Microstrip antennas

This thesis describes two major research topics: (i) the design of an UWB LHCP low-profile microstrip antenna of Archimedean spiral version; (ii) Modification of the SAC of the Florida Atlantic University's EMI R&D Laboratory to a FAC to perform the required antenna characterizations for the designed UWB antenna. The microstrip spiral antenna is designed to operate in a traveling wave mode. It is constructed on a typical FR4 substrate and is center-fed through an SMA surface-mount connector. An RF chip-resistor located at the outer edge provides impedance matching. The UWB frequency performance of this antenna is among the widest reported in the microstrip antenna literature. The second study refers to a methodology to modify the EMC listed SAC to emulate a FAC. Several pyramidal RF absorbing cones are strategically placed on the reflecting ground surface. The validation between the frequency range 300 MHz to 1 GHz is investigated.

This dissertation is concerned with the studies on the frequency-dependent characteristics of microstrip line structures. Relevant considerations are applied to evaluate crosstalk in symmetric, coupled and lossy (dispersive) microstrip transmission lines. The technique adopted supplements the wide-range of semi-empirical expressions available in the literature on the frequency-dependent even- and odd-mode effective dielectric constants as well as the characteristic impedances of coupled microstrip lines. The accuracy of a crosstalk transfer function deduced is verified with theoretical and experimental results. The behavior of crosstalk versus line-spacing, dielectric substrate characteristics, and line-length is analyzed. This study is also extended to address the influence of temperature on crosstalk induced in microstrip lines. Further, analogous to relaxation considerations of Cole-Cole diagrams as applied to dielectric materials, a "reactive relaxation" concept is introduced to represent the frequency-dependent characteristics of lossless and lossy microstrips. The present algorithm depicting the dynamic permittivity of the microstrip structure (via Cole-Cole diagram) directly leads to a convenient and modified Smith chart representation. It includes the frequency-dependent influence of the fringing field and the lossy characteristics cohesively. Results based on the proposed model are compared with the available data in the literature in respect of a microstrip patch antenna. As far as the authors know of, this is the first attempt in depicting the dispersion characteristics of a microstrip line via Cole-Cole diagram format.