Ensuring RF applications are functioning correctly requires proper monitoring and controlling of RF power levels. Such applications also benefit from wide frequency ranges and methods to monitor standing wave ratio while the instrument is operating. However, this is difficult to achieve without incurring losses in transmission power.
In especially demanding RF environments, such as communications or electronic warfare, high losses in transmission lines and loads cannot be tolerated. Therefore, we need some device that will provide accurate and efficient measurements with minimal loss and other interference.
Directional couplers are RF components that are employed in transmission lines to both monitor RF power levels and direct a portion of power to other parts of the system; the incoming power to the coupler can be divided and part of it used for another application.
The standard four-port directional coupler consists of two coupled transmission lines, as shown in the figure below.
Each of the ports in the figure are numbered 1 to 4 and labeled with their respective functions. There are two coupled transmission lines as represented by the parallel horizontal lines. Power enters from the main transmission line through port 1 (input port), and exits through port 2 (output port). A portion of the power couples from the main transmission line to the secondary transmission line to port 3 (coupled port). A minute amount of reflected power may travel in the direction of the isolated port, which is typically terminated.
The coupler is also symmetrical, or bi-directional, meaning power can be input through port 2 to output through port 1. In this case, the coupled port would be port 4 and the isolated port is port 3.
Directional couplers are used extensively in electronic warfare, electronic countermeasures, electronic counter-countermeasures (ECCM), and instrumentation.
Manufacturers in RF and microwave components typically offer directional couplers as a product. When browsing for couplers, make sure to check that they are compliant with US specifications and international standards. In particular, attention should be given to frequency range, VSWR, Insertion Loss, and especially directivity as they directly reflect the accuracy of any measuring instrument.
ET Industries’ stripline directional couplers meet stringent specifications such as high directivity, low VSWR, and a wide frequency range. We offer couplers at various coupling values that are available with the appropriate coaxial connectors, including SMA, K, 2.4mm, 1.85mm, and N-type. ETI directional couplers achieve the highest electrical performance in the industry and are perfectly suited for the most demanding engineering applications.
ETI is an original manufacture of RF components. All products are manufactured in our factory in New Jersey
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