A Ka-Band All-Metal Multibeam Antenna Array Fed by Filtering Butler Matrix

In this paper, a Ka-band all-metal
$1\times 4$
multibeam antenna array utilizing a filtering Butler matrix is proposed. The Butler matrix is comprised of all-resonator 180° filtering hybrids, 90° couplers, and phase shifters, providing incremental phase shifts with a bandpass characteristic. To realize multibeam radiation, four wideband horns are utilized. The novel design eliminates the necessity for crossovers and connectors between the Butler matrix and radiators, resulting in a more compact structure. The simulated results exhibit an impedance bandwidth (return loss > 10 dB) of 28.0-29.9 GHz, delivering a gain of up to 16.6 dBi. It demonstrates stable radiation in multiple beams at 0°, ±23°, and ±46°. Moreover, beyond the operating band, the gain experiences a sharp decline of more than 45 dB/GHz.