A Novel 4 × 4 Waveguide Butler Matrix for Multiport Amplifier

This paper presents a novel single-layer $4 \times 4$ Butler matrix using only branch waveguide couplers, which consists of four 3 dB hybrid couplers and a crossover. It achieves simulated return loss better than 25.7 dB, isolation better than 22.7 dB, amplitude imbalance less than 0.56 dB, and phase fluctuation less than ± 7° in the frequency range of $17.7-20.2 \mathrm{GHz}$, which is the transmit band of Ka-band telecommunication satellites. The proposed Butler matrix can be used for multiport amplifiers to achieve flexible power allocation among the output ports of a multibeam system.