Microstrip-to-Microstrip Vertical Transition With Quasi-Elliptic-Type Dual-Band Filtering Response

A type of two-layer microstrip-to-microstrip (MS-to-MS) vertical transition with quasi-elliptic-type dual-band filtering response is reported. It consists of a MS-to-MS vertical transition on a novel stepped-impedance slotline. To alleviate the radiation losses of the constituent high-impedance slotline sections, two pairs of identical folded low-impedance slotline sections are shunt connected at two ends of the proposed slotline, respectively. By setting the used multiple slotline sections with the specified electrical lengths and impedances, a sharp-rejection third-order dual-band bandpass filter (BPF) response with seven out-of-band transmission zeros (TZs) is attained. The RF operating principle of the conceived vertical transition is discussed by its transmissionline (TL) equivalent circuit. For practical-validation purposes, a proof-of-concept prototype of the devised dual-band MS-to-MS vertical transition is designed, manufactured, and tested. The measured dual-band transition features two sharp-rejection lower and upper passbands with center frequencies of 7.563 and 12.465 GHz, 3-dB fractional bandwidths of 16.86% and 9.7%, minimum in-band power insertion-loss levels of 1.177 dB and 2.104 dB, respectively, and stopband power-attenuation levels above 20 dB from 4.525 to 15.01 GHz (i.e., without considering the passbands).