LAUSR

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 mm3. 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.