Design Of Dual-band Filter And Diplexer Based On Microstrip Gap Waveguide

Gap waveguide is a novel transmission line for microwave and millimeter wave applications.Gap waveguide uses the EBG（Electromagnetic Band Gap）formed by parallel PEC（Perfect Electric conductor）and AMC（Artificial Magnetic Conductor）plate as electromagnetic shielding structure.Compared with traditional metallic waveguide,gap waveguide doesn’t need direct physical contact,so it has higher processing convenience.Microstrip gap waveguide can be realized by planar PCB technology,which has better circuit design flexibility than gap waveguide,and has the advantages of easy integration,miniaturization,and easy fabrication.In the early stage,the wireless communication system only needed to process a single frequency band signal.However,in recent years,the rapid development of wireless communication in the direction of multi-protocol and multi-band makes the wireless communication system more and more demanding on the multi-band function of microwave devices.As an important microwave device in RF front end,the design of filter and diplexer not only meet the requirements of miniaturization,easy integration,easy fabrication and low loss,but also has an urgent need for multi-band function.Therefore,it is of great significance to study and design dual-band microstrip gap waveguide filters and diplexers in this paper.Based on the microstrip gap waveguide,the following work is carried out in this paper:Firstly,a microstrip gap waveguide is designed in this paper.Based on the mushroom-type EBG structure,a microstrip gap waveguide transmission line is realized,and its simulated S₁₁ is better than-20dB over 10.67-19.74 GHz.The microstrip gap waveguide is based on two substrate.The top layer of the upper substrate is the PEC of the microstrip gap waveguide.A transition structure is printed on the bottom layer of the upper substrate,and the upper substrate replaces the air gap.Microstrip ridge and mushroom-type AMC patch is printed on the top layer of the lower substrate.In this paper,the microstrip gap waveguide is fabricated,and measured.Secondly,a dual-mode microstrip gap waveguide resonator and a series of dual-band microstrip gap waveguide bandpass filters are proposed for the first time in this paper.A dual-mode resonator is designed for the first time in microstrip gap waveguide by a series of metalized via-holes into the microstrip gap waveguide to form a cavity resonator,and introducing a microstrip patch to form an open-circuit transmission line resonator.The two modes of the proposed microstrip gap waveguide dual-mode resonator are highly independent,therefore,the resonant frequency of the two modes can be tuned independently.Based on the dual-mode microstrip gap waveguide resonator,a series of microstrip gap waveguide dual-band band-pass filter with different orders are designed,fabricated,and measured.The measured pass bands(S₁₁≤-10dB)are 13.52-13.86GHz and 18.9-19.34GHz with fractional bandwidth of 2.3%and 2.2%while the insertion losses are better than 2.5 dB and 2.3 dB for the third-order bandpass filter.Thirdly,a dual-band microstrip gap waveguide diplexer are proposed in this paper.Based on the dual-mode microstrip gap waveguide resonator,a second-order dual-band microstrip gap waveguide diplexer is realized by designing a good T-type matching network and the a suitable coupling feed network for the two filter elements.The four passbands of the dual-band microstrip gap waveguide diplexer are well matched,and the diplexer has a high degree of isolation.