Design Of The Integrated Substrate Gap Waveguide Based Couplers

With the development of the Internet of Everything and the increase of intelligent mobile terminals,the 4G communication systems have been unable to meet the demand.It is expected that by 2020,it will be the era of 5G.The directional coupler is an indispensable device for isolating,merging,and measuring signals in a communication system.Therefore,it is desired to design a coupling device that can be used for a 5G communication system.Based on three kinds of substrate integrated gap waveguide structures,three couplers are designed based on the branch line coupler,as follows:(1)A wideband 3-dB coupler using substrate integrated gap waveguide(ISGW)is proposed based on the principle of the branch-line coupler structure.The ISGW coupler design is comprehensively studied.It is found that ISGW conducting ridge vias play a significant role and have a strong impact on the cavity resonance,passband and impedance matching.A prototype of the proposed ISGW coupler is fabricated and tested,and the measured agrees well with the simulated.The coupler,better than the reported,has a passband of-5 GHz from 23.59 to 29 GHz with the isolation above 20 dB,covering the 24.25 GH-27.5 GHz and 27.5 GHz-28.5 GHz frequency bands of 5G.(2)A coupler based on packaged substrate integrated gap waveguide structure with star patch is designed.Firstly,the packaged substrate integrated gap waveguide structure is used to package the microstrip branch line coupler.It is found that the obtained package ISGW coupler has 3-dB power division function in the frequency range of 20-26.5 GHz,and 20-dB isolation is achieved in the frequency band of 23-26.5 GHz only.Also,the matching and isolation in the 20-23 GHz band are not good enough.Therefore,to improve the above isolation and matching,four symmetric star patches loaded on the limbs of the coupler are proposed.Thus,the isolation of 20 dB is achieved in the 20-26.5GHz band、and its return loss also reaches-20 dB in the whole frequency band.Moreover,the total additional loss of the packaged ISGW coupler loaded with star patch is 1 dB,which is lower than the loss of single-ridge ISGW coupler.And the packaged ISGW coupler structure with star patch is fabricated and measured.(3)A coupler based on a double-ridge substrate integrated gap waveguide structure is designed.First,the double-ridged PRGW structure is modified to a double-ridge ISGW structure,and then the branch line coupler is designed in the form of a transmission ridge.The coupler based on the double-ridge ISGW structure leads to isolation of 20 dB above in 30-37.5 GHz,and also the isolation of 28 dB and beyond is achieved in the 30.5-35.5 GHz frequency band.The total additional loss is only about 0.7 dB.Therefore,compared with the single-ridge ISGW coupler structure,the double ridge ISGW coupler structure is better for above 30 GHz band,and higher isolation and lower loss are achieved.