Design Of Transitional Structure And Device Based On Microwave Transmission Line

With the rapid development of microwave circuits,the combination of different transmission lines has become a norm.Microstrip line as today's mainstream transmission line,often combined with other plane transmission line.Among them,the transition of microstrip line-slot line is the most common.With the advent of the era of 5G mobile communication,microwave components such as filters,power splitters and directional couplers which are composed of microstrip lines and slot lines are superior in performance and are easy to integrate with other microwave components.First of all,The basic theory of microstrip line,coupled microstrip line and slot line is introduced.Secondly,a miniaturized coupling microstrip line directional coupler is designed.The differences between the proposed couplers from the traditional ones are that the coupling uses two semi-circular arcs,and the radii of the two semi-circular arcs is different.The directional coupler improves the directionality and isolation by adding microstrip open-circuit branches at the isolation port.The HFSS software simulation shows that the coupler performance is good,which shows that this design method is feasible.Thirdly,a kind of microstrip line-slotline transition structure is improved.On the basis of that,a microstrip-slotline transition structure with notch characteristics is successfully designed.The improved back-to-back microstrip line-slotline transition structure adopts cross-finger slotline instead of traditional straight slotline,and uses the ring-type and petal-type short circuit terminal instead of fan-type short circuit terminal.The top layer of the dielectric layer is two microstrip lines with fan-shaped open ends,and the bottom is a cross-finger slotline perpendicular to the microstrip line.When the microstrip line open terminal fan angle and the slot ring short circuit terminal width(groove line petal short semi-axis)changes,and the slotted line is straight line or interdigital,we use HFSS software to analyse these factors' impact on the transitional structure performance.Simulation results show that the proposed VSWR and S-parameters are superior to the traditional ones.Based on the petal-type and back-to-back microstrip line-slotlne transition structure,a dual-band notch characteristics of the transitional structure is designed.To match the 50? microstrip line,4 Chebyshev impedance transformations are used in the transition structure,and a U-shaped slot is etched on its strip to achieve the notch characteristics.By changing the length of the slot,the trap frequency band can be offset.The measured results of notch characteristics structure are consistent with the simulation results,indicating the structure design is correct.The notch characteristic transition structure can be used in a 5G communication system.Finally,a power divider based on the transition structure of microstrip-slotline is designed.The transmission and distribution of signal power is realized by using the microstrip-slotline transition structure and slotline-microstrip transition structure;At the microstrip-slotline transition structure,two fan-shaped microstrip radial lines,which are symmetrical to the groove and connected to the output port of the microstrip,play a role in isolating the impedance.Through the simulation of HFSS software,it is known that the output ports' isolation of the the power divider has been improved.