A Circular Patch Fed by a Switch Line Balun With Printed L-Probes for Broadband CP Performance

A broadband circularly polarized (CP) patch antenna fed by a planar balun with a pair of printed probes is presented in this letter. Using switch line structure to design the balun, combined with two printed L-probes to supply dual feed with 90$^{\circ}$ phase difference to the circular patch, the antenna achieves good performance in terms of large impedance and axial ratio (AR) bandwidths. The measured results agree well with the simulations, indicating that the antenna possesses an impedance ( ${\rm S}_{11}< -10$ dB) bandwidth of 45%, and axial ratio (${\rm AR} < 3~$dB) bandwidth of 41%. In addition, the 3-dB gain bandwidth and the peak gain are 44%, and 6 dBi, respectively.