The current for outgoing will be opposite to the current for reflecting. If we sample the current with a current transformer, then the voltage will be opposite. Now we can arrange for the voltage on the line to cancel out the current sample in one direction, and add to it in the other. Well it is isn't it? The waveguide component that does this is called a magic T and its just some pipe.
How do they do that? There ain't half been some clever bastards. A directional coupler can be a splitter and a combiner as well, depending on how it is used. When the coupled port is exposed instead of terminated with some R, then you have a 4 port bidirectional splitter with good isolation and low reflectance when match terminated.
To get wider bandwidths , there are various tricks. A magnetic transformer is often used with bifilar wound hydbrid ferrite core is used. Depending on mutual coupling impedance, the coupler can be a -3dB tap - 0. Also they can be equal power taps. This one can split 5kW at one frequency. Isolation is the cancellation of Mutual coupling.
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Forgot Password? Don't have an account? Sign Up. Full Name:. Your company name:. Getting Media Kit. Cancel Download. Image Link. Cancel Save. Note: File Size should be less than 10MB. Please Wait!!! Your Query has been successfully submitted. When connected in reverse, the coupled port provides a sample of the output forward signal , attenuated by the coupling factor. This sample can be used for waveform monitoring, spectrum analysis, and other test and measurement functions.
The sample may also be used to drive feedback circuitry. One important application of this type is leveling the amplitude of a signal generator, providing a constant signal source for a test system. Figure 9: Schematic of a 3-port directional coupler in a levelled generator setup. The test signals for 2-tone testing may be combined in either a directional coupler or a power combiner.
Both methods will provide the necessary isolation between the signal sources. Figure Schematic of a 3-port directional coupler in a receiver intermodulation test setup. Although reflected power or VSWR is important, it may be more useful to simultaneously sample both forward and reflected signals. This function is provided by a bi-directional coupler, which allows monitoring or measurement of output power forward and reflected power reverse.
Built-in test BIT systems, production testing, and routine operational monitoring all benefit from bi-directional coupling.
This is a circuit element that provides measurement of forward power and reflected power typically calibrated as VSWR. This is a common, and highly useful, test function in RF laboratory and production test environments. As noted above, and in Fig. This provides isolation that eliminates the effects of mismatch of one path on the other path. The typical use of bi- and dual direction couplers is the reflectometer. Ports 3 and 4 may even have smaller connectors to distinguish them from the main line ports of the RF coupler.
Often the isolated port is terminated with an internal or external matched load which would typically be 50 ohms. While specific ports are given labels on a device, this is normally more of a physical constraint as some ports will be manufactured to carry higher powers than others. In fact any port can be the input, and this will result in the directly connected port being the transmitted port, the adjacent port being the coupled port, and the diagonal port being the isolated port.
As with any component or system, there are several specifications associated with RF directional couplers. The major RF directional coupler specifications are summarised in the table below. Couplers are not as widely used as some RF components like attenuators, mixers and the like, but in areas closer to the antenna where power may need to be sampled, they are widely used.
For example a directional coupler may be used within a meter detecting the standing wave ratio, but they also have many other applications.
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