A Wideband Circularly Polarized Connected Parallel Slot Array in the Presence of a Backing Reflector

This paper presents a wideband circularly polarized (CP) connected parallel slot array that basing on the Wheeler's infinite current sheet concept. The proposed wideband CP array composes orthogonally arranged equivalent magnetic currents with approximately 90° phase difference. Connected parallel slot structure is adopted here to obtain low active input impedance of the array unit cell and realizes good impedance matching without using any extra balun. Shorted microstrip lines and curved phase shift line are used as the feeding. Furthermore, to avoid the backing radiation and keep unidirectional radiation, a metal reflector is added below the array aperture. Then, the connected slot shapes were modified to expand both the impedance and axial ratio (AR) bandwidth. From simulation, the infinite array achieves approximately 3.18:1 impedance bandwidth (from 1.57 to 5 GHz) with active VSWR 3 and 2.4:1 AR bandwidth (from 1.64 to 3.93 GHz) with AR 3 dB. A 4 × 4 CP connected parallel slot array was designed, fabricated and measured to verify the design concept. The measured results reveal a wideband CP performance and unidirectional radiation. Benefiting from the utilization of the backing reflector, the front-back-ratio of the 4 × 4 array is larger than 15 dB and the realized gain approaches the ideal aperture directivity.