Fully shielded and self-packaged compact quarter-mode substrate integrated coaxial line bandpass filter for X and K-band

In this work, a dual-mode substrate integrated coaxial line (SICL) bandpass filter supporting single-band and dual-band operation for widely spaced passbands located in (Formula presented.) and (Formula presented.) - band is proposed. Firstly, a cavity conceived with shorted half-wavelength SICL line is investigated. For enhanced miniaturization, a new SICL cavity is developed from the short-circuited half-wavelength SICL line which is bisected along the fictitious magnetic wall to derive its half-mode and quarter-mode counterparts. A fully shielded compact dual-mode dual-band filter is realized by coupling two quarter-mode cavities. The proposed SICL based filter realized using standard PCB fabrication process demonstrates ease of design and enhanced flexibility in exciting the higher order mode to attain the second-passband. The experimental results indicate widely spaced passbands with 3-dB bandwidth of 3.18 GHz and 0.27 GHz centered at 9.61 GHz and 19.12 GHz, respectively. The proposed compact SICL based quarter-mode filter occupies only 0.15 (Formula presented.) lateral area.