Dual-Polarized Multimode Hemispherical Beam-Scanning and Null-Steering Antenna

A multi-mode antenna capable of hemispherical beam-scanning and null-steering with flexible polarization control is presented. Initially, a compact 18-port antenna operating at a center frequency of 2.45 GHz is designed, utilizing pattern and polarization diversity, achieving isolation of greater than 17 dB between any two ports. The proposed multi-port antenna, which includes a dual-stacked patch structure and a combination of dipoles and monopoles, provides an overlapped operational bandwidth of 2.28–2.64 GHz (14.63%) with an overall dimension of (0.94 × 0.94 × 0.94)λ3Lwhere λLis the free-space wavelength at the lowest operating frequency. Subsequently, the radiation patterns of the individual elements are superposed through an optimization algorithm to create a steerable multi-port antenna with the potential to scan its beam over the entire upper hemisphere. The simulation results show a scanning range of the zenith angle from 0° to 120° and the azimuth angle from 0° to 360° with a gain exceeding 7.5 dBi for all directions in any predefined polarization. Moreover, the versatility of the design and optimization procedure is further demonstrated with additional functions of arbitrary beam-scanning combined with independent control of one-null and dual-null-steering. As a proof of concept, a prototype, excited using a power divider with excitation coefficients derived from the optimization algorithm, is fabricated and tested, demonstrating satisfactory agreement with the simulations.