Log-periodic array of circular microstrip patches.

Abstract

Presented in this thesis are the results of theoretical and experimental investigations carried out on the radiation characteristics of log-periodic array of electromagnetically coupled circular microstrip patch antennas. Motivated by the inherent drawback of narrow bandwidth of the single microstrip patch antenna, an attempt has been made to enhance the bandwidth by applying the conventional log-periodic arrangement of the microstrip patches. Since for an array of such radiating elements, it is convenient to make use of electromagnetic coupling between the feed line and the array, a detailed study of a single electromagnetically coupled circular patch has been carried out and an appropriate equivalent circuit has been proposed based on measured return-loss and impedance results. Experiments have been done on a large number of single patches to confirm the validity of the proposed equivalent circuit. Using this equivalent circuit, the theoretical analysis of the log-periodic array of electromagnetically coupled circular microstrip patches has been carried out. The expressions for input impedance, radiation pattern and the gain of the array have been derived. Using these expressions, numerical computations have been made for log-periodic array of eight circular microstrip patches designed for a frequency band of 4.5–7.0 GHz. This array has been fabricated on a low dielectric constant microwave substrate. Measurements of the above-mentioned characteristics of the array have been carried out. Theoretical and experimental results have been compared. There is good agreement between the measured and calculated results.