A Bidirectional Array of the Same Left-Handed Circular Polarization Using a Special Substrate

Abstract

A novel bidirectional circularly polarized array is presented. The type of circular polarization is the same in both axial directions. The array consists of eight dipoles spaced by λ0/4(λ0 is the wavelength in free space), which combines endfire array, crossed dipoles, and substrate loading. For the bidirectional circular polarization of the same rotation, the adjacent elements need to be excited in phase, and the adjacent +45°/ -45° dipoles need to be excited with 180° phase difference. To satisfy the special phase distribution, a substrate with dielectric constant of 6.0 is used, which makes the guided wavelength λg equal to λ0/2. A prototype is developed at 2.5 GHz. With this array, the measured 3-dB axial-ratio (AR) bandwidth is 770 MHz (2.05 ~ 2.82 GHz), and the 10-dB return-loss bandwidth achieved is 580 MHz (2.32 ~ 2.9 GHz). The maximum bidirectional left-handed circular polarization (LHCP) gain is about 7.3 dBic achieved at 2.45 GHz.