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Directional couplers are usually used for measurement and measurement applications. In this case, the input power and the reflected power of the transmission line are measured by using a dual directional coupler, or by using a directional coupler for multiple tests. After removing the loss of the coupler itself, it can be used as a measure of voltage Bobbi. Other uses include signal sampling, signal injection, and power flux monitoring. In order to achieve the best accuracy, users have to consider the loss of the directional coupler itself.
When precise measurements are taken, the isolation between ports should also be considered according to the quality of directional couplers. In any case, there is a certain degree of leakage between the ports of the coupler. This leakage is usually called isolation degree, which is used to measure the leakproof capacity of coupler design. Directional coupler's directivity is the ratio of isolation to coupling coefficient, which is a common performance index of coupler.
As with most RF / microwave devices, the exact values of device parameters are not always consistent at different frequencies. These coupling coefficients, insertion loss, orientation and isolation are all frequency factors. The above factors and all manufacturing tolerances must be taken into account when conducting high sensitivity measurements. In addition, the directional coupler also has the parameter of working bandwidth. In design, tradeoffs between the parameters mentioned above are needed, so the optimal design of the coupler ultimately depends on its application.
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