A directional coupler is a passive radio frequency device that uses value, which can extract a small portion of the energy from the main transmission path and guide it to one or more coupled ports. Since there is a high isolation between the coupling port and the main transmission path, the isolation between the orientation coupler ports is generally higher. Currently, there are two types of directional couplers with a coupling port and a termination coupler; and a dual-directional coupler having a forward and reverse coupling port. In addition, there are other types of binary couplers, which are referred to as a forward coupler and a reverse coupler depending on the type coupled to the coupling port of the forward or reverse port.
Common directional coupling
It is important to note that the coupling provided by the directional coupler has a direct impact on the theoretical minimum value of the main transmission path insertion loss. The smaller the coupling amount of the port, the lower the insertion loss. Typically, the rated power level of the coupling port is lower than the rated power level of the main transmission path, and when the difference between the main transmission path power and the coupling intensity exceeds the power processing capability of the coupled port, it may be faulty. In general, the orientation of the three-port orientation coupler using the precision internal matching terminal is higher than the four-port orientation coupler using the external termination mode.
Another factor that needs to be considered is the termination type of the directional coupler end port. If the end resistor is set to equal to the inherent impedance of the transmission line (usually 50 ohms), the energy at which the end port is extremely small reflectance. However, when the end port is shorted or opened, or when the characteristic impedance of the transmission line does not match, the energy at the port will be reflected back to the main transmission path. In addition, when the power limit of the terminal port is exceeded, a fault may occur. This situation will become particularly bad when the matching end port is invalidated and become reflected, which will cause destructive power levels in the main transmission path.
Directional couplers are typically used to test measurement applications. In this way, the input power and reflection power of the transmission line are measured by using a two-way coupler, or by performing multiple tests in a directional coupler. This can serve as a measure of the voltage stationbox after removing the losses of the coupler itself. Other uses include, for example, signal sampling, signal injection, and power flux monitoring, where the user has to consider the loss of the directional coupler itself in order to achieve the best accuracy.
When performing accurate measurement, it is also necessary to consider the isolation between the ports of the direction of the directional coupler. Regardless of the coupling, there is usually a certain degree of leaks between the coupler ports. This leakage is often referred to as isolation, which is used to measure the anti-leakage ability of the coupler design. The orientation of the directional coupler is the ratio of the isolation and coupling coefficient, and is a common performance index of the coupler.
Like most RF / microwave devices, the exact value of device parameters does not remain absolute at different frequencies. The above coupling coefficient, insertion loss, orientation, isolation, etc. are usually frequency factors. The above factors and all manufacturing tolerances must be considered when performing high sensitivity measurements. In addition, the directional coupler also has a work bandwidth. In design, we need to trade between the parameters mentioned above, so the optimal design of the coupler will eventually depend on its application.
Most directional couplers are grounded by port DC, and only some orientation couplers can allow DC current to pass. For a directional coupler that allows DC currents, it is important to keep the current below the rated value, which causes heat resistance or affecting termination performance. In order to meet the target performance, all ports of the dual-way coupler (or two-way coupler) must be grounded. In addition, it is important to match the grounding quality and connection load to the port impedance of the directional coupler.
The 90 degree or 180 degree bridge is also generally referred to as "coupler". Although these devices are typically similar to the orientation coupler, it is different from the orientation coupler. However, since this device can perform power allocation (3dB allocation) between the output and the coupled port, it is possible to cause damage when it is misfirmed as a directional coupling of the coupling coefficient.
Our other product:
