A tunable bandpass filter using tapped λ/4 resonators loaded with inductive variable capacitor

This paper presents a tunable coplanar waveguide (CPW) bandpass filter (BPF) consisting of tapped λ/4 resonators with a variable capacitor which operates like an inductive element. Firstly, a tapped λ/4 resonator loaded with an inductor is examined experimentally. Secondly, basic characteristics of the whole element of a lead wire, a chip capacitor, a variable capacitor and a resistor is examined experimentally. After that, tapped CPW resonator loaded with the element above is measured and applied to a BPF. The result of the BPF shows that the center frequency can be shifted about 31.