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A new compact microstrip quad‐channel diplexer using quad‐mode square ring resonators (QMSRRs) is proposed. The quad‐channel diplexer is composed of two QMSRRs. A structure consists of two QMSRRs together with one common input and two output coupling lines is proposed, which can remove the matching network and therefore reduce the absolute size of the diplexer. The proposed QMSRR has two transmission zeros at the frequencies between the four resonant frequencies, which can be controlled by changing the length and impedance ratio of the QMSRR. Simulation and measurement results show that the resultant diplexer is of a small circuit size and a high isolation. [ABSTRACT FROM AUTHOR]

In this paper, a dual-wideband bandpass filter (BPF) with independently controllable center frequencies (CFs) and wide stopband suppression is presented using a new quintuple-mode resonator (QMR). By applying the classical odd-/even-mode analysis method, the resonant characteristics of the new QMR have been analyzed. It shows that five modes can be excited, and two of them can be employed to form the lower passband, while the other three modes contribute to the higher passband. For verification, a dual-wideband BPF using the new QMR is designed, fabricated, and tested. Experimental results show that the CFs of the dual-wideband BPF centered at 2.96 GHz and 5.695 GHz with 3 dB fractional bandwidths of 27.7 and 23.4%, respectively. In addition, 20-dB suppression in upper-stopband ranges from 2.23 to 4.04f0, where f0 is the center frequency of the first passband. The measurement results are in good agreement with the prediction results. [ABSTRACT FROM AUTHOR]

A switchable single-wideband ( SWB)-to-dual-wideband ( DWB) bandpass filter ( BPF), which is realized by using lumped switches, is presented in this paper. By alternating the operation modes- ON and OFF-in which the ON mode is achieved by placing the capacitors at the switching spots and the OFF mode is achieved by replacing the capacitors with inductors, DWB-to- SWB BPF can be achieved on the same device. In addition, by changing the capacitor values, the center frequency ( CF) of the lower passband of DWB BPF can be easily tuned from 1.69 GHz to 2.22 GHz, while the higher passband stays almost unchanged. As an example, an SWB-to- DWB BPF is designed, fabricated, and measured. This BPF exhibits good performance including wideband, high isolation, compact size, and ability to switch. [ABSTRACT FROM AUTHOR]