IGNOU PHE 16 2018 - Explain the construction and working of a directional coupler used in

Question

Explain the construction and working of a directional coupler used in microwaves.

How does its function differ from an isolator?

25 Jan 2018

Answer :

Word Count : 509

A Directional coupler is a device that samples a small amount of Microwave power for measurement purposes. The power measurements include incident power, reflected power, VSWR values, etc.

Directional Coupler is a 4-port waveguide junction consisting of a primary main waveguide and a secondary auxiliary waveguide. The following figure shows the image of a directional coupler.

Image ignouacademy-com--p-academy-75486

Directional coupler is used to couple the Microwave power which may be unidirectional or bi-directional.

Properties of Directional Couplers

The properties of an ideal directional coupler are as follows.

All the terminations are matched to the ports.

When the power travels from Port 1 to Port 2, some portion of it gets coupled to Port 4 but not to Port 3.

As it is also a bi-directional coupler, when the power travels from Port 2 to Port 1, some portion of it gets coupled to Port 3 but not to Port 4.

If the power is incident through Port 3, a portion of it is coupled to Port 2, but not to Port 1.

If the power is incident through Port 4, a portion of it is coupled to Port 1, but not to Port 2.

Port 1 and 3 are decoupled

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