Design And Implementation Of30MHz-512MHz Broadband Strip Line Directional Coupler

In modern communication and microwave systems, directional couplers have a widerange of applications, and become an important part of many microwave circuits. Withthe rapid development of communication technology, the targets of directional couplershave become more and more high, and we hope directional couplers have widerbandwidth, smaller size, higher directivity and better reliability. Because of theadvantages of small size and broadband, the coupled strip line directional couplersbecome a research hotspot. I use the coupled strip line structure to design directionalcoupler in this paper.In this paper I complete the design of strip line directional coupler, and its operatingfrequency is30MHz-512MHz, coupling is50dB, directivity is more than13dB, coupledflatness is±0.7dB, VSWR is less than1.25, IL is less than0.25dB, the required size isless than40mm×30mm×10mm. In order to meet the target, the final design uses the threecoupled strip line structure, and adds attenuation network to achieve the coupled flatnessrequirement.First, working principle and technical indicators of directional couplers areintroduced. Since the coupled strip line structure is built on the basis of the strip line, sothe structure and fundamental characteristics of the strip line are analyzed. Then Idescribe the method of analyzing coupled strip line in detail, which is odd and even modeanalysis method. The relationship between the coupling coefficient and the odd and evenmode characteristic impedances is given, and the odd and even mode characteristicimpedances or admittances of several common coupled strip line structures are derived.Finally, I focus on the design of the coupled strip line directional coupler. Accordingto the technical requirements, the solution design is determined, and the coupled stripline structure sizes are calculated. Then the circuit simulation (ADS) and modelingsimulation (HFSS) are finished, and the parameters of structure sizes are verified.Production samples are produced and tested by vector network analyzer. The results of the test show that the designed directional coupler has met the requirements.