Mutual Coupling-Based Compact Wideband Circularly Polarized Antenna

A small-size wideband circularly polarized (CP) antenna is introduced. The key innovation is that the antenna is based on four confined highly coupled microstrip patches fed by a composed right-left-hand integrated feeding network (FN). Mutual coupling is thus effectively used in a constructive way. It is shown that this idea results in an excellent combination of axial ratio (AR) bandwidth and small size. A prototype was built and measured proving the concept in practice. The impedance bandwidth is 110%, the AR bandwidth at broadside is more than 83%, and the −3 dB gain bandwidth (with respect to maximum gain) is 65%, with an overlap of 63% when considering all the three at the same time. The antenna lateral size is as small as
$0.52\lambda 0\times 0.52\lambda 0$
, where
$\lambda 0$
is the midband wavelength.