Broadband Circularly Polarized Square Slot Antenna with a Novel CPW-FED Structure

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Abstract
A new design of a broadband circularly polarized (CP) square slot antenna is presented. An excellent CP bandwidth can be obtained by using a novel coplanar waveguide (CPW) fed structure, which consists of a widened square tuning stub at the end of an asymmetric inverted-L signal strip and a pair of I-shaped strips along they -axis at two opposite sides of the square tuning stub. Axial ratio (AR) bandwidth can be significantly enhanced by adjusting the length of the pair of I-shaped strips. The antenna has been investigated numerically and experimentally. Experimental results show that the antenna possesses an impedance bandwidth of as large as 50% with voltage standing wave ratio (VSWR) less than 2 and a 3 dB AR bandwidth of 51.7% relative to the centre frequency of 2.2 GHz. The 3 dB gain variations are less than 1 dBi within the CP bandwidth.