A COMPACT STACKED CIRCULARLY POLARIZED ANNULAR-RING MICROSTRIP ANTENNA FOR GPS APPLICATIONS

A novel design of circularly polarized (CP) annular-ring microstrip antenna (ARMSA) working in TM11 mode is presented. The CP radiations of the proposed antenna are implemented by a 90 branch-line hybrid coupler placed at the inner part of the ARMSA. Since the ARMSA has narrow bandwidth and high-input impedance, a circular parasitic patch suspended above the ring is employed for not only improving the impedance matching and bandwidth, but enhancing the performances of axial ratio (AR). Due to the utilizing of parasitic patch and circular hybrid, the measured results are shown to attain a 10-dB return loss bandwidth of 31.2% (1300-1780 MHz) and a 3-dB AR bandwidth of 19.2% (1360-1650 MHz) respectively. The CP gain is 8.2 dB at 1.575 GHz. The proposed antenna is low profile and has a simple structure, therefore, it can be a good candidate for GPS portable terminal applications.