Impedance Matching Questions and Answers

Q: Assertion (A) : A stub is shorted or open section of transmission line used inconjunction with transmission line.Reason (R) : A stub cancel out reflections and provide impedance match.

The keyed answer is both (A) and (R) are true but (R) is not the correct explanation of (A).A describes what a stub is: a length of transmission line, short-circuited or open-circuited at its far end, connected in shunt or series with the main line. R describes what a stub does in single- and double-stub matching: its reactance cancels the reactive part of the load seen at that point, removing reflections and matching the line.Both statements are true. But a definition is not explained by an application: what makes something a stub is its construction, not the use it is put to (stubs are also used as filters and resonators). That is why R is not taken as the explanation of A.

Q: The stub length on single stub matching cancels :

The stub cancels the susceptance.In single stub matching the stub is placed at the point on the line where the normalised admittance is 1 + jb, so that its conductance already matches the line. A short- or open-circuited stub of suitable length adds a susceptance of −jb, cancelling the unwanted susceptance and leaving a matched admittance of 1.The conductance is matched by choosing the stub's position, not by the stub. Permeability is a property of the medium, and the stub works in admittance terms on the shunt susceptance, not on an inductance as such.

Q: We say transmission is matched when :

A line is matched when \(Z_L = z_0\).When the load impedance equals the characteristic impedance of the line, the reflection coefficient is zero:\[ \Gamma = \frac{Z_L - Z_0}{Z_L + Z_0} = 0 \]All the incident power is absorbed by the load, there is no reflected wave, and the VSWR is 1.A load of \(Z_0/2\) or \(2Z_0\) gives a reflection coefficient of magnitude 1/3 and a VSWR of 2. \(\sqrt{Z_0}\) is not even dimensionally an impedance, so it cannot be a matching condition.

Direction for [ Question No: 1 To 1 ] :

Assertion-Reason type questions : The following items consist of two statements, one labelled as 'Assertion (A)', and the other labelled the 'Reason (R)'. You are to examine these two statements and decide if the Assertion (A) and the Reason (R) are individually true and if so, whether the reason is a correct explanation of the Assertion. Select your answer to these items using the codes given below and mark your answer sheet accordingly.

Codes :
(A) Both (A) and (R) are true and (R) is the correct explanation of (A)
(B) Both (A) and (R) are true but (R) is not the correct explanation of (A)
(C) (A) is true but (R) is false
(D) (A) is false and (R) is true

Assertion (A) : A stub is shorted or open section of transmission line used inconjunction with transmission line.

Reason (R) : A stub cancel out reflections and provide impedance match.

A.Both (A) and (R) are true and (R) is the correct explanation of (A)
B.Both (A) and (R) are true but (R) is not the correct explanation of (A)
C.(A) is true but (R) is false
D.(A) is false and (R) is true

Exam Year(s)

MH SET - 2018, SET Exam - 2018,

Answer: B

The keyed answer is both (A) and (R) are true but (R) is not the correct explanation of (A).

A describes what a stub is: a length of transmission line, short-circuited or open-circuited at its far end, connected in shunt or series with the main line. R describes what a stub does in single- and double-stub matching: its reactance cancels the reactive part of the load seen at that point, removing reflections and matching the line.

Both statements are true. But a definition is not explained by an application: what makes something a stub is its construction, not the use it is put to (stubs are also used as filters and resonators). That is why R is not taken as the explanation of A.

Discuss in Forum

The stub length on single stub matching cancels :

A.Susceptance
B.Permeability
C.Conductance
D.Inductance

Exam Year(s)

MH SET - 2020, SET Exam - 2020,

Answer: A

The stub cancels the susceptance.

In single stub matching the stub is placed at the point on the line where the normalised admittance is 1 + jb, so that its conductance already matches the line. A short- or open-circuited stub of suitable length adds a susceptance of −jb, cancelling the unwanted susceptance and leaving a matched admittance of 1.

The conductance is matched by choosing the stub's position, not by the stub. Permeability is a property of the medium, and the stub works in admittance terms on the shunt susceptance, not on an inductance as such.

Discuss in Forum

We say transmission is matched when :

A.\(Z_L = z_0\)
B.\(Z_L = \sqrt{z_0}\)
C.\(Z_L = z_0/2\)
D.\(Z_L = 2z_0\)

Exam Year(s)

MH SET - 2023, SET Exam - 2023,

Answer: A

A line is matched when \(Z_L = z_0\).

When the load impedance equals the characteristic impedance of the line, the reflection coefficient is zero:

\[ \Gamma = \frac{Z_L - Z_0}{Z_L + Z_0} = 0 \]

All the incident power is absorbed by the load, there is no reflected wave, and the VSWR is 1.

A load of \(Z_0/2\) or \(2Z_0\) gives a reflection coefficient of magnitude 1/3 and a VSWR of 2. \(\sqrt{Z_0}\) is not even dimensionally an impedance, so it cannot be a matching condition.

Discuss in Forum

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Impedance Matching Questions and Answers

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