Pattern-Reconfigurable Array Based on a Circularly Polarized Antenna With Broadband Operation and High Front-to-Back Ratio

A design for single-fed circularly polarized (CP) antennas with broadband operation and high front-to-back ratio is first described. The antenna is mainly composed of a monopole slot, a dipole, and a metallic box. When the monopole slot is operated in its half-wavelength mode, the radiated fields of the slot and dipole have the same amplitudes and 90° phase differences; in addition, the two radiating elements are arranged in an orthogonal configuration. Consequently, a CP radiation is obtained. Then, the CP antenna is adopted as a radiating element of a 3-D array, and a feed network composed of power dividers is used to excite the array. Both the simulated and measured results prove that the CP array can give a nearly omnidirectional pattern, bidirectional patterns with 8 dBi directivity, and scanned beams with a directivity of 11 dBi. Moreover, the half-power beamwidth of the scanned beam can be changed among 48°, 124°, and 240°. The total size of the array is about 1.5λ0× 1.5λ0× 2.5λ0. Details of the designs for the CP element and array are presented.