A Compact Broadband In-Line Microstrip-to-Waveguide Transition Based on Single-Side Defected Ground Method for Millimeter-Wave Application

This letter presents a millimeter-wave (mmWave) compact broadband in-line microstrip-to-waveguide (M2W) transition based on the single-side defected ground (SDG) method. The proposed SDG method achieves in-line M2W transition within a broadband through grooving the ground surface of the microstrip line (MSL) and shorting the end of the MSL. Furthermore, the SDG structure, aligned in the same direction as the MSL, effectively reduces the dimensions of the transition. The proposed structure of the in-line transition consists of a reduced-height waveguide and a probe with shorted terminals fed by an MSL. An in-line M2W transition operating at the Ka-band is analyzed and designed based on the proposed method. To evaluate the performance of the transition, a back-to-back structure is manufactured and measured. The measured results are in good agreement with the simulation results, confirming the effectiveness of the proposed method. The results demonstrate that the proposed transition reflection coefficient is better than −11 dB, and the insertion loss is between 0.26 dB and 0.6 dB over the 25.3 GHz to 41 GHz (47.4%).