bandwidth enhancement of a microstrip-line-fed printed wide- slot antenna," Antennas and Propagation, IEEE Transactions on, vol. 49, pp. 1020-1024, 2001.
158
[83] J. Pourahmadazar, C. Ghobadi, J. Nourinia, N. Felegari, and H. Shirzad, "Broadband CPW-Fed Circularly Polarized Square Slot Antenna With Inverted-L Strips for UWB Applications," Antennas and Wireless Propagation Letters, IEEE, vol. 10, pp. 369-372, 2011.
[84] S. Jia-Yi, C. I. G. Hsu, C. Zhi-Wei, and C. Chi-Chaan, "Broadband CPW-Fed Circularly Polarized Square Slot Antenna With Lightening-Shaped Feedline and Inverted-L Grounded Strips," Antennas and Propagation, IEEE Transactions on, vol. 58, pp. 973- 977, 2010.
[85] S. Jia-Yi and C. Chi-Chaan, "Circularly Polarized Square Slot Antenna With a Pair of Inverted-L Grounded Strips," Antennas and Wireless Propagation Letters, IEEE, vol. 7, pp. 149-151, 2008.
[86] C. H. Chen, E. K. N. Yung, and B. J. Hu, "Miniaturised CPW-fed circularly polarised corrugated slot antenna with meander line loaded," Electronics Letters, vol. 43, pp. 1404- 1405, 2007.
[87] V. P. Sarin, M. S. Nishamol, D. Tony, C. K. Aanandan, P. Mohanan, and K. Vasudevan, "A Broadband L-Strip Fed Printed Microstrip Antenna," Antennas and Propagation,
159
[88] A. R. El-Damak, H. Ghali, and H. F. Ragaie, "Circularly polarized fractal slot antenna," in Microwave Conference, 2005 European, 2005, p. 4 pp.
[89] Y. Sai Ho, M. Kim Fung, and C. Wing Shing, "A Bandwidth Improved Circular