Circularly Polarized Loop Antennas with Balanced, Unbalanced, and Quasi-Balanced Feeds

Three different feeds are used to realize a loop antenna with wideband circular polarization. The loop is backed by the ground plane and analyzed using the moment method. It is found that the antennas with balanced and unbalanced feeds radiate left and right-hand circularly polarized waves with 3 dB axial ratio bandwidths of 13% and 3%, respectively. Subsequently, the balanced feed is transformed into a quasi-balanced one for impedance matching. It is found that the VSWR remains less than 2 in an axial ratio bandwidth of 11%.