A Butler Matrix-Based Antenna Array With Improved Gain Flatness and Sidelobe Levels by Using Pattern-Reconfigurable Subarrays

A pattern-reconfigurable subarray is proposed in this letter for the performance enhancement of Butler matrix (BM)-based antenna arrays. The reconfiguration is conducted at subarray-levels and therefore, requires much fewer lumped components than conventional methods. In the proposed design, the pattern of the subarray is switched to different modes for different scanning regions of the overall array, leading to an improvement of gain flatness and sidelobe levels. The reconfiguration is achieved by a novel reconfigurable coupler. By electronically controlling vias connected to a ground plane which severs as binary switches through PIN diodes, the proposed coupler is characterized by extremely low loss even with the capability of reconfiguration. For validation, a
Ku
-band prototype consisting of a 4 × 4 BM and four reconfigurable subarrays is designed, fabricated and measured. Measured results indicate that, the achieved gain fluctuation is only about 0.2 dB between the four scanning beams. The SLL is smaller than −12.1 dB while the gain is larger than 13.8 dB in the scanning plane, which are improved by 5.8 and 1.9 dB than its conventional counterparts, respectively.