A $Ka$ -Band High-Gain Circularly Polarized Microstrip Antenna Array

In this letter, a four-element high-gain circularly polarized microstrip antenna array operating in the Ka -band is proposed. The sequentially rotated series-parallel stub technique is employed in constructing the feed network to allow symmetrical positioning of microstrip patch elements, resulting in good axial ratio of polarization. In addition, an L-shaped matching branch is used to offer good impedance matching and spatial flexibility for positioning patch elements. Both simulation and measurement results are presented. They agree with each other well and demonstrate much better 3-dB axial-ratio bandwidth and return loss than the single patch antenna.