A tunable dual-stop-band filter using spurlines

A miniaturized tunable dual-stop-band filter featuring compact size and spurious free passband is introduced in this paper. The two stopbands can be tuned independently. The filter consists of a pair of revised spurlines. By embedding two varactors in the transmission line, a tunable dual-band bandstop filter is implemented. One stopband that has 41% tuning range centered at 2.57 GHz with |S₂₁| better than 10dB, and the other stopband that has 13.3 % tuning range centered at 4.65 GHz with |S₂₁| better than 15dB have been obtained. The absolute 3dB bandwidth of first stopband is less than 515MHz, and the second is less than 930MHz. The predicted results are compared with measured data and good agreement is reported, which verifies the proposed method. This kind of filter behaves similarly to the conventional open-circuited shunt-stub band-stop filters, but is more compact and has less radiation and dispersion, and is less susceptible to the influence of adjacent objects.