Theoretical and experimental studies on the microstrip-fed inverted patch antenna with linear or circular polarization

A microstrip-fed inverted patch antenna with linear or circular polarization, holding an air layer between the patch and the ground, is proposed to realize the broad-band patch antenna printed over a very thin substrate at the low-cost level. For a linearly polarized type, its input characteristics are rigorously characterized by a novel spectral-domain moment method. Compared with the conventional patch antenna, its bandwidth is found to be sharply improved, numerically from 0.246% to 3.48%, and experimentally from 0.290% to 2.95% for a patch antenna matched by a quarter-wavelength transformer. For a circularly polarized type, its electrical characteristics are efficiently designed by the cavity model approach based on the simulated input resistance of the linearly polarized patch antennas. Its measured axial ratio (AR) is found to be lower than -0.5 dB at the designated resonant frequency (f/sub 0/=2.0 GHz), while its AR bandwidth is measured to be about 1.0%. Moreover, all the measured parameters are found to be in excellent good agreement with the simulations at the frequency shifts less than 2.0% and at the measured return losses less than -15.0 dB.