Wideband 4 x 4 Butler Matrix in the Printed Ridge Gap Waveguide Technology for Millimeter-Wave Applications

A wideband printed ridge gap waveguide 4 x 4 Butler matrix at 30 GHz is presented. The printed ridge gap technology is used as it has very low losses and supports the propagation of quasi-TEM mode. Each component of the Butler matrix has been designed and analyzed where a superior performance is achieved in terms of bandwidth and size. The designed components are combined to form the Butler matrix. The Butler matrix has a wideband performance where the return loss and isolation levels are higher than 10 dB in the frequency range from 26.9 to 33.3 GHz, the output amplitude imbalance is +/- 1.6 dB, and the phase error is +/- 10 degrees. The measured radiation patterns are in a good agreement with the simulated ones, beam directions are at +/- 13 degrees and +/- 36 degrees at the center frequency. The gain is ranging from 10.2 to 11.35 dBi for excitation from port 1 and ranging from 8.4 to 10.2 dBi for excitation from port 2.