A DUAL-BROADBAND CIRCULARLY POLARIZED ANTENNA WITH UNIDIRECTIONAL RADIATION PATTERN

A dual-band circularly polarized (CP) antenna with wide axial ratio (AR) and impedance bandwidths is proposed. Based on a rectangular ground, the antenna consists of a trapezoid patch, an L-shaped strip, a cavity, and T-shaped and L-shaped perturbations. By embedding a feeding line with a trapezoid patch and an L-shaped strip, dual-band input impedance performance and a CP performance at upper band are obtained. In order to achieve a CP performance at the lower band, a T-shaped perturbation is embedded inside the slot. Moreover, the CP performance is enhanced by inserting an L- shaped perturbation at the right bottom corner of the slot. Furthermore, using a cavity underneath the antenna, unidirectional radiation patterns with greatly gain enhancement are obtained. The measured results show that the impedance bandwidths for S11 < i10dB are 22.7% (2.34{2.94GHz) and 79.8% (4.64{10.8GHz) while the axial ratio bandwidths (AR < 3dB) are 26.4% (2.3{3GHz) and 12.6% (5.2{ 5.9GHz) at the lower and upper bands, respectively. Additionally, the measured gain is more than 7.4dB and 2.4dB in the two operating bands, respectively. Thus, the antenna can be well applied for both 2.4/5.8GHz WLAN bands and 2.5/5.5GHz WiMAX bands.