U-band 3D integrated bandpass filter with four controllable transmission zeros

A three-dimensional integrated substrate integrated waveguide bandpass filter has been demonstrated by using low-temperature co-fired ceramic technology. By adopting the extracted-pole and the cross-coupling mechanisms simultaneously, four controllable finite transmission zeros outside the passband are achieved to realise high selectivity. A U-band prototype has been designed, fabricated and tested. The measured results match well with the predicted theoretical counterparts. The proposed filter has the merits of desirable insertion loss, high design freedom and good out-of-band rejection.