NUMERICAL ANALYSIS OF HELICAL AND LOG-PERIODIC ANTENNAS FOR SHORT PULSE APPLICATIONS A THESIS IN Electrical Engineering Presented to the Faculty of the University of Missouri-Kansas City in partial fulfillment of the requirements for the degree MASTER OF SCIENCE by WALEED AL-SHAIKHLI B.S., University of Missouri – Kansas City, 2018 Kansas City, Missouri 2020 © 2020 WALEED AL-SHAIKHLI ALL RIGHTS RESERVED NUMERICAL ANALYSIS OF HELICAL AND LOG-PERIODIC ANTENNAS FOR SHORT PULSE APPLICATIONS Waleed K. Al-Shaikhli, Candidate for the Master of Science Degree University of Missouri – Kansas City, 2020 ABSTRACT The planar log-periodic (LP) and helical antennas are numerically studied as two antennas with a wide range of applications. The advantages of the LP antenna are the large adjustable bandwidth as a frequency independence radiator, its low profile, and that it can be made to be elliptically polarized. The main advantages of a helical antenna are its excellent power handling capability and tunable gain. The helical antenna is widely used in many UWB applications such as Radar, satellite communication, GPS, and other short-pulse applications. High far-field gain is essential to many applications, but a tradeoff between gain, and time- domain dispersion exists if the input of the helical antenna is to consist of short-pulses. To quantify the level of dispersion, the antennas considered in this work are modeled as linear systems, and their time-domain impulse response is calculated using CST Microwave time- domain and FEKO frequency-domain simulations of the structure. A comprehensive parametric study of the helical antenna is conducted in FEKO followed by a multigoal optimized design of an L band helical antenna to minimize pulse dispersion, size, and input impedance while maximizing far-field gain and pulse shape preservation. iii APPROVAL PAGE The faculty listed below, appointed by the Dean of the School of Computing and Engineering have examined a thesis titled “Numerical Analysis of Helical and Log-periodic Antennas for Short Pulse Applications,” presented by Waleed Al-Shaikhli, candidate for the Master of Science degree, and certify that in their opinion it is worthy of acceptance. Supervisory Committee Ahmed M. Hassan, Ph.D., Committee Chair Department of Computer Science & Electrical Engineering Deb Chatterjee, Ph.D. Department of Computer Science & Electrical Engineering Anthony Caruso, Ph.D. Department of Physics and Astronomy Mahrukh Khan, Ph.D. Department of Computer Science & Electrical Engineering iv TABLE OF CONTENTS ABSTRACT ................................................................................................................. iii LIST OF ILLUSTRATIONS ............................................................................................ viii LIST OF TABLES .......................................................................................................... xi LIST OF ABBREVIATIONS ............................................................................................xii ACKNOWLEDGMENTS............................................................................................... xiii 1. Antenna Introduction and Definitions ......................................................................... 1 Motivation for Work .................................................................................................................. 1 The Antenna Concept ................................................................................................................ 1 Antenna Figures-of-Merit .......................................................................................................... 2 Field Regions .............................................................................................................................. 8 Antennas in Short-Pulse Systems............................................................................................... 9 Friis transmission equation ...................................................................................................... 11 Survey of Antennas for Short Pulse Applications ..................................................................... 12 Summary.................................................................................................................................. 15 2. Performance Analysis for Short Pulse Applications ................................................... 16 UWB Signals ............................................................................................................................ 17 Frequency Domain Performance ............................................................................................. 19 Group Delay ............................................................................................................................. 21 Fidelity Factor .......................................................................................................................... 22 Time Domain Performance ...................................................................................................... 24 Summary.................................................................................................................................. 27 v 3. The Log Periodic Antenna ......................................................................................... 28 Frequency Independent antennas ........................................................................................... 28 The Planar Log-Periodic Antenna ............................................................................................ 29 Design of a Planar Log-Periodic for Short pulse-UWB Applications ........................................ 33 Size and Polarization improvement of a Planar Log-Periodic .................................................. 38 Summary.................................................................................................................................. 41 4. The Helical Antenna ................................................................................................. 42 Modes of Operation................................................................................................................. 43 Helical Antenna Applications ................................................................................................... 44 Antenna Validation .................................................................................................................. 45 Helical Antenna Literature Review .......................................................................................... 47 Summary.................................................................................................................................. 48 5. Design and Parametric Analysis of A Helical Antenna ................................................ 49 Antenna Design ....................................................................................................................... 49 Ground Plane Size .................................................................................................................... 53 Wire Diameter ......................................................................................................................... 55 Helix Turns ............................................................................................................................... 57 Dielectric Rod ........................................................................................................................... 62 Impedance Matching ............................................................................................................... 67 Summary.................................................................................................................................. 76 6. Helical Antenna Optimization ................................................................................... 77 vi Antenna Optimization ............................................................................................................. 77 Summary.................................................................................................................................. 84 7. Conclusion and Future Work..................................................................................... 85 References ............................................................................................................... 87 VITA ......................................................................................................................... 95 vii LIST OF ILLUSTRATIONS FIGURE PAGE Figure 1. Antenna 2D field pattern ........................................................................................... 2 Figure 2. Reflection, dielectric and ohmic losses ...................................................................... 7 Figure 3. Friis Equation ........................................................................................................... 11 Figure 4. Example of UWB signal in the (a) time-domain (b) and frequency domain ............ 18 Figure 5. Frequency-domain system link-level characterization [5] ...................................... 19 Figure 6. UWB system link-level characterization in the time-domain [5]. ............................ 24 Figure 7. Planar Log-periodic .................................................................................................. 30 Figure 8. 2-Arm Log-Periodic Antenna ...................................................................................