Ka-Band Multibeam Patch Antenna Array Fed by Spoof-Surface-Plasmon-Polariton Butler Matrix

A novel Ka-band spoof-surface-plasmon-polaritons (SSPPs) Butler-matrix-fed multibeam patch antenna array is proposed. An SSPPs-fed single-layered microstrip patch antenna with suppressed cross-polarization is investigated acting as the radiator. By using SSPPs etched on both sides of a substrate, a 3 dB coupler, a crossover, two phase shifters, and a vertical interconnection with compact geometries and promising performance are designed and investigated. By connecting the devices together, an SSPPs Butler matrix is realized, whose topology is modified in order to compensate for the phase influence of the SSPPs couplers that are different from traditional results. The
$1\times4$
multibeam patch array fed by the SSPPs Butler matrix is fabricated and measured. An impedance bandwidth of 15.4%, a gain of up to 12 dBi, and stable radiation beams are obtained. Benefitting from the small ratio between the metal area and the overall array area and the promising operating performance, the proposed SSPPs fed multibeam array may find potential applications in millimeter-wave systems where the absence of a large ground is preferred.