Compact broadband circularly polarized U-slot microstrip antenna

A compact broadband circularly polarized (CP) U-slot microstrip antenna (USMA) with a dual-feed is proposed. By introducing an additional feeding probe near the vertical slot in the conventional singly-fed square USMA on the high permittivity substrate, two series resonances in close proximity are excited. With a non-quadrature phase difference between two feeding ports, broadband circularly polarized can be obtained. The main parametric of the antenna are studied to investigate the effects of primary geometric sizes on the antenna´s performance. A prototype at L-band is fabricated and measured, and the overlapped 14dB return loss (RL) and 3dB axial ratio (AR) bandwidth is over 20% with small overall antenna sizes of 0.33λ0×0.33λ0×0.07λ0