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What role do directional couplers play in microwave systems?
In today’s microwave practice, the directional coupler has become a virtually indispensable measurement tool. It provides a simple, convenient, accurate means for sam- pling microwave energy without moving parts and without the need for adjustments.
What is a coaxial directional coupler?
A directional coupler is a measurement device that is inserted into the transmission line between an RF source—such as a signal generator, vector network analyzer, or transmitter—and a load. The source is generally connected to the coupler’s input port and the load to the output or transmitted port.
What are the functions of a directional coupler?
Directional Couplers: This type of coupler has three accessible ports, as shown in Fig. 2, where the fourth port is internally terminated to provide maximum directivity. The basic function of a directional coupler is to sample the isolated (reverse) signal. A typical application is measurement of reflected power (or indirectly, VSWR).
Which is the isolated port on a directional coupler?
Looking at the generic directional coupler symbol below, if port 1 is the incident port, port 2 is the through port (because it is connected with a straight line). Port 3 is the coupled port, and port 4 is the isolated port. For a signal incident on port 2, port 1 is the through port, port 4 is the coupled port and port 3 is the isolated port.
What does directivity mean on a coupler circuit?
Directivity: This is a measure of the coupler’s ability to separate waves propagating in forward and reverse directions, as observed at the coupled (P3) and isolated (P4) ports Isolation: Indicates the power delivered to the uncoupled load (P4)
What kind of response does a symmetric coupler provide?
Asymmetric multi-section coupled structures provide forward-wave, in-phase response, while symmetric multi-section couplers provide backward-wave, quadrature response. Try to remember that for the upcoming quiz… Don’t get hung up on the port nomenclature, there is no “standard” way to number the ports.