Compact inline dual-mode dielectric waveguide diplexers with controllable transmission zeros

Abstract In this paper, compact inline dielectric waveguide resonator (DWR) diplexers with controllable transmission zeros (TZs) are precisely designed by using novel combined TM 110 mode DWRs and TM 120 /TM 210 dual-mode DWRs. Resonance behaviors of the dual-mode DWR and coupling mechanisms among TM 110 , TM 120 , and TM 210 modes are investigated. Both positive and negative couplings are realized by simply adjusting the position of a coupling blind hole, thus achieving precise control of TZs. Accurate designs of the two diplexers are accomplished with fully controllable bandwidths and TZ positions. Finally, a 3-pole inline diplexer is fabricated and measured with the lower and upper channels operating at 3.35 GHz and 3.55 GHz, respectively. The measured insertion losses of both channels are less than 1.05 dB, while the isolations in both channels are larger than 32 dB. Although the diplexer employs dual-mode DWR and there are no extra tuning screws to fine-tune the resonance frequencies and couplings, the measured response matches very well with the simulated response.