Full-Band Air-Filled Waveguide-to-Substrate Integrated Waveguide (SIW) Direct Transition

A 45% bandwidth in-line air-filled waveguide-to-substrate integrated waveguide (SIW) direct transition is designed to greatly improve the performance of existing configurations. The transition, based on a four-section height-stepped waveguide, includes a single-step widening transformer that enables full-band operation without using any dielectric probe. The absence of the probe reduces significantly the insertion loss and makes this transition simple, bandwidth controllable and easily scalable to the millimeter-wave frequency range. A back-to-back transition is designed to cover the 32–50 GHz band showing a return loss of 15 dB and a mean insertion loss of 0.68 dB in the whole bandwidth.