A Structurally Reused Hybrid Integrated Ridged–Air-Filled Substrate Integrated Waveguide for Large-Frequency-Ratio X–K- and E-Band Cross-Band Operation

This article introduces a new concept for realizing multi-band large-frequency-ratio microwave transmission lines (TLs) tailored for 5G integrated sensing and communication. A new class of wideband hybrid ridged–air-filled substrate integrated waveguide (HR–AFSIW) architecture is proposed. The key idea is structurally reusing an embedded air-filled substrate integrated waveguide (SIW) as the ridge of a ridged SIW, thereby forming two independent propagation channels. These channels operate at two well-isolated frequency bands, each supporting a large TE10-mode bandwidth with significantly different cut-off frequencies, inherently yielding a wide frequency ratio. A proof-of-concept HR–AFSIW prototype operating at X–K- and E-bands is developed with independent output transitions to grounded co-planar waveguide and rectangular waveguide ports, respectively. Experimental validation in a back-to-back configuration confirms the desired dual-band large-frequency-ratio (>5:1) performance of the proposed TL, featuring single-TE10-mode bandwidths spanning 7.6–20 GHz and 63.8–86.4 GHz.