This paper presents the design of frequency-tunable dual-band, tri-band and quad-band bandpass filters (BPFs). The proposed three BPFs can be independently tuned and individually switched by varying the capacitances of the varactors. In the designed tunable dual-band BPF (TD-BPF), common input/output feed lines are utilized for two tunable dual-mode resonators (TDRs). Further, three TDRs and four TDRs are employed to achieve tunable tri-band BPF (TT-BPF) and tunable quad-band BPF (TQ-BPF), respectively. Then, the TD-BPF and the TT-BPF are fabricated and measured to verify individual tunability and independent switchability. For the TD-BPF, the measurement results show that the center frequency (CF) of the first passband varies from 1.37 to 1.62 GHz, and the CF of the second passband varies from 2.3 to 2.64 GHz. In the measured TT-BPF, the tuning ranges of CFs of three passbands are 1.3–1.5 GHz, 2.36–2.6 GHz, and 3–3.54 GHz, respectively.

中文翻译：

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具有独立频率可调和可切换通带的紧凑型双/三/四频带带通滤波器

本文介绍了频率可调的双频带、三频带和四频带带通滤波器 (BPF) 的设计。所提出的三个 BPF 可以通过改变变容二极管的电容来独立调谐和单独切换。在设计的可调谐双频 BPF (TD-BPF) 中，公共输入/输出馈线用于两个可调谐双模谐振器 (TDR)。此外，三个 TDR 和四个 TDR 分别用于实现可调谐三频 BPF (TT-BPF) 和可调谐四频 BPF (TQ-BPF)。然后，制作并测量 TD-BPF 和 TT-BPF，以验证单独的可调谐性和独立的可切换性。对于 TD-BPF，测量结果表明，第一通带的中心频率（CF）在 1.37 到 1.62 GHz 之间变化，第二通带的中心频率（CF）在 2.3 到 2.64 GHz 之间变化。在测量的 TT-BPF 中，