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Fundamental TM11 mode of circular microstrip antennas has a limitation of low broadside gain. This thesis explores and investigates the possibility of designing high gain circular microstrip antennas by using higher zeros of the first order mode, or the TM1m modes. Deficiencies in the existing methods of gain enhancement, motivates the need to look for new methods. This is done by first investigating the radiation characteristics of TM1m modes, and then providing techniques for sidelobe suppression in their radiation patterns. Several approaches are proposed and corresponding to each developed technique, an example of high gain antenna is designed, fabricated and experimentally evaluated. First, through the radiation characteristics of a magnetic loop over an infinite ground plane, we explain the occurrence of high sidelobes in the E-plane radiation patterns of the TM1m modes. By noting the peak directivity and sidelobe variation with loop size, we propose, investigate and demonstrate the use of high permittivity substrates to reduce the sidelobes in the TM12 mode. Second, to remove the dependence of the radiation characteristics on high permittivity substrates, another technique to suppress the high sidelobes of TM12 mode, is presented. It is found that introducing a narrow nonresonant rectangular slot at the patch center, sidelobes of the TM12 mode can be effectively suppressed. Sidelobe level (SLL) suppression is demonstrated by both simulation and measurement, using various configurations. Third, it is proposed that linearly superimposing the radiation fields of either odd or even zeros of the first order mode, can achieve both high gain and low sidelobes. To show this, stacked antenna configurations of TM11 and TM13 modes are thoroughly investigated and SLL suppression is demonstrated. Finally, to leverage further advantage of the linear superposition of modes, a single layer annular slot loaded antenna configuration is proposed. The proposed new configurations are based on higher order TM1m modes, which, for excitation, requires electrically large conducting discs. This property offers one more advantage at high frequencies, where antenna size becomes too small for the fundamental mode to fabricate and feed. The proposed electrically large antennas eliminate these problems, and become more practical to fabricate. / February 2017

International Telemetering Conference Proceedings / October 26-29, 1992 / Town and Country Hotel and Convention Center, San Diego, California / A new antenna design, which is particularly suited for balloon telemetry applications, is presented. In the past, simple monopoles have been utilized as transmit antennas on balloon payloads. The monopole radiation pattern has an inherent null along its axis. This causes an undesirable loss of signal when the balloon is directly overhead. To prevent this occurrence, a microstrip antenna patch was incorporated into the monopole design. This combination, a "monopatch" antenna, provides sufficient coverage even when the balloon is directly over the ground station. The monopatch has been successfully flown on high altitude balloon flights.

Made available in DSpace on 2014-06-12T17:39:43Z (GMT). No. of bitstreams: 2 arquivo6947_1.pdf: 3745314 bytes, checksum: 13254d1210d7522089459fcc07d6e7fa (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2006 / Esta dissertação trata do desenvolvimento de modelos, da análise e realização de linhas de transmissão, acopladores e filtros de linhas acopladas em microstrip, utilizando estruturas comblines para obter reduções da dimensão final desses dispositivos em freqüências de microondas. O trabalho desenvolvido é constituído de três partes. A primeira propõe modificação em um modelo existente de análise e projeto de linhas em microstrip comblines, modificação esta que tem como objetivo melhorar o dimensionamento do projeto inicial da microstrip combline, tornando-o bem mais preciso, reduzindo desta forma os ajustes necessários para realização desse tipo de dispositivo. A segunda parte propõe um modelo de análise e projeto de linhas acopladas que utilizam microstrip comblines com o objetivo de reduzir a região de acoplamento e, dessa forma, reduzir o comprimento do dispositivo. Mostra-se, também, que é possível aplicar esses modelos na redução dos filtros de linhas acopladas em microstrip. A terceira parte trata da confirmação dos modelos obtidos, utilizando softwares de simulação eletromagnética, bem como de medidas nos protótipos construídos. A linha de transmissão, o acoplador e filtro construídos com microstrip comblines mostraram uma redução de aproximadamente 30% em suas dimensões finais, quando comparadas com as dos dispositivos originais

Thesis (Ph.D.)--City University of Hong Kong, 2006. / "Submitted to Department of Electronic Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy" Includes bibliographical references (leaves 179-189)

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