Research And Design Of Directional Coupler On Defected Ground Structure

As a basic component of microwave RF circuit,directional coupler has always been one of the reserch focuses and hot spots.Nowadays,under the mutual promotion of the development of mobile communication and the Internet of Things,people have higher requirements for the speed of information transmission,which makes the mobile communication system develop towards a higher microwave frequency band continuously,and the research and design of high-performance directional couplers become more urgent.Firstly,this thesis analyzes the basic theory of directional coupler,including the network analysis of directional coupler,technical indicators,etc.,and focuses on the odd-even mode analysis of coupling line coupler and ring directional coupler.Then,this thesis analyzes the structural characteristics and amplitude-frequency characteristics of three common Defected Ground Structures(DGS),and focuses on the methods of extracting the equivalent circuits of DGS structures and the basic characteristics of DGS structures.These provide a theoretical basis for the design of DGS directional couplers.Then,DGS structure is introduced to the traditional single-section microstrip coupled line coupler to improve the coupling degree of the coupler.On the basis,open-circuit branches are added on the coupling section of the coupler to further improve the directivity of the coupler,then a high directivity microstrip line directional coupler whose coupling degree is 6dB are designed.The working frequency of the designed microstrip line directional coupler is 4.5GHz,in the center frequency,S11 is-42.35dB,S41 is-35.35dB,the directivity is 29.27dB,and the coupling is 6dB.All the parameters meet the requirements of the indicators.Then the coupler is manufactured and measured.The results are basically consistent with the simulation results and realize the purpose of enhancing the coupling degree and directivity of the coupler.Finally,a miniaturized rat-race directional coupler with harmonic suppression is designed based on the traditional rat-race directional coupler.First,T-type transmission line is introduced into the traditional rat-race coupler to achieve the effect of miniaturization and harmonic suppression.On the basis of this,rectangular DGS structures are etched on the floor of the coupler,which improve the impedance of the microstrip line,widen the width of the microstrip line,and ensure the realization of the processing.At the center frequency of the coupler,2.2GHz,S11 is-39.59dB,S41 is-54.26dB,S21 is-3.034dB,S31 is-3.036dB,?S21-?S31 is 0.536°,and ?S24-?S34 is-179.43°,all reach the design goal.In the frequency range of 3.5GHz?21GHz,the transmission is suppressed below-10dB,the suppression bandwidth is wide,and the volume of the designed coupler is only 28%of the traditional rat-race coupler.Moreover,the designed coupler is processed and tested,and the results are basically consistent with the simulation results,which verify the effectiveness of the design.