A COMPACT CIRCULARLY POLARIZED MICROSTRIP ANTENNA WITH BANDWIDTH ENHANCEMENT

A novel compact circularly polarized microstrip antenna (CPMA) with bandwidth enhancement is proposed and studied. By employing capacitive loading and inductive loading, the size miniaturization is achieved. The cross-shaped aperture in the ground plane is able to excite two orthogonal modes. The near-equal amplitudes and 90 ◦ phase difference between these two modes are realized by properly designing the feed network, i.e., a 0 ◦ -90 ◦ hybrid comprising a 3-dB Wilkinson power divider cascaded with a 90 ◦ phase shifter. The proposed antenna exhibits a global bandwidth of 11.5% ranging from 1.88 GHz to 2.11 GHz with an overall size 50 mm × 50 mm × 6. 8m m (0.33λ0 × 0.33λ0 × 0.045λ0). The global bandwidth is defined where return loss is larger than 10 dB, broadside axial ratio (AR) smaller than 3 dB, and gain above 0 dBic.