A high-temperature superconducting Butler matrix

This paper presents a novel configuration of a beamforming 16-port Butler matrix centered on a frequency of 2 GHz. The structure is implemented using high-temperature superconductors (HTS). In communication and remote sensing systems, multibeam antenna systems are gradually replacing single-beam systems. Microwave beamformer circuits for these applications require a large number of couplers and phase shifters, which result in a large circuit size. By using microstrip structures on high permittivity substrates, the circuits can be miniaturized. However, the insertion loss of the beamformer increases due to the conductor loss. The use of HTS allows reduction in the size of the circuit while maintaining low insertion loss, due to the low conductor loss compared to conventional conductors. The Butler matrix described here uses a two-layer configuration, which removes any microstrip line crossovers; it can be constructed by traditional photolithographic methods. In this paper, the design of the matrix is discussed, together with the experimental and simulated results.