Design of wideband 4 × 4 Nolen matrix using m ultistub loaded phase shifters

Abstract

In this article, a wideband microstrip 4 × 4 Nolen matrix using novel phase shifters is proposed. Because of the unequal electrical paths connecting one input to every output, Nolen matrices in standard form usually introduce significant phase dispersion and amplitude instability, limiting the effective bandwidth. A novel phase shifter consisting of multiple open- and short-circuited stubs is designed, whose rate of change of phase with frequency can be conveniently adjusted. This phase shifter can be used to balance the rate of change of phase with frequency of the unequal electrical paths to reduce the phase dispersion and amplitude instability, thus realizing wide bandwidth of the output phase differences and output amplitudes. To verify the proposed concept, a wideband 4 × 4 Nolen matrix operating at 6 GHz is designed and fabricated, showing a bandwidth up to 33% within ±15° phase imbalance and 21.5% within ±1 dB amplitude imbalance.