Monopole Antennas Melvin M. Weiner (retired) The MITRE Corporation Bedford, Massachusetts, U.S.A. MARCEL DEKKER, INC. NEW YORK • BASEL Copyright © 2003 Marcel Dekker, Inc. Marcel Dekker, Inc , and the author make no warranty with regard to the accompanying software, its accurac> or its suitability for any purpose other than as described in the preface This software is licensed solely on an 'as is' basis The only warranty made with respect to the accompanying software is that the diskette medium on which the software is recorded is free of defects Marcel Dekker, Inc , will replace a diskette found to be defective if such defect is not attributable to misuse by the purchaser or his agent The defective diskette must be returned within 10 days to Customer Service, Marcel Dekker, Inc,PO Box 5001 Cimarron Road Monticello, NY 12701 (914)796-1919 Library of Congress Cataloging-in Publication Data A catalog record for this book is available from the Library of Congress ISBN: 0-8247-0496-7 This book is printed on acid-free paper Headquarters Marcel Dekker, Int , 270 Madison Avenue, New York, NY 10016 tel 212-696-9000 fax 212-681-4140 Eastern Hemisphere Distribution Marcel Dekker AG Hutgasse 4, Postfach 8 1 2, CH-4001 Basel, Switzerland tel 41-61-260-6300 fax 41-61-260-6333 World Wide Web http //www dekker com The publisher otters discounts on this book when ordered m bulk quantities For more information write to Special Sales/Professional Marketing at the address below Copyright © 2003 by Marcel Dekker, Inc. All Rights Reserved. Neither this book nor any part may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, microfilming, and recording, or by any information storage and retrieval system, without permission in writing from the publisher Current printing (last digit) 10 9 8 765 43 21 PRINTED IN THE UNITED STATES OF AMERICA Copyright © 2003 Marcel Dekker, Inc. in memory of Jack H. Richmond (1922-1990) Piofessor Emeritus, The Ohio State University and James R. Wait (1924-1998) Regents Professor, University of Arizona Copyright © 2003 Marcel Dekker, Inc. Preface The primary intent of this book is to provide an industry standard for the modeling, testing, and application of airborne and ground-based monopole antennas. This standard is intended for engineers, scientists, practitioners, and students in the communication, radar, navigation, and government service industries. Most of the book is based on the original state-of-the-art work performed by the author at The MITRE Corporation in Bedford, Massachusetts with sponsorship by the U.S. Air Force and MITRE Independent Research Program. I did the work on surface-wave fields in Sec. 9.3 after my retirement from MITRE. Part I is concerned with monopole antennas in free space. In this part of the book Earth parameters do not affect the antenna's electrical properties but do affect propagation losses (denoted as basic transmission loss Lb(d) in Eq. (6.4.1)). This characteristic is realized if the base of the antenna is more than a quarter- wavelength above the earth's surface. The propagation mode is assumed to be the sum of direct and indirect waves through the troposphere by line of sight, reflection, refraction, and/or scattering—a typical mode and paths at frequencies above 30 MHz (see Sec. 6.5). An overview of the models, numerical results, applications, and computer programs in Part I is given in Chapter 1. Part II is concerned with monopole antennas in proximity to flat earth. In Part II, Earth parameters do affect the antenna's electrical properties This Copyright © 2003 Marcel Dekker, Inc. vi Preface characteristic is realized if the base of the antenna is below the earth's surface or within a quarter-wavelength above the earth's surface Propagation modes are assumed to be a space wave within the radio horizon (with no earth dependent propagation losses), a space wave over the horizon by reflection from the ionosphere (with no earth-dependent propagation losses but with ionospheric propagation losses), or a surface wave through the earth (with earth-dependent propagation losses)—typical modes and paths at frequencies below 30 MHz (see discussion preceding and following Eq (131 3)) An overview of the models, numerical results, applications and computer programs in Part II is gi\en in Chapter 7 This book is a greatly expanded version of an earlier book (MM Weiner, SP Cruze, CC Li, and WJ Wilson, Monopole Elements on Cucular Ground Planes, Norwood, MA Artech House, 1987) that was restricted to discussion of structures in free space only The present book discusses structures in proximity to flat earth in addition to those in tree space Chapters 1-5 and Appendices A 1 -A 5, and B 1-B "5 are partially revised from the previous book except that the computer programs in Appendices B 1 -B 5 are now provided on CD rather than as program printouts Entirely new material is in Chapters 6-13 and Appendices A 6-A 8, B 6-B 12, C and D Although the monopole antenna is one of the oldest of antennas, its properties are neither well understood nor standardized, particularly for ground- plane radii that are small or comparable to a wavelength Most treatments idealize the monopole antenna by assuming a ' perfect" ground plane (of infinite extent and conductivity) Other treatments utilize asymptotic models that give approximate results only In this book, these deficiencies are addressed by providing an in depth treatment oi the influence of both the finite extent and proximity to earth of the ground plane State of the art numerical methods, including Richmond s method of moments for disk ground planes and Lawrence Eivermore Laboratory s Numerical Electromagnetics Code for radial-wire ground planes are featured to provide accurate results and an industry standard that were previously unavailable for monopole antennas A vertical cylindrical monopole element at the center of a horizontal circular ground plane has the simplest monopole antenna geometry because its structure and radiation pattern are both invariant m the azimuthal direction Such a structure is convenient for modeling, testing, and standardization The electrical properties of monopole antennas with nonperfect ground planes in free space can be substantially different from those with a perfect ground plane For perfectly conducting structures in free space, the radiation efficiency is 100% However edge diffraction by the ground plane can reduce the input resistance (equal to the radiation resistance) by a factor of two peak directivity b> as much as 3 3 dB and directivity in the plane of the ground plane by as much as 3 3 dB and increase the magnitude of the input reactance by an Copyright © 2003 Marcel Dekker, Inc. Preface vii infinite percentage from the value for a perfect ground plane (see Table 4 in Sec. 4.5). Furthermore, the direction of peak directivity can be tilted as much as 58 degrees above the plane of the ground plane compared with zero degrees for a perfect ground plane (see Fig. 5 in Sec. 4.5 and Table A2-22 in App. A.2). Those same structures in proximity to earth can be substantially different from those in free space and from those with a perfect ground plane. Fresnel reflection causes a directivity null of minus infinity dB in the plane of the ground plane (see App. A.8). An electrically short monopole element in close proximity to dielectric earth can have a radiation efficiency of almost 0% and a peak directivity below earth of approximately +15 dB at a critical angle of approximately 20 degrees from the nadir direction (see Fig. 75 in Sec. 9.2.2 and Figs. 76 and 77 in Sec. 9.2.3). For quarterwave elements on electrically small ground planes resting on most types of earth except sea water, the peak directivity in the High Frequency (HF) band is not substantially different from that of a perfect ground plane but is tilted approximately 30 degrees above the plane of the ground plane compared to 0 degrees for a perfect ground plane (see Fig. 91 in Sec. 10.2 4) The input impedance is not as severely affected by edge diffraction (because the earth softens the edge of the ground plane) but is now affected by the decreased radiation efficiency (see Figs. A6-57 and A6-58 in Appendix A.6). Part I is based on work performed for the U.S. Air Force SINCGARS radio program. The radio is a frequency-hopping antijamming radio in the Very High Frequency (VHP) band and utilizes an electrically short antenna to minimize aerodynamic drag on airborne platforms. The development of optimally efficient, electronically tunable antennas for this radio is of interest. Although the antenna ground plane is platform-dependent, it is usually small compared with a radio frequency (RF) wavelength. A circular ground plane provides a standardized ground-plane geometry with which to model and evaluate candidate antennas. Accordingly, a VHP antenna range with an eight-foot diameter ground plane was constructed at The MITRE Corporation and a theoretical study was initiated to evaluate candidate antennas. The system margin parameters of the SINCGARS radio were also investigated. The results are reported in technical reports ESD-TR-86-241, ESD-TR-85- 136, ESD-TR-88-270, and ESD-TR-82-400 prepared by MITRE for the Electronic Systems Division, Air Force Systems Command, Hanscom Air Force Base, Massachusetts under Project 6480, Contracts F19623-82-C-0001, F19628- 84-C-0001 and F19628-86-C-0001. The book Monopole Elements on Circular Ground Planes and the present book's Chapters 1-5, Apps. A.1-A.5, and Apps. B.1-B.6 are from report ESD-TR-86-241. Sections 6.3, 6.4, and 6.5 are from reports ESD-TR-88-270, ESD-TR-85-136, and ESD-TR-82-400, respectively. Sec. 6.1 is from MITRE report M90-93 prepared under the MITRE Independent Research Program, Project 91260. Copyright © 2003 Marcel Dekker, Inc. viii Preface Part II is based on work sponsored by the MITRE Independent Research Program, Project Nos 91260 91030, and 91740, in support of the Advanced Over-the-Honzon (AOTH) radar program of the Defense Advanced Research Project Agency (DARPA) and the U S Air Force The proposed radar operates in the HF band with over-the-honzon space wave mode of propagation made possible by reflection from the ionosphere It would utilize a ground-based receiving array comprising hundreds or thousands of randomly spaced antenna elements Although an array with electrically large ground planes is desirable to increase radiation efficiency and reduce the elevation angle of peak directivity, they are prohibitively expensive to construct and maintain One approach is to use elements with electrically small ground planes A monopole element at the center of a circular ground plane provides a standardized geometry tor evaluating candidate elements and ground planes Accordingly, a theoretical study was initiated to understand the electrical properties of monopole elements with circular ground planes in proximity to earth The results are reported in MITRE reports MTR-10989 (Project 91260), M90-92 (Project 91260), M91-104 (Project 91030), MTR-92B0000089 (Project 91260), MTR 92B0000090 (Project 91260), MTR-11277 (Project 91030), MTR-11278 (Project 91030), MTR-11169 (Project 91030), MTR-93B000016 (Project 91740), and M91 -82 by LW Parker (Project 91260) Sec 9 is in part from MTR-11277, Sec 10 and App A 6 are from M90 92, MTR-92B0000089, and MTR-92B0000090 Sec 11 and App A 7 are from M91-104 and MTR-11278, part of Sec 12 is from M91-82, Sec 131 is from MTR-10989 and MTR-93B0000169, Sec 132 is from MTR-11169, and Sec 133 is from MTR-11277 The above technical reports are in the public domain and are obtainable from the National Technical Information Service (NTIS) The discussion of surface waves in Sec 9 3 represents new work I performed specifically for this book It includes approximate expressions for the case when the index of refraction is approximately unity, complementing work of earlier investigators for the case when the index of refraction is large Melvm M Wemer Copyright © 2003 Marcel Dekker, Inc. Acknowledgments Several MITRE technical staff members and cooperative students contributed to this work. SP Cruze contributed to Sec. 3.5, wrote program LEITNER-SPENCE in App. B.03, and performed some of the early modeling m Sec. 6.3. CC Li contributed to Sec. 4.2, edited programs RICHMONDl and RICHMOND2 in App. B.02, program AWADALLA in App. B.05, and wrote program BARDEEN in App. B.04. WJ Wilson contributed to Sec. 2 3 and Sec. 3.3. JE Kriegel derived the correct form of the continued fractions given in Eqs. (3.5.4) and (3 5.5), contributed to the evaluation of the limits in Eqs. (3.3.22- 3.3.24), and confirmed the partial differential equation solution given in Eq. (C-27b). WC Corrieri (deceased) skillfully performed the measurements discussed m Chapter 5. K Pamidi contributed to the development of Eq. (3.3.16). LW Parker (deceased) developed the program for the computer plots in Sec. 6.1 and contributed Sec. 12.3.2. CR Sharpe obtained the computer plots in Sec. 6.1 and edited the R1CHMOND3, RICHMOND4, RICHMOND5, RICHMOND6, and WAIT-SURTEES programs in App. B.06 and B.09- B.10. G Ploussios directed the design and development of electronically tuned helical monopole elements discussed in Sec. 6.2.9 and contributed Fig. 38. RD Parsons wrote the computer program SONF which produced the numerical results m Sec 6 4. C Korbani and SF McGrady wrote the computer program that produced the numerical results in Sec. 6.3. E Jappe and NJ Johnson ix Copyright © 2003 Marcel Dekker, Inc. x Acknowledgments contributed to the numerical results in Sec 65 DJ Violette wrote the MODIFIED IMAGES program in App B 11 and obtained the numerical results in App A 8 L Giandomenico performed the computer runs that produced the numerical results in Sec 11 1 2 E Vlashi produced the computer plots in App A 6 S Zamoscianyk performed the computer runs and produced the computer plots in App A 7 JL Pearlman performed the MITRE code extensions of the NEC-3 NEC GS and NEC-31 programs discussed in Sec 111 JDR Kramer contributed Eq (D 3) in Appendix D GA Robertshaw, contributed to the discussion in Sec 9 2 1 RL Lagace contributed to the discussion in Sec 1113 and obtained extensive NEC 31 numerical results for electrically short elements and radial wire ground planes with a feed cable, including Table 42 in Sec 13 3 RI Millar WJ Wilson D Lamensdoff, and LJ Tieg reviewed the original manuscripts O Gray J Kalkert, SA Lamoureux, MP Lonergan M Massmger and EA Trottier typed most of the original manuscripts LC Nocca produced the photos in Figs 54 and 57 In Part I I am grateful to A Leitner of Rensselaer Polytechnic Institute for helpful conversations regarding his method of oblate spheroidal wave functions, JH Richmond (deceased) of Ohio State Lmiversity for htlpful conversations and magnetic tapes of his RICHMOND!, RICHMOND2 RICHMOND5, and RICHMOND6 method of moments programs K Awadalla of Menoufia University (Egypt) for helpful correspondence, including a listing of his program for the method-of-moments combined with the geometric theory of diffraction, GH Hufford, ME Johnson and WA Kissick of the Institute for Telecommunica- tion Sciences (ITS) for software of the Longley-Rice and Johnson-Gierhart troposphenc propagation programs and GJ Burke of Lawrence Lnermore National Laboratory (LLNL) for the NEC numerical results of Chapter 5 After I had obtained results by using the integral equation method and the method of oblate spheroidal functions it was possible to confirm the correctness of Richmond s method-of moment results, which were subsequently published (Ref 2) In Part II, I am grateful to RP Rafuse of MIT s Lincoln Laboratory for helpful discussions on antenna structure fabrication remifications in Sec 8 3, RWP King of Harvard University for the Sommerteld numerical results in Figs 76 and 77 in Sec 923 GJ Burke of LLNL for NEC 3 numerical results (in Figs 75-77 of Sec 922 Table 19 of Sec 923 and Table 29 of Sec 1222) Mathematica numerical results (in Figs 80-85 of Sec 933) and helpful discussion concerning the surface wave and the use of the NEC 3 and NEC GS programs GH Hagn of SRI International for Figs 66-69 and contributing to the feed cable discussion in Sec 1113 JH Richmond (deceased) of Ohio State University for contributing his RICHMOND3 and RICHMOND4 method-of- moments programs and WAIT-SURTEES Program, JR wait (deceased) of the University of Arizona for preparing MITRE Report M90 79 Copyright © 2003 Marcel Dekker, Inc.