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Given a range of frequencies, which of the following systems is best for transmission line load matching ?

Given a range of frequencies, which of the following systems is best for transmission line load matching ? Correct Answer Double stub

In the question, it is given that impedance matching for the “Range of frequency” it means the frequency is varying.

In the case of Single stub or Quarter wave transformer matching if the frequency changes then we will have to change the location of the stub which is not suitable so the Double stub matching technique will be best for this case.

Important Points

Stub matching

 A stub is a length of transmission line or waveguide that is connected at one end only.

Stubs can be used to match a load impedance to the transmission line characteristic impedance.

The stub has positioned a distance from the load.

This distance is chosen so that at that point the resistive part of the load impedance is made equal to the resistive part of the characteristic impedance by impedance transformer action of the length of the mainline.

The length of the stub is chosen so that it exactly cancels the reactive part of the presented impedance. This is known as Stub Matching.

Single-stub method for impedance matching:

An arbitrary load impedance can be matched to a transmission line by placing a single short-circuited stub in parallel with the line at a suitable location. A single stub will only achieve a perfect match at one specific frequency.

Double stub matching:

 In this method, we use two stubs in which the locations of the stub are arbitrary, the two stub lengths furnishing the required adjustments. This is called double stub matching.

Double stub matching is preferred over single stub due to the following disadvantages of the single stub.

1. Single stub matching is useful for a fixed frequency. So as frequency changes the location of a single stub will have to be changed.

2. The single stub matching system is based on the measurement of voltage minimum. Hence for the coaxial line, it is very difficult to get such voltage minimum, without using a slotted line section.

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