D-band Circulator Based On Substrate Integrated Waveguide

The circulator is an indispensable microwave device in the RF front-end.and the non-reciprocality of the ferrite spin magnetic material allows its signal to be transmitted in one direction.First of all,with the large-scale commercial use of 5G,the research and development of 6G has been put on the agenda,and the terahertz band has been a research hotspot for communication systems in recent years,and the D-band is its research point.Among them,140 GHz,as one of the atmospheric windows,has a narrow beam,small loss,strong anti-electromagnetic interference ability,and high research value.Secondly,the rapid development of the semiconductor industry in recent years has put forward new requirements for microwave devices in wireless communication systems: how to achieve small size,high integration and high performance.Substrate Integrated Waveguide(SIW)is a new type of microwave transmission line that meets the needs of current communication development.Finally,this thesis proposes a140 GHz SIW circulator to meet the development needs of future communications.The work of this thesis is summarized as follows:First,the D-band SIW transmission line is designed.In order to better design the circulator,two D-band coupling structures are proposed,including the Leroy coupling structure based on double-layer SIW and the tesla junction coupling structure based on stripline.The filtering effect of high selectivity of D-band is realized.The overall geometric size of the Lelow coupling structure is 2.2×3×0.56 mm,and the overall design size of the tesla junction coupling structure is 1.6×3×0.25 mm,both of which take into account the advantages of small size and simple structure.Then the design theory of the junction circulator and the characteristics of ferrite spin magnetic materials were discussed,the D-band SIW circulator was designed,and then the matching principle and method of the port impedance were introduced,and the looper port was further matched with the 50? microstrip line impedance,and the overall geometric size of the matched circulator was 1.8×1.8×0.22 mm.The index is its center frequency of 140 GHz,in the range of 139.3 ?140.7GHz frequency,the insertion loss is less than 0.5d B,and the return loss and isolation are greater than 20 d B.Finally,a single-ridge SIW circulator is further designed.By improving the structure,a gap is introduced between the inner side of the ridge and the middle of the ferrite to improve impedance matching,thereby broadening the bandwidth.The final design index is the center frequency of 140 GHz.In the frequency range of137.4?141.6GHz,the return loss and isolation are greater than 20 d B,and the insertion loss is less than 0.4dB.