Design And Implementation Of Lumped Parameter Directional Coupler

With the development of modern communication technology, the Microwavesystem’s integration is improving, we also put forward higher index of directional coupler,which is the important part of the microwave system. So modern microwave equipmenthope directional couple have wide bandwidth, small size, high directivity and goodflatness. The lumped parameter directional couple which formed by mixed transformernetwork have obvious advantages to the distribution parameter directional couple. I usethe mixed transformer network to design directional coupler in this paper.In this paper I complete the design of two lumped parameter directional couples, andits operating frequency are1-30MHz and30MHz-200MHz,coupling is30dB, directivity ismore than18dB, coupled flatness is±0.6dB, VSWR is less than1.25, IL is less than0.25dB. In order to meet the target, the final design uses the tricyclic structure andtransmission line transformer structure, and adds attenuation network to achieve thecoupling degree requirement.First, working principle and technical indicators of directional couplers areintroduced. Since the lumped parameter directional couple is built on the basis oftransformer, so the lumped parameter transformer are introduced briefly, the structure andfundamental characteristics of the transformer are analyzed, and the general design stepsof transmission line transformer are given. Then I introduce the series and parallelcoupling analysis of transformer, derive the relationship between the tricyclic structuredirectional coupler’s main line attenuation and coupling degree and the number of coilturns.Finally, according to the technical requirements, I calculate the length of transmissionline and the number of coil turns based on theoretical analysis. Production samples areproduced and tested by vector network analyzer. The results of the test show that thedesigned directional coupler has met the requirements.