Radial Probe for Waveguide-to-Microstrip Transition at 265–325 GHz With a Reflective Back Wall

Abstract

To address the structural resonances and impedance mismatch commonly observed in waveguide-to-chip transitions, a radial probe-based structure optimized for wideband and low-loss performance in high-frequency systems is proposed. Impedance matching was improved by incorporating a reflective back wall (RBW), which effectively controlled the resonant behavior of a waveguide-to-microstrip transition. In addition, the dimensions of the enclosure of the radial probe were optimized to improve return loss. A waveguide taper was introduced to compensate for dimensional mismatch with a standard rectangular waveguide, thereby ensuring accurate impedance matching. An equivalent circuit model was developed to provide insight into the electromagnetic behavior of the proposed transition. The prototype was fabricated and mounted on a CNC-machined aluminum split block. The experimental results revealed a bandwidth of 265–325 GHz, with a minimum insertion loss of 0.6 dB and a return loss of more than 15 dB. This confirmed the proposed single-ended waveguide-to-microstrip transition, which incorporated the RBW and the optimized enclosure dimensions to achieve wide bandwidth, low insertion loss, and high return loss. The proposed transition offers a practical solution for wideband, low-loss interconnections in high-frequency systems and can be extended to other waveguide-to-chip configurations.