Abstract
Beamforming networks such as Butler Matrices are important for multibeam array antenna applications. The challenge for Butler Matrix design is that their complexity increases with the number of ports. In this paper, a novel approach of designing a $16\times 16$ Butler Matrix with significant structure simplification is presented. The eight-port hybrids with no crossovers are used to simplify the network. To ensure the network has the same magnitude and phase responses as the standard one, the location and phase shifting value of each fixed phase shifter are derived from the $S$ -matrix of each hybrid. A $16\times 16$ Butler Matrix network operating from 9 GHz–11 GHz is designed to validate this concept. The compensated microstrip 3-dB/90° directional coupler, the phase shifter with a shunt open-and-short stub and the crossover with a resonating patch are used to reduce the transmission loss and enable broadband operation.
Highlights
In recent years, Butler Matrices have been widely used in microwave and millimeter-wave applications such as tracking [1], QAM multiport modulators [2] and multi-port amplifiers [3], etc
Recent studies show that Butler Matrices can be used to generate waves carrying orbital angular momentum (OAM) [9], [10]
Fig. 2 shows the topology of the eight-port network, which consists of four 3-dB/90◦ directional couplers and two fixed phase shifters. #1–#4 are the feeding ports and #5–#8 are output ports
Summary
Butler Matrices have been widely used in microwave and millimeter-wave applications such as tracking [1], QAM multiport modulators [2] and multi-port amplifiers [3], etc. INDEX TERMS Butler matrix, directional coupler, eight-port hybrid, multibeam, phase shifter.
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