Circular Microstrip Antenna Loaded With Shorting Posts and Sectoral Slots For Lower Cross-Polar Radiation

A lower cross polarization level in the radiation pattern of microstrip antenna is needed for achieving the pattern and polarization purity. The main source of cross-polar radiation in microstrip antenna is the residual contribution of higher order resonant modes present at the fundamental resonant mode frequency. In this paper, designs of circular microstrip antenna either loaded with ground plane 900 Sectoral slots or shorting posts placed on the patch or the combination of slots and shorting posts, are proposed for the cross-polar level reduction at the fundamental mode. These techniques increase the spacing of TM21 mode frequency with respect to TM11 mode that achieves reduction in the cross-polar levels. Amongst all the techniques presented, design with five shorting posts yields cross-polar reduction by 48 dB in the broadside direction, whereas combination of shorting posts and 900 Sectoral slots achieves 45 dB cross-polar reduction against the circular patch employing the conventional square ground plane. An experimental validation for the simulated results has been carried out that shows a closer agreement.