A Broadband Coaxial-to-Elliptical Waveguide Transition Using Step-Impedance Probe

In this letter, a broadband coaxial-to-elliptical waveguide (EWG) transition is proposed using the E-plane stepped-impedance probe (SIP). According to the E-field distribution of the dominate TEc11 mode of the EWG, the SIP is arranged along the short axis of the EWG, and then the dominate TEc11 mode of the EWG can be excited well while its first two high-order modes (TEc21 and TEs11) are suppressed. Accordingly, a wideband transition with single-mode operation is achieved. To obtain good matching in the wideband, four-step SIP is optimized. For verification, a back-to-back transition centered at 4.9 GHz is designed and measured. The measured impedance bandwidth with |S-11| < -15 dB is over 58.4%. Within it, the minimum insertion loss is 0.03 dB. Good agreement between the simulated and measured results can be observed.