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The Utilization of Software Defined Radios for Adaptive, Phased Array Antenna Systems University of Vermont ScholarWorks @ UVM Graduate College Dissertations and Theses Dissertations and Theses 2020 The Utilization of Software Defined Radios for Adaptive, Phased Array Antenna Systems Evan Fennelly University of Vermont Follow this and additional works at: https://scholarworks.uvm.edu/graddis Part of the Electrical and Electronics Commons Recommended Citation Fennelly, Evan, "The Utilization of Software Defined Radios for Adaptive, Phased Array Antenna Systems" (2020). Graduate College Dissertations and Theses. 1299. https://scholarworks.uvm.edu/graddis/1299 This Thesis is brought to you for free and open access by the Dissertations and Theses at ScholarWorks @ UVM. It has been accepted for inclusion in Graduate College Dissertations and Theses by an authorized administrator of ScholarWorks @ UVM. For more information, please contact [email protected]. The Utilization of Software Defined Radios for Adaptive, Phased Array Antenna Systems A Thesis Presented by Evan Michael Fennelly to The Faculty of the Graduate College of The University of Vermont In Partial Fulfillment of the Requirements for the Degree of Master of Science Specializing in Electrical Engineering October, 2020 Defense Date: August 27th, 2020 Thesis Examination Committee: Jeff Frolik, Ph.D., Advisor Adrian Del Maestro, Ph.D., Chairperson Tian Xia, Ph.D. Cynthia J. Forehand, Ph.D., Dean of Graduate College Abstract The increased use of internet of things (IoT) devices will result in them being deployed in a wide variety of environments and therefore warrant antenna systems that can be adapted to improve link performance. Flexible communication technologies allow for increased throughput, reliability, and improved efficiency in wireless channels. This can be accomplished by implementing phased array antennas, among others. Phased arrays create a beam that can be steered electronically, but are expensive to implement given the many phase precise hardware components that need to be adjustable. A software defined radio approach to beamforming can reduce this complexity for each array adaptation, if made in software. This thesis leverages software defined radio (SDR) for the purpose of phase mea- surements and beamforming. A phase measurement system was created in GNU Radio to determine phase differences between SDRs. This algorithm was tested on a direction-finding system measuring the angle of arrival of a moving transmitter. In addition, transmit beamforming was implemented via SDR on a tripolar array and a four-element patch antenna array. Through simulation, the tripolar array has an ∼3 dB improvement in gain over a single monopole antenna in azimuth. The measured antenna patterns did not match the simulation, but the reconfigurability of the SDR platform provided the ability to correct the nonidealities in the physical antenna. The azimuth test results show that beamsteering can be accomplished with a median power increase of 3 dB over the omnidirectional beamsteering case. The patch antenna array was tested by simulating a Butler matrix, a beamforming net- work typically implemented in hardware. The array pattern had a 3 dB beamwidth of ∼22° in simulation and ∼20° through testing, with a maximum steering error of ∼3° across the four Butler cases. The presented validation of the phase measurement and beamforming systems is promising for future work in the realm of beamforming via software defined radio. Acknowledgements First, I would like to thank my advisor Dr. Jeff Frolik. Throughout my last 5 years at UVM as an undergrad and graduate student, he has been an excellent professor and mentor and has thoroughly prepared me for my future as an engineer. I would like to thank Dr. Tian Xia and Dr. Adrian Del Maestro for taking the time to serve on my thesis committee. I would also like to thank Tim Laracy. It was a pleasure working with him every day since the start of senior year. Additionally, I must acknowledge the rest of the AMP crew for all of their help, motivation and for the levity they brought to our work. Finally, I would like to thank my family for their constant love and support. Colin and Annie, thank you for keeping me grounded and being my best friends. Mom and Dad, thank you for pushing me to be my best and helping through the many challenges I faced as a college student. Thank you. ii Table of Contents Acknowledgements . ii List of Figures . vii List of Tables . viii 1 Introduction 1 1.1 Motivation . .1 1.2 Background . .2 1.2.1 Phased Arrays . .3 1.2.2 Software Defined Radio . .4 1.3 Problem Statement . .5 1.4 Contributions . .5 1.5 Thesis Outline and Research Approach . .7 2 Antenna Arrays and Software Defined Radio 8 2.1 Antenna Arrays . .9 2.1.1 Phased Arrays and Beamforming . 10 2.1.2 Angle of Arrival Detection . 13 2.2 Software Defined Radio . 16 2.2.1 SDR Hardware . 16 2.2.2 SDR Hardware Examples . 17 2.2.3 GNU Radio Software . 19 2.3 Related Prior Work . 20 2.3.1 Angle of Arrival via Software Defined Radio . 21 2.3.2 Beamforming via Software Defined Radio . 22 2.4 Conclusion . 24 3 Software Defined Radio Phase Calibration 25 3.1 Phase Synchronization . 25 3.2 Methods . 27 3.3 Cross Correlation Phase Measurement . 30 3.4 Test Results . 31 3.4.1 Phase Measurements . 32 3.4.2 Angle of Arrival Measurements . 34 3.5 Beamforming Utilizing GNU Radio . 36 3.6 Conclusion . 37 iii 4 Tripolar Antenna Beamforming 39 4.1 Introduction . 40 4.2 Antenna System Model . 41 4.3 Omnidirectional Results . 43 4.3.1 Single Monopole Antenna . 43 4.3.2 Tripolar Antenna . 44 4.4 Beamsteering Results . 44 4.4.1 Azimuth (φ) Steering . 44 4.4.2 Elevation (θ) Steering . 46 4.5 Test Results . 48 4.6 Conclusion . 53 5 Patch Antenna Array 55 5.1 Patch Antenna Design . 56 5.2 Array Simulation Results . 61 5.2.1 Butler Matrix Comparison . 63 5.2.2 Digital Beamsteering . 65 5.3 Array Test Results . 66 5.4 Conclusion . 71 6 Conclusions and Future Work 72 6.1 Contributions . 72 6.2 Future Work . 74 6.2.1 Tripolar Antenna Beamforming Pattern Characterization . 74 6.2.2 Flexible Antenna Array Performance . 75 6.2.3 Transmit Beamforming with USRP SDR Platform . 76 6.3 Final Words . 77 Biblography 79 A Source Code 83 A.1 Phase in GNU Radio . 83 A.1.1 Phase Measurement . 83 iv List of Figures 1.1 Diagram of phased array elements transmitting, illustrating the signal splitting from the source and the phase being modified by the (φ) blocks [1] . .3 2.1 Transmit and receive antenna array diagram with multiple transmit (TX) and receive (RX) elements, also known as a multiple input, mul- tiple output (MIMO) configuration . .9 2.2 Phase steering diagram [2] . 12 2.3 Normalized array factor at boresight of a ULA with an element spacing of d = λ/2 for 8, 16, and 32 elements [2] . 13 2.4 Angle of arrival phase delay diagram [3] . 14 2.5 Flow graph of a typical SDR transmitter [4] . 17 2.6 Flow graph of a typical SDR receiver [4] . 17 2.7 A basic GNU Radio block diagram. A signal source, osmocom sink and QT GUI time sink are used. 20 2.8 Software defined radio phased array implementation with USRP N210 SDR [5] . 23 2.9 Distributed beamforming general architecture [6] . 23 3.1 The random phase offset as measured on an oscilloscope for three dif- ferent instances of the SDRs beginning to transmit. The phases in the top, middle and bottom plots versus the desired 90° are -160°, -40° and 85° respectively. 26 3.2 Phase feedback block diagram using an external splitter to feedback the signal for phase correction . 27 3.3 Noisy BladeRF feedback signal . 28 3.4 Simulated phase measurement with an SNR of 14 dB. The top plot is the result of the cross correlation and the bottom plot is the real and imaginary values of the two signals being tested. The calculated phase shift is at the bottom. 32 3.5 Simulated phase measurement with an SNR of 0 dB. The top plot is the result of the cross correlation and the bottom plot is the real and imaginary values of the two signals being tested. The calculated phase shift is at the bottom. 33 3.6 AoA test diagram . 34 3.7 AoA test results with a median phase error of 3.5° ........... 35 v 3.8 GNU Radio block diagram used for tripolar beamforming. The fast multiply constant blocks modify the phase and are controlled by the user through the QT GUI range blocks. The osmocom sink blocks control the SDR hardware. 37 3.9 GNU Radio GUI used for phase shift control. The user can control the phase shift between SDRs by changing the phase using the sliders. 37 4.1 Tripolar antenna model integrated with commercial wireless sensor node (courtesy: Univ. of Vermont) . 40 4.2 Tripolar Antenna model in HFSS which contains three ∼ λ/4 monopole antennas at 2.4 GHz . 42 4.3 Single monopole and omnidirectional tripolar, azimuth comparison (XY plane) . 43 4.4 Three of the twelve sectors enabled by the tripolar beamsteering in azimuth (XY plane). The maximum gain is 4.74 dB. 46 4.5 Beamsteering in Elevation (θ) with φ = 90° (YZ plane) . 47 4.6 Tripolar antenna model . 49 4.7 Antenna test setup . 49 4.8 Tripolar beamsteering: 0° case . 50 4.9 Tripolar beamsteering: 120° case . 50 4.10 Tripolar beamsteering: 240° case . 50 4.11 “Omnidirectional” pattern: HackRF vs. signal generator comparison 51 4.12 “Omnidirectional” pattern with phase correction (0°, 120°,0°)..... 52 4.13 “Omnidirectional” pattern: HackRF (max: -40 dBm) vs.
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