Circular Polarized Square Micrsostrip Antenna Using Modified Ground Plane

The use of defected ground plane structure in microstrip antenna is reported for realizing multi-band and wide band characteristics. However, in the literature an in-depth study providing resonant mode based explanation for antenna working is missing. Here in present paper, circularly polarized square microstrip antenna design using vertical slots embedded on ground plane (defected ground plane) is presented. Using supportive resonance and current distribution plots it is shown that ground plane slot alters field distribution present on square patch at fundamental mode. This realizes optimum spacing between orthogonal fundamental patch modes which results in circular polarization. The antenna offers axial ratio bandwidth of 114 MHz (10.6%) that lies inside the impedance bandwidth of 669 MHz (52%). Across the BW, proposed configuration exhibit bore-sight radiation pattern with maximum gain of 5 dBi.