Wideband Slot-Coupled Butler Matrix

We present a multilayer 4 × 4 Butler matrix based on corrugated slot-coupled structures, which operates over the complete UWB band (3.1 to 10.6 GHz) with excellent phase and amplitude performance. A prototype has been fabricated which covers the UWB band with a measured return loss better than 21 dB, an isolation better than 24 dB, an amplitude imbalance lower than 1.2 dB and a maximum differential phase error of ±4.5°.