Miniaturised highly selective wide-band bandpass filter using dual-mode resonators and inter digital capacitors

A wide-band bandpass filter with high selectivity, compact size and wide stopband is presented in this Letter. This proposed filter uses dual-mode resonators (DMRs) as its basic tool. Stepped impedance technique is adopted in designing the DMRs for miniaturising its size. In the construction of filter design, three types of inter digital capacitors (IDCs) are employed; one is used for coupling between DMRs and other two are used at feed lines. The IDCs and open stub resonators are infused in the filter for curbing the harmonics and providing wide stopband. Input–output cross coupling is introduced by making use of hook-shaped feed lines for achieving good selectivity. A miniaturised size of 0.089λg × 0.10λg (29.2 × 33 mm2) with wide stopband up to 10.1f 0 (f 0 is the operating frequency of filter) with 21.5 dB harmonic suppression level is achieved with this design.