Design of Microstrip Antenna with Modified Annular-ring Slot for GPS Application

A circularly polarized annular ring slot antenna with broadband impedance and circularly polarized bandwidth characteristics has been presented in this paper. By introducing proper asymmetry in the annular ring slot structure in the form of two pairs of slits, and feeding the ring slot using a 50 Omega microstrip line, the bandwidth is increased, and the circularly polarized antenna is also formed for GPS application. The measured results agree with the simulation, showing that the proposed antenna has a wide return loss and AR bandwidth (AR < 3 dB) of more than 40% referred to the resonant frequency 1.575 GHz. The measured radiation patterns are stable and symmetric with respect to the broadside direction. Moreover, a prototype antenna with an average gain of 3.2 dBi over a CP bandwidth is shown.