# Microwave Engineering Questions and Answers – Aperture Coupling

This set of Microwave Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Aperture Coupling”.

1. The matched network is placed between:
b) source and the transmission line
d) none of the mentioned

Explanation: At microwave frequencies, for maximum power transmission, the characteristic impedance of the transmission line must be matched to the load impedance with which the line is terminated. Hence to match these impedances, the matched network is laced between load and transmission line.

2. When a transmission line is matched to a load using a matched network, reflected waves are present:
a) between the load and the matched network
b) between the matched network and the transmission line
c) between the source and the transmission line
d) between the matched network and source

Explanation: The matching circuit is used to match the transmission line and the load. This circuit prevents the reflection of the waves reaching the source. Hence, reflected waves are present between the load and the matched network.

3. Impedance matching sensitive receiver components may improve the _____ of the system.
a) noise
b) SNR
c) amplification factor
d) thermal noise

Explanation: SNR (signal to noise ratio) of the system defines the ratio of signal power to noise power. An increase in this value results in increase of the signal strength. Impedance matching certain sensitive receiver components helps in delivering maximum power to the load and increased signal strength.

4. One of the most important factors to be considered in the selection of a particular matching network is:
a) noise component
b) amplification factor
c) bandwidth
d) none of the mentioned

Explanation: Any type of matching network can ideally give a perfect match at a single frequency. But it is desirable to match a load over a band of frequencies. Hence, bandwidth plays an important role in the selection of the matching network.

5. The simplest type of matching network, L section consists of _______ reactive elements.
a) one
b) two
c) four
d) six

Explanation: As the name of the matching circuit indicates, ‘L’ section consists of 2 reactive elements, one element vertical and another horizontal. 2 types of ‘L’ sections exist. The best one is chose based on the normalized value of the load impedance.
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6. The major limitation of a lumped elements matching ‘L’ network is:
a) they are not equally efficient at higher frequencies as they are at lower frequencies.
b) size of the network
c) they restrict flow of current
d) none of the mentioned

Explanation: Since we use lumped elements like inductors and capacitors as the components of the matching network, they behave differently at frequencies higher than 1GHz, because of the frequency dependent factor of inductive and capacitive reactance. This is one of the major limitations.

7. An ‘L’ network is required to match a load impedance of 40Ω to a transmission line of characteristic impedance 60Ω. The components of the L network are:
a) 28.28+j0 Ω
b) 28.28+j1 Ω
c) 50Ω
d) 48.9Ω

Explanation: Since both load impedance and characteristic impedance are resistive (real), the imaginary part of the matching network is 0. Real part of the matching network is given by the expression ±√(RL(Z0– RL))-XL. Substituting the values given, the matching network impedance is 28.28Ω.

8. The imaginary part of the matching network is given by the relation:
a) ±(√(Z0– RL)/RL)Z00
b) ±(√(Z0– RL)/RL)
c) ±(√(Z0– RL)/ Z0
d) None of the mentioned

Explanation: By theoretical analysis, the expressions for real and imaginary parts of the impedance of the matching network are derived in terms of the load impedance and the characteristic impedance of the transmission line. This expression derived is ±(√(Z0– RL)/RL)Z0 .

9. Which of the following material is not used in the fabrication of resistors of thin films?
a) nichrome
b) tantalum nitride
c) doped semiconductor
d) pure silicon

Explanation: Certain physical properties are to be met in order to use a material to make thin film resistors. These properties are not found in pure silicon which is an intrinsic semiconductor.

10. Large values of inductance can be realized by:
a) loop of transmission line
b) spiral inductor
c) coils of wires
d) none of the mentioned

Explanation: Loop of transmission lines are used to make inductors to realize lower values of inductance. Coils of wires cannot be used to realize inductors at higher frequencies. Spiral conductors can be used to realize inductors of higher values at higher frequencies.

11. A short transmission line stub can be used to provide a shunt capacitance of:
a) 0-0.1µF
b) 0-0.1pF
c) 0-0.1nF
d) 1-10pF

Explanation: Since a transmission line consists of two wires, which can act plates of a capacitor, they can be used as a capacitor of very low values of the range 0-0.1pF.

Sanfoundry Global Education & Learning Series – Microwave Engineering.
To practice all areas of Microwave Engineering, here is complete set of 1000+ Multiple Choice Questions and Answers.

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