Pair of grounded L strips loaded broadband circularly polarised square slot antenna with enhanced axial ratio bandwidth

Abstract

Broadband circularly polarised square slot antenna excited by a coplanar waveguide feed with enhanced axial ratio bandwidth (ARBW) is proposed, designed and experimentally studied. Larger than 21% 3 dB ARBW can be attained by using asymmetric feed and implementing a T‐shaped grounded stub from the left side of the square slot in orthogonal direction towards the slot centre. To further enhance the 3 dB ARBW of the proposed slot antenna, a pair of equal grounded L‐shaped strips with different sizes is embedded at the top right corner of the square slot. Small L‐shaped grounded strip plays an important role for merging two closely spaced multi‐resonant modes, generated by the combined effect of asymmetric feed with T‐shaped grounded stub and with large L‐shaped strip. Overall size of the proposed antenna is 40 × 40 × 1.6 mm 3 . Measured value shows that the impedance bandwidth and 3 dB ARBW of the designed antenna are 73.39% (5.02–10.84 GHz) and 58.08% (5.07–9.22 GHz), respectively. Good agreement is achieved between simulated and measured results.