Compact 28 GHz Folded Butler Matrix Using Low-Temperature Co-fired Ceramics

Abstract

This paper introduces a miniaturized Butler matrix design method using a folded structure. The Butler matrix was fabricated in multilayers using low-temperature co-fired ceramics (LTCC) and designed to operate at 28 GHz. The conventional one-plane Butler matrix has a major disadvantage in that the length and volume of the system inevitably have to be increased. By using the proposed folded structure, the length can be reduced more than two times compared to the general one-layer Butler matrix. In order to minimize the loss of the Butler matrix, it was designed in a stripline structure by forming a ground plane on the upper and lower surfaces of each layer. A signal is transmitted between the layers through via holes. A 4 × 4 Butler matrix was fabricated and measured for the demonstration of the proposed concept. The proposed Butler matrix was measured through a precisely calibrated antenna chamber with closed cell absorbers. The dimensions of the fabricated Butler matrix are 14 mm × 20 mm × 1.52 mm. The beam of the fabricated Butler matrix can be properly steered in a total of four directions.