Design And Implementation Of30-150MHz Broadband Bi-Directional Coupler

With the rapid development of communication technology and increase of themicrowave system integration, the index requirements of various microwave devices isincreasing. Directional coupler as an important part of the transmission system, theoptimization of it’s performance has a very important significance for the microwavetransmission system. Directional couplers made by the transmission line transformers arewidely used in many microwave communication systems due to following advantages:small size, large power capacity, wide operating band, high directivity, simple structureand easy to be manufacted, etc. Therefore, this paper carries out a detailed study of thetransmission line transformer structure broadband bipolar directional coupler.In this paper I complete the design of transmission line transformer magic Tdirectional coupler, and its operating frequency is30MHz-150MHz, coupling is30dB,directivity is more than18dB, coupled flatness is±0.5dB, VSWR is less than1.25, IL isless than0.3dB, the required size is less than30mm×30mm×15mm. In order to meet thetarget, the final design uses transmission line transformers magic T with a series couplingtransformer and a shunt coupling transformer coupling structure, and adds attenuationnetwork to achieve the coupled flatness requirement.First, working principle and technical indicators of directional couplers areintroduced. Then make a analysis of the single directional coupler structure and improvedto obtain the final three-wire magic T coupler structure. In this paper, the couplingstructure is built on the basis of the transmission line transformer, transmission linetransformer is briefly introduced, and a detailed analysis of the potential characteristics aswell as the best transmission conditions of the three-wire transmission line transformers.Finally, the circuit simulation(ADS) are finished and optimize to solve the problemsin the simulation. Then, the coupler samples are produced according to the technicalrequirements,and be tested by network analyzer. Compared to the theoretical results, thereare some inadequacies, and give some improve suggestions.