ACTIVE ANTENNA AND CIRCUITS FOR UWB TRANSCEIVERS

Transcription

1 ACTIVE ANTENNA AND CIRCUITS FOR UWB TRANSCEIVERS MITHILESH KUMAR CENTRE FOR APPLIED RESEARCH IN ELECTRONICS (CARE) INDIAN INSTITUTE OF TECHNOLOGY, DELHI December 2010

2 ACTIVE ANTENNA AND CIRCUITS FOR UWB TRANSCEIVERS MITHILESH KUMAR Centre for Applied Research in Electronics (CARE) Submitted in fulfillment of the requirement of degree of Doctor of Philosophy to the INDIAN INSTITUTE OF TECHNOLOGY, DELHI December 2010

3 Dedicated to my parents Shri Madan Mohan Ms Keshar Devi

4 CERTIFICATE This is to certify that the thesis "Active Antenna And Circuits For UWB Transceivers", being the submitted by Mr. Mithilesh Kumar for the award of the degree of Doctor of Philosophy (Ph.D.) to the Indian Institute of Technology Delhi, New Delhi, is a record of original bonafide research work carried out by him under our guidance and supervision. The results contained in thesis have not been submitted in part or full to any other university or institute for the award of any degree or diploma. We certify that he has pursued the prescribed course of research. ANANJAN BASU Associate Professor Centre for Applied Research in Electronics (CARE) Indian Institute of Technology, Delhi , INDIA SHIBAN K. KOUL Professor Centre for Applied Research in Electronics (CARE) Indian Institute of Technology, Delhi , INDIA

5 ACKNOWLEDGEMENTS I reserve my deep sense of gratitude and sincere thanks to my Supervisor Prof. Shiban K. Koul, Professor, Centre for Applied Research in Electronics (CARE). Indian Institute of Technology (IIT), Delhi for giving me opportunity to work in the esteemed Institute. With immense pleasure, I sincerely thank his avid counseling, immense cooperation, encouragement and the welcoming support, he has always rendered throughout towards accomplishing this task. I thank him for instilling in me the right attitude towards research. His guardianship and sincerity are beyond the scope of acknowledgement. My sincere gratitude is towards my Supervisor Dr. Ananjan Basu, Associate Professor, CARE, IIT Delhi, for his most encouraging attitude, vision, constant support, and critical evaluation rendered to me throughout the entire phase of present work. It was his great support that helped me to achieve confidence in experimentation and modeling. I take immense pleasure in expressing my sincere thanks and gratitude to Dr. Mahesh P. Abegaonkar, Assistant Professor, CARE, IIT Delhi for continuous guidance and encouragement. I express my sincere thanks to Prof. Ranjan Bose, Professor, Electrical Engineering Department, IIT Delhi for providing me testing facilities in his laboratory. My sincere thanks are due to my colleagues Ms. Preeti Sharma, Mr. Manoj Singh Parihar, and Mr. Madhur Deo Upadhayaya, and M.Tech. students Mr. Meenakshi Sundarm, Mr. Prasun Choungder, Shiva, Lalithendra, Pramod and Kinjal of RF & Microwave laboratory, CARE for their constant support in various ways. I also thank fellow friends of my department and outside, Mr. Ramswroop Meena, Mr. R.K.Bayal, 111

6 and all other research scholars of CARE with whom I shared my thoughts during my stay at IIT Delhi. I thankfully acknowledge technical support and cooperation of Mr. S.P. Chakraborty in various ways during Ph.D. experimentation phase and personnel guidance as elder brother. Support from Mr. Ashok and Mr. Pradeep Saxena (Workshop) is greatly felt and duly acknowledged. I also would like to acknowledge the Department of Electronics Engineering, University College of Engineering, Rajasthan Technical University, Kota, Rajasthan, for permitting me to avail the QIP study leave. Finally saving the best for the last, "my family". It would be belittling to express the boundless love, affection and encouragement received from my father, Shri Madan Mohan, and my mother Ms. Kesher Devi. I cannot finish without mentioning my wife Sheela, who has been offering all round support during the period of my study. (MITHILESH KUMAR) iv

7 ABSTRACT This thesis deals with the analysis, modeling, design, and development of novel antennas and circuits for Ultra-Wide-Band (UWB) transceivers. The circuits referred to comprise UWB signal generation circuits and UWB printed antennas, which combine to give complete UWB transmitters. The antenna by itself is also a rudimentary UWB receiver. This work focuses on UWB systems based on information-bearing ultra-short low-power pulses. The work was motivated by the absence of simple UWB generating circuits that can be assembled using off-the-shelf devices and low-cost technologies, as is possible for conventional microwave amplifiers and mixers. Currently UWB systems (with some exceptions) requires either sophisticated pulse generating equipment (comparable to a microwave synthesized source) or quite complex IC's made using state-of-the-art MMIC/RFIC processes. Circuits using step-recovery diodes have also been reported, but such diodes are MMIC/RFIC incompatible. Filling in this gap may be taken as the basic problem statement of this Ph.D. thesis. This thesis presents a new UWB signal generation technique using a single phemt as an active device, which will be useful for UWB communication. Initially a novel and simple method to generate short pulses is demonstrated at low frequency to verify the proposed scheme. At low frequencies, the phemt can be regarded as an ideal switch and the reactive elements as ideal inductors and capacitors without parasitics. Under these conditions analytical results are meaningful, and a complete analysis of the UWB signal generation process carried out is presented. The design and development of UWB signal generation circuits for the frequency band GHz is then described. At these frequencies, analytical approaches are not useful, and we rely V

8 on circuit simulations. The proposed circuit was simulated using Agilent ADS2009 simulation software and then fabricated on a soft substrate (make Nelco, Er = 3.2, thickness = 0.25 mm). The simulated and measured results show good agreement. Two types of circuits have been demonstrated. In the simpler circuit UWB pulses are generated both at rising and falling edges of the input pulses (the binary data stream which is to be transmitted). In many cases, only one pulse (say at the falling edge of the input) is required at the output. We have demonstrated a novel circuit with an additional diode that achieves this. To fabricate this circuit using printed elements, a lumped inductor is realized using a microstrip transmission line and a capacitor is realized in parallel-plate or inter-digitated form. The output pulse-shape is found to be quite insensitive to the rise and fall times of the input. The fabrication and testing of this circuit has been described in detail in this thesis. It is seen that the main pulse occupies 0.5 ns in time domain and roughly the prescribed bandwidth of 3 10 GHz in frequency domain. Even counting the small ringing in the pulse, the duration is < 1.5 ns, which is more than satisfactory for data transmission at 500 Mbps. As in conventional wireless communication systems, an antenna also plays a crucial role in UWB systems. However there are more challenges in designing a UWB antenna than a narrow-band one. A suitable UWB antenna should be capable of operating over an ultra-wide bandwidth as allocated by the FCC-USA and other regulatory bodies. At the same time, satisfactory (typically constant) radiation patterns over the entire frequency range are also necessary. Another requirement of the UWB antenna is good time domain performance, i.e. a short inter-antenna impulse response with minimal dispersion. The first type of antenna studied in this thesis is the microstrip-fed printed monopole antenna. The second type of UWB antenna is the conventional slot antenna, also fed by a microstrip line. The performance and vi

9 characteristics of UWB monopole and slot antenna are investigated in both frequency domain and time domain. It has been demonstrated numerically and experimentally that both types of antennas are suitable for UWB applications, but there are important differences and novel features that have not been recognized till now. The final part of our work is devoted to combining the circuits and antennas into a UWB `active integrated antenna'. The radiated UWB pulses are measured in frequency and time domain to investigate the active UWB antenna behavior. The proposed antenna acts as a filter that tailors the spectrum of the transmitted pulse to a shape close to that recommended for UWB communications. The work reported in this thesis should help in developing simple easy-toassemble UWB pulse generation and transmission schemes using off-the-shelf components. These sub-circuits can be further combined with standard receiver components such as low-noise amplifiers, mixers and signal processing blocks to develop complete UWB communication systems. Details of this type of UWB system development fall in the domain of signal processing and have not been addressed here. The UWB pulse generation circuit demonstrated is, to the best of our knowledge, the simplest known for generating UWB pulses, is low cost and is compatible with MMIC (and RF-CMOS if a diode is not required), which is important for practical UWB systems. It is hoped that some of the future UWB communication systems that include antenna arrays, multiple transmitters and appropriate receivers, will be developed using the sub-systems presented here. vii

10 CONTENTS I Certificate of Supervisors i II Acknowledgements iii III Abstract v IV Contents ix V List of Figures xiii VI List of Abbreviations xx CHAPTER 1 Review and Scope of Thesis 1.1 Introduction Brief History of UWB Technology UWB Definition Spectral Mask UWB Pulse Shape UWB Modulation Methods Multipath Key Benefits of UWB Application of UWB Technology Communications and Sensors Position Location and Tracking Radar Electronic Components for UWB Systems UWB Signal Generation Circuits UWB Antennas UWB Active Antenna 17

11 1.5 Problem Statement Scope and Organization of Thesis 18 CHAPTER 2 Simulation and Practical Investigation of Short Pulse Generation Circuits at Low Frequency 2.1 Introduction Short Pulse Generation at Low Frequency 23 using FET 2.3 Analysis of Short Pulse Generation Circuit 24 using FET FET in Turned-on State FET in Turned-off State Short Pulse Generation at Falling Edge of 32 Input alone using FET 2.5 Fabrication and Testing of Short Pulse Generation 36 Circuit at Low Frequency using FET 2.6 Conclusions 40 CHAPTER 3 UWB Signal Generation Circuits using BJT and HEMT 3.1 Introduction Generation of UWB Pulse using HEMT Fabrication and Testing of Pulse Generation 45 Circuit using HEMT 3.4 Analysis of UWB Pulse Generation 50 using HEMT 3.5 Implementation in MMIC and CMOS-RF Conclusions 54 x

12 CHAPTER 4 Improved Circuit for Generation of UWB Pulses for GHz Range 4.1 Introduction Modified Scheme to Generate UWB Signal Fabrication and Testing of Modified Scheme Spectrum of the Generated Pulse Effect of Fall Time of Input Conclusions 72 CHAPTER 5 Planar UWB Antennas and Active Antennas 5.1 Introduction Criteria for Judging the Performance of a UWB 74 Antenna 5.3 Recent UWB Antenna Developments Hexagonal Monopole Circular UWB Microstrip Antenna (With 86 Off-Center Annular Ring Slot) Circular UWB Microstrip Antenna (with concentric 90 annular ring slot) 5.4 Investigation of Traditional Microstrip Fed Slot 93 Antenna for UWB Applications 5.5 Active UWB Antenna Conclusions 109 CHAPTER 6 Conclusions and Future Scope 6.1 Summary of the Thesis Future Scope 111

13 Appendix Appendix References 134 Bibliography 140 List of Publications 148 Brief Bio-Data of Author 151 Xll