| The directional couplers are widely applied in the microwave technology. In the rapid development of microwave integrated circuits and monolithic microwave integrated circuit, microstrip components are the core devices in the microwave system. Therefore, the performance of the directional coupler is the key to restricting system performance and technical standards. If the size of the equipment applied in communication system to be miniaturized, the corresponding requirement of the microwave devices is to achieve miniaturization. These are made to study the miniaturization of broadband directional couplers has important practical significance, and therefore reduce costs, improve performance and level of integration allows the miniaturization of the microstrip components theory to become the development trend.On the basis of the three branches of microstrip directional coupler, first we use the method of transmission line equivalent. The quarter-wavelength transmission line is equivalent to access terminal open circuit stubs so the area of the miniaturized coupler is46%of the traditional three branches of microstrip directional coupler. But the miniaturization of this approach is not satisfactory to the branch lines aside of the directional coupler. So we bend the branch lines to realize the miniaturization of the directional coupler. Take symmetrical T-type equivalent to the mainline, but the junction of the terminal open circuit stubs and the main line is very wide, it will increase the discontinuity of the microstrip line and affect the characteristics of directional coupler. So we make the open stubs further equivalent to be cross-shaped. The middle branch line is changed to two microstrip line connecting in parallel open stubs to reduce its length. Ultimately we get the area of the miniaturized coupler is39%of that of traditional three branches of microstrip directional coupler. We simulate the new coupler with the ADS software, the parameters meet the requirements. |
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