Miniature quad-band bandpass filter with passband individually controllable using folded SIR

A novel quad-band bandpass filter with individually controllable centre frequencies and bandwidths using a folded stepped-impedance resonator (SIR) is proposed. The new filter that centres at 2.4, 3.3, 4.1 and 5.2 GHz has a measured passband insertion loss of no more than 1.6 dB, and has a miniature circuit size of 0.448λ_g × 0.027λ_g. The presented filter is fabricated and tested, and the experiment demonstrates the new design. The new quad-band bandpass filter has compact and simple circuit topology, good performance of low passband insertion loss and transmission zeros, and greatly reduced circuit size compared with the relative reports.