Dual-Band Linearly and Circularly Polarized Unidirectional Hybrid Loop/Magnetoelectric Dipole Antenna With Single Feeding

Abstract

A dual-band linearly polarized (LP) and circularly polarized (CP) unidirectional hybrid antenna is proposed in this article. The antenna consists of a cross slot antenna (CSA), a pair of vertical and horizontal metal plates, two side walls, and a cavity reflector, fed by a simple single feeding structure. In the lower frequency band, a loop antenna operating in 1λ mode is formed by the ground of the CSA, a pair of horizontal plates, and two side walls, to generate the LP radiation. In the higher frequency band, the cross slot works as a magnetic dipole (M-dipole), while the horizontal plates work as an electric dipole (E-dipole). With the appropriate combination, the magnetoelectric (ME) dipole produces an inherent 90° phase difference for the two orthogonal E-fields to achieve CP radiation. The 1λ modes of the M- and E-dipoles are excited to realize the wideband CP bandwidth. Simulation and measurement are used to study and design the hybrid antenna. The results show that the proposed antenna has an impedance bandwidth (IMBW) of 2.38-2.50 GHz (0.12 GHz, 4.9%) for the LP radiation, and an IMBW of 4.63-7.37 GHz (2.74 GHz, 45.7%) and 3 dB axial ratio bandwidth (ARBW) of 4.10-6.60 GHz (2.5 GHz, 46.7%) for the CP radiation. The radiation patterns at dual bands are stable toward the broadside, having peak gains of 5.75 dBi and 7.53 dBic within the low and high frequency bands.