Compact Bandpass Filter With Multiple Coupling Paths in Limited Space for Ku-Band Application

A compact bandpass filter (BPF) for Ku-band application is proposed in this letter. The proposed filter is composed of five quarter-wavelength (gimel/4) stepped-impedance resonators, which are in staggered arrangement. Folded narrow feedlines are used to introduce multiple coupling paths in limited space. Two symmetrical cascaded quadruplet like (CQ-like) structures are formed and devoted to generate two transmission zeros (TZs) located in both the upper and lower sides of the center frequency (f(0)). Two other TZs are generated by the coupling path between folded narrow feedlines. Two TZs in upper rejection band can be adjusted to special locations to strength the suppression in these points. A prototype of the proposed filter was fabricated and good agreement between simulation and measurement is achieved. The proposed BPF owns the advantages of high selectivity, compact size, low insertion loss, and low cost.