1. Scattering matrix for a lossless matrix is:
a) Unitary
b) Symmetric
c) Identity matrix
d) Null matrix
Explanation: For a lossless network, the scattering matrix has to be unitary. That is, the law of conservation of energy is to be verified for this case. Using appropriate formula, this condition can be verified.
2. If the reflection co efficient of a 2 port network is 0.5 then the return network loss in the network is:
a) 6.5 dB
b) 0.15 dB
c) 6.020 dB
d) 10 dB
Explanation: Given the reflection coefficient of the network, return loss of the network is calculated using the formula -20 log │Г│. Substituting for reflection coefficient, the return loss of the network is 6.02 dB.
3. If the reflection co efficient of a 2 port network is 0.25 then the return network loss in the network is:
a) 12.05 dB
b) 0.15 dB
c) 20 dB
d) 10 dB
Explanation: Given the reflection coefficient of the network, return loss of the network is calculated using the formula -20 log │Г│. Substituting for reflection coefficient, the return loss of the network is 12.05 dB.
4. The matched network is placed between:
a) load and transmission line
b) source and the transmission line
c) source and the load
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.
5.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.
6. 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.
7. 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.
8. 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.
9. 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.
10. 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.