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A synthesis method for a stripline-type branch-line 3-dB hybrid which is based on an equivalent circuit derived by the planar circuit approach is presented. The equivalent circuit of an ideal 3-dB hybrid is derived first from those of the segmented circuit elements, i.e., four three-port junctions and four quarter-wave transmission lines. A systematic synthesis process is then developed upon the basis of the equivalent circuit. Practical hybrid circuit having optimized circuit patterns which were constructed for center frequencies of 3, 5, and 7 GHz are discussed. Their measured characteristics are described. The results are shown to agree well with the theory, Article