Dual-frequency circularly polarized annular-ring slot antenna fed by a double-bent microstripline

A novel design of a dual-frequency circularly polarized annular ring slot antenna is presented. The dual-frequency characteristic is achieved using a single-layer double-bent microstripline-fed configuration coupled to a dual-annular ring slot antenna. The 10 dB return loss impedance bandwidths (VSWRles2) for the lower and higher band are 31.3% and 10.6%, respectively. The 3 dB axial-ratio bandwidths are 10.5% and 1.5% with respect to 2.15 GHz and 3.8 GHz, respectively. The proposed antenna with broad axial-ratio bandwidth at the lower frequency and simple structure is easy to be fabricated and adjusted.