Coupler is one of the essential components in wireless mobile communication system.The size of microstrip coupler designed by classical coupler theory will change with frequency,about a quarter wave-length.Its directionality index is generally poor,only about 5 dB in the simulation in this paper.By changing the structure of the microstrip coupling line,the directionality index can exceed 20 dB while ensuring the stand-ing wave performance of the port.In this paper,the factors affecting the size and directivity of the coupler are analyzed theoretically,and a design method of a small size and high directivity microstrip coupler is proposed.HFSS is used to analyze the model and the actual production verifies its expected effect.
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