Compact Triple-Band Active Switchable Bandpass Filter With Enhanced Passband Isolation

In this letter, a compact bandpass filter (BPF) is proposed, which can independently work among S, C, and X bands. The structure of each band is designed separately, and the working frequency can be selected by active switches. To reduce the overall size, the filter uses stacking technology and vertical feedlines to combine each part. Moreover, doubling resonance suppressions are applied in S band by the stepped-impedance resonator to achieve enhanced passband isolation. The designed filter has three passbands at 2.09–3.77 GHz, 3.95–7.25, and 7.78–11.2 GHz, respectively. The simulated results have excellent agreement with the fabricated ones. The proposed work has promising applications in microwave communication scenarios that need higher isolations of working bands.