Design of Dual-Polarized Tilted-Beam Parasitic Array Antenna With Both High Isolation and High Polarization Purity

Design method of accomplishing both high isolation and high cross-polarization discrimination (XPD) of a ±45° dual-polarized parasitic array is presented in this article. To obtain dual polarization under a compact size and single-layer configuration, instead of utilizing two stacked perpendicular radiators, a dual-mode annular ring resonator (ARR) which is capable of maintaining good isolation performance under multiport operation, as is commonly utilized in a hybrid ring coupler, is adopted as the basic element of the parasitic array. Different from antenna arrays whose respective element is directly fed by a specially designed feed network, dual-polarized parasitic arrays face the difficulty of achieving high XPD due to the complex intercoupling among dual polarizations and adjacent parasitic elements. To cope with this issue, an approach for polarization purity improvement of parasitic array is proposed based on thoughtfully investigating the coupling topology of the parasitic array. Moreover, mutual coupling effect is beneficial to dramatically expand the impedance bandwidth of parasitic array compared with the single element, but at the same time, deteriorated isolation performance among two ports needs to be addressed. To this end, a novel feeding scheme is proposed to further enhance the isolation performance of the developed parasitic array. Ultimately, the developed dual-polarized parasitic array exhibits a broad bandwidth of 11.6%, high isolation level of 49.7 dB, and good XPD up to 30.1 dB at a predefined tilt angle of 45°. Besides, the antenna also has a single-layer configuration, simple structure, compact size, and high efficiency.