Wideband Circularly Polarized 2 × 2 Antenna Array With Multibeam Steerable Capability

A circularly polarized (CP) switched-beam antenna array with the capability of generating nine steerable beams in the hemispherical space is presented in this letter. A single radiator is first constructed with two triangular-shaped dipoles crossing through printed rings, and four parasitic elements are introduced to enhance the CP operation bandwidth. For the beam steering operation, its array antennas are implemented in a 2 × 2 arrangement and fed by a four-input port feeding network composed of four double-box branch-line couplers. With a suitable feed excitation mechanism, the proposed antenna can generate CP axial beams in nine directions. The antenna is fabricated with an overall size of 2λ
_o
× 2λ
_o
× 0.2λ
_o
(at 6 GHz), and the measured results demonstrate that the proposed design provided very wide -10-dB impedance and 3-dB axial-ratio bandwidths of 48.6% and 46.2%, respectively. Additionally, stable radiation patterns with a gain of approximately 11.5 dBic and radiation efficiency of greater than 90% were observed for every beam direction.