SIW Butler Matrix with Modified Hybrid Coupler for Slot Antenna Array

This paper presents a substrate integrated waveguide Butler matrix with a modified hybrid coupler, operating from 28 to 32 GHz. The modified hybrid coupler is realized by using 90 degrees hybrid coupler followed by a -45 degrees compensating phase shifter. Thus, 45 degrees/135 degrees ffi output phase differences can be obtained using this type of coupler. Compared with the equal-length unequal-width phase shifter, the compensating phase shifter exhibits better phase characteristics, with only 3 degrees phase error over 28-32 GHz. Because the phase of compensating phase shifter is not realized by taking the phase introduced by the crossover as a reference, it gives great flexibility to the design of compensating phase shifter. Adopting the modified hybrid coupler, the designed Butler matrix features the output phases with peak to peak error of 13 degrees and wideband performance from 28 to 32 GHz. The slot array fed by the Butler matrix can radiate four slanted beams with acceptable measured gains, in the range of 9.7 similar to 12 dBi for port 1 excitation and 8.4 similar to 11.1 dBi for port 2 excitation. The radiated beams can reach a wide azimuthal coverage between +/- 61 degrees.