| Millimeter wave features large bandwidth,narrow beam,good security,high Doppler resolution,small device size and easy integration,and has a broad application prospect in5 G mobile communication,Internet of things,radar,satellite communication and other fields.In order to further realize the integrated integration of millimeter-wave communication systems,multilayer millimeter-wave circuit design has become a current research hotspot.The multi-layer circuit structure allows passive and active devices to be integrated in the three-dimensional direction,greatly reducing the size of the system.In the multilayer circuit structure,the signal transmission of devices between different layers is mainly realized through vertical interconnection.As a key part of the slotline coupling transition structure,it directly affects the performance of the whole circuit system.Liquid Crystal Polymer(LCP)is an ideal packaging material for millimeter-wave communication systems because of its high thermal stability,low dielectric loss,wide frequency range,and high strength.In view of the many advantages of LCP millimeter wave packaging substrates,this paper focuses on the research and design of heterogeneous transmission line slot-line coupling transition structures,and the main work is as follows:(1)Due to the narrow bandwidth of the conventional slotline coupling transition structure,this paper innovatively introduces the slotline multimode coupling theory into the design of millimeter-wave slotline coupling transition structure.The paper focuses on the analysis of the resonant modes of the slotline resonators in the microstrip line-microstrip line slotline coupling transition structure,and investigates the influence law of circuit structure parameters such as feed point position and feed line length on the electromagnetic resonant modes of the coupling structure,which provides the theoretical basis for the design of subsequent broadband and ultra-broadband slotline coupling transition structures.(2)Based on the analysis of microstrip line-microstrip line slotline coupling transition structure,the excitation mechanism of higher secondary modes in slotline resonators is studied in detail,and three broadband microstrip line-microstrip line slotline coupling transition structures are designed.Firstly,based on the conventional uniform double-slotline coupling transition structure,a T-shaped microstrip branch line slotline coupling transition structure is proposed and designed.It is found that two resonant modes are excited when the T-shaped branch line is located at the center of the slotline.Where the whole passband response can actually be regarded as the superposition of the frequency response of the two resonant modes.The transition structure has a return loss better than-10 d B and an insertion loss greater than-6.6 d B in the passband of 87.5-101.3 GHz.In comparison with the simulation results,the test results are shifted toward the lower frequencies and the return loss matching has deteriorated to a certain extent.The simulation analysis shows that it is mainly due to the softening and thinning of the bonding sheet by the press fit of the multilayer-based LCP substrate during the processing and fabrication of the transition structure.In order to stimulate and use more modes of the resonator,two microstrip branch lines loaded slotline transition structures have been designed and implemented.One of them is a microstrip branch loaded slotline tri-mode resonator coupling transition structure,which is better than-2.4 d B insertion loss and better than-13 d B return loss in the 48.8～75.46 GHz band after using the conventional parallel coupling feed;the other one is a microstrip branch loaded slotline four-mode resonator coupling transition structure,using dual parallel microstrip branch loading,the transition structure in the 41.56～63.29 GHz band,the insertion loss is greater than-4.43 d B,the return loss is better than-6.3 d B.The three transition structures are processed and fabricated,and the test results show good broadband characteristics.(3)Based on the microstrip line-microstrip line slotline coupling transition structure,two ultra-wideband slotline coupling transition structures are designed and implemented.First,based on the conventional ring resonator uniform dual slotline coupling transition structure,a ring resonator back-to-back Y-type slotline coupling transition structure is proposed and designed.The insertion loss of this transition structure is about-2.2 d B in the43.53～104.5 GHz band,and the minimum/maximum loss is-1.6/-5.3 d B,and the return loss in the passband is better than-11.9 d B,and its relative bandwidth can reach 82.3(4).In order to further reduce the size of this slotted line coupling transition structure,an H-shaped slotline coupling transition structure is proposed and designed.The improved transition structure has an insertion loss of about-2.3 d B and a min/max loss of-1.5/-4.6 d B in the43.13～113.39 GHz band,and the return loss in the passband is better than-11.78 d B,and the relative bandwidth can reach 89.7(4).Both structures were processed and fabricated,and the test results showed excellent ultra-wideband characteristics. |
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