다층 마이크로스트립 기술에 기반한 광대역 버틀러 4⨉4 빔 성형 네트워크 구현

Abstract

The Butler matrix, which is a feeding system of the beamforming networks, is capable of adjusting the beam direction of array antenna. The beam pattern of array antenna is determined by the magnitude and phase of feeding signal, and interval between antenna elements. Therefore, the magnitude and phase of feeding signal supplied to Butler matrix is used for adjusting the beamforming direction. Since the feeding signal decides on the performance of Bulter matrix, designing each component such as the directional coupler, phase shifter and crossover is very important. In this paper, we propose design methodology for the 4⨉4 Butler matrix to reduce its overall size and improve the performance. The techniques combining three-branch line directional couplers with slot-coupled directional couplers are introduced to extend the limited narrow bandwidth. Especially, in order to minimize the size of beamforming network, the Butler matrix circuit is constructed in a multilayer technology and designed without using a crossover which is one of the essential matrix components. The structural problems caused by multilayer composition are resolved by using the slot-coupled directional coupler. Finally, the Butler matrix was designed and fabricated on double layer microstrip transmission line by the proposed configuration. And also, the simulation results and the measured results were compared for performance analysis each other. As a result, the proposed matrix has good performance that the relative bandwidth, maximum return loss, insertion loss and progressive phase shift are 24 %, 15.76 dB, 6.5 ± 0.8 dB and 9.5 ° in operating frequency band, respectively. Also, the beam pattern according to each input has good coverage with a half power beamwidth of 30 ° within a range of 120 ° sector for mobile base station.