A Novel Method From Bandpass to Dual-Band for Microwave Filter and Diplexer Design

Abstract

Abstract-A novel method for a dual-band filter and quad-channel diplexer design is presented in this paper. This method, by altering the gap between resonators, realizes a transformation from bandpass to dual-band for the filter and diplexer. At first, a high selectivity bandpass filter (BPF) with four controllable transmission zeros (TZs) is designed. Then altering the gap between resonators, a band gap is generated and utilized to split the passband of the proposed BPF into two bands, which transform the BPF to a dual-band filter with a narrow passband separation. The center frequency and bandwidth of the new dual-band filter are controllable by adjusting the frequency and width of the band gap. Based on the dual-band filter, a quad-channel diplexer with stepped impedance T-junction is designed, and it can be transformed to a wideband diplexer. For demonstration, the dual-band filter and quad-channel diplexer are fabricated and measured.

Compact diplexer using microstrip half‐ and quarter‐wavelength resonators

“…Generally, the diplexer is implemented by two bandpass filters with common input port and different centre frequencies. The conventional diplexers, just like ones in [1][2][3][4][5][6][7][8], utilise the T-junction to connect two bandpass filters. Just as illustrated in [9], the output segments of the T-junction must been properly designed so that each filter behaves like an open circuit with respect to the other filter at the branch point of the T-junction.…”