Broadband Substrate Integrated Waveguide 4$\,\times\,$4 Nolen Matrix Based on Coupler Delay Compensation

A broadband Nolen matrix in substrate integrated waveguide (SIW) technology is proposed and studied in this paper. Being serial feeding networks, Nolen matrices usually introduce significant phase dispersion in their standard form, thus limiting effective bandwidth. In this work, broadband frequency operation is achieved with adequate coupler delay compensation, resulting in a more "parallel" matrix topology. Consequently, H-plane couplers with continuous aperture are preferred in the proposed design as opposed to the cross-couplers previously used in the "serial" configuration. The SIW couplers and phase shifters of a balanced amplitude 4×4 Nolen matrix are designed at 77 GHz for radar applications. The resulting matrix that combines these elementary building blocks is fabricated and measured, and measured characteristics are in good agreement with theoretical and simulated predictions. This first design achieves excellent results over a 11.7% frequency bandwidth centered at 77 GHz. This modified Nolen matrix combines advantages of standard Nolen and Butler matrices and may be used as a building block for generalized orthogonal matrices.