# Microwave Engineering Questions and Answers – Single Stage Transistor Amplifier Design

This set of Microwave Engineering online test focuses on “Single Stage Transistor Amplifier Design”.

1. The overall gain of a transistor is always a fixed value and cannot be changed as per design requirements.
a) True
b) False

Explanation: For a given transistor gain G0 is a fixed value and cannot be changed. But the overall transducer gain of the amplifier will be controlled by GS and GL, of the matching section used with the transistor.

2. The frequency response of an amplifier is _______
a) Wide band
b) Narrow band
c) Pass band
d) None of the mentioned

Explanation: Most transistors exhibit a significant impedance mismatch (large S11 and S22). This results in a frequency response of the transistor that being narrow band.

3. Maximum power transfer from the input matching port to the transistor will occur when:
a) Гin=Г*S
b) ГinS
c) ГinS. e
d) None of the mentioned

Explanation: For a transistor, ГS is the reflection co-efficient of the amplifier looking towards the source. Гin is the reflection coefficient of the amplifier looking towards the input terminals of an amplifier. For maximum power transfer, the above mentioned condition must be satisfied.

4. The condition for maximum power transfer from the transistor to the output matching network will occur when:
a) ГoutL*
b) ГoutL
c) Гout=1/ ГL
d) Гout=1/ ГL*2

Explanation: The condition for maximum power transfer from the transistor to the output matching network will occur when ГoutL*. ГL is the reflection coefficient seen looking towards the load. Гout is the looking towards the output ports of the transistor.

5. The input and output ports of an amplifier are always matched to the impedance Z0 .
a) True
b) False

Explanation: With two different matching techniques called conjugate matching and lossless matching sections, the input and output ports of a transistor are matched to the characteristic impedance Z0 of the feed line used.
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6. Unconditionally stable devices can always be ____________ for maximum gain.
a) Lossless matched
b) Conjugate matched
c) Forward biased
d) Driven with high current

Explanation: Unconditionally stable devices can always be conjugate matched for maximum power gain and potentially unstable devices can be conjugate matched if K>1 and │∆│<1.

7. The maximum transducer gain occurs when the source and the load are matched to the impedance Z of the transistor by lossless method.
a) True
b) False

Explanation: The maximum transducer power gain occurs when the source and load are conjugated matched to the transistor. This matched condition can be verified using the relation between the reflection coefficients.

8. Maximum transducer gain for an amplifier is the same as the maximum gain for an amplifier.
a) True
b) False

Explanation: Maximum transducer gain is also referred to as matched gain. Maximum gain does not give a meaningful result when the device is only conditionally stable, since the simultaneous conjugate match of the load and source is not possible simultaneously.

9. In terms of S parameters for a transistor, the transducer gain is given by the relation:
a) │S21│/│S12
b) │S12│/│S21
c) │S22│/│S11
d) │S11│/│S22

Explanation: Transducer power gain is defined as the ratio of power measured at the port 2 (output port) to the ratio of the power at the input port. This is redefined in terms of the S parameter of the network and can be written as │S21│/│S12│.

10. In the S matrix of a transistor, if the parameter S21 is 2.6 then the gain G0 of the transistor has the value
a) 6.2 dB
b) 8.3 dB
c) 2.22 dB
d) None of the mentioned

Explanation: Gain G0 of a transistor amplifier is given as 10 log S12. Substituting for S12 in the equation, then the gain G0 of the amplifier is given by 8.3 dB.

Sanfoundry Global Education & Learning Series – Microwave Engineering.
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