Dual Mode Dual-Band Circularly Polarized Modified Square Ring Antenna

This paper proposes a dual-band circularly polarized (CP) modified square ring antenna. The resonate structure of this antenna consists of a modified square ring patch and a ground plane, and the antenna is fed by a modified L probe with two unequal branches. A low order CP mode (TM11 Mode) and a high order CP mode (TM12 Mode) are both excited in this simple structure for the dual band operation. The truncated corners of the ring and the embedded corners of the slot are used to obtain the dual band CP operation. The overall size of the antenna is 150 × 150 × 11.7 mm3. The measured 10-dB return loss bandwidths are 13.0% for the lower 2.45 GHz band and 37.4% for the upper 5.8 GHz band. The measured 3-dB axial ratio bandwidths are 2.1% and 5.8% for the lower band and upper band respectively. The measured peak gains of the lower band and upper band are 8.19 dBic and 9.44 dBic respectively.