1. Quarter wave transformers cannot be used for non-TEM lines for impedance matching.
a) True
b) False
Explanation: For non-TEM lines, propagation constant is not a linear function of frequency and the wave impedance is frequency dependent. These factors complicate the behavior of the quarter wave transformer for non-TEM lines.
2. The reactances associated with the transmission line due to discontinuities:
a) Can be ignored
b) Have to matched
c) Discontinuities do not exist
d) None of the mentioned
Explanation: Reactance due to discontinuities in the transmission line contribute to the impedance, they can be matched by altering the length of the matching section.
3. If a load of 10Ω has to be matched to a transmission line of characteristic impedance of 50Ω, then the characteristic impedance of the matching section of the transmission line is:
a) 50Ω
b) 10Ω
c) 22.36Ω
d) 100Ω
Explanation: Characteristic impedance of the matching section of a transmission line is given by Z1=√Zₒ.ZL. Substituting the given impedance values, the characteristic impedance of the matching section is 22.36 Ω.
4. The passband response of a binomial matching transformer can be called optimum:
a) if the roll off in the response curve is high
b) if the response is flat in the impedance matched region
c) if the matching network is frequency sensitive
d) none of the mentioned
Explanation: The response curve of a binomial matching transformer ( θ v/s │Г (θ) │) must be flat at the frequency for which impedance matching is performed and for those frequencies that lie in the required bandwidth. This is one of the most important characteristic of a good matching circuit.
5. If a quality binomial matching transformer gives a good flat response curve, it is called “maximally flat”.
a) true
b) false
Explanation: A binomial matching section can be termed efficient when it is less frequency sensitive and gives a constant gain over a wide range of frequencies. This constant gain implies a flat curve over a wide range of frequencies. This is termed as “maximally flat”.
6. The response curve of a binomial matching transformer is plotted for each section of the matching network individually and then analyzed for optimum solution.
a) true
b) false
Explanation: The response curve of a binomial multisection transformer is determined for an N-section transformer by setting the first N-1 derivatives of │Г (θ) │ to zero at the center frequency, fₒ.
7. The reflection co-efficient magnitude of a binomial multisection transformer is:
a) 2N│A││cos (θ)│N
b) 2N│A│
c) 2N│cos (θ) │N
d) none of the mentioned
Explanation: The reflection co-efficient of a binomial multisection transformer is dependent on the length of the matching section, operating frequency and load impedance and characteristic impedance. A is a constant defined as A=2-N (ZL– Z0)/ (ZL+ Z0).
8. In the plot of normalized frequency v/s reflection co-efficient for a binomial multisection filter, the curve has a dip at:
a) center frequency
b) upper cutoff frequency
c) lower cutoff frequency
d) none of the mentioned
Explanation: Since the impedance matching circuit is used to match the load to the transmission line, there will be perfect match in the circuit resulting in zero or low reflection. Hence, there is a dip at the center frequency.
9. As the number of sections in the binomial multisection transformer increases the plot of normalized frequency v/s reflection co-efficient has a wider open curve.
a) true
b) false
Explanation: When more number of sections are used for matching, the reflection co-efficient is low for neighboring frequencies as well. Hence, the network can be used for a wide range of operating frequencies. Hence, this increases the bandwidth.
10. To obtain a flat curve in the response of a binomial multisection transformer, N-1 derivatives of │Г (θ) │are set to zero. This implies:
a) the frequency sensitivity of the matching section is increased linearly
b) the frequency sensitivity of the matching section is increased exponentially
c) roll off in the curve is increased
d) none of the mentioned
Explanation: The derivatives of │Г (θ) │ show the rate of change of reflection co-efficient with distance. If this derivative is not zero, the matching circuit becomes more sensitive and a higher bandwidth cannot be obtained. Hence to make the matching network frequency independent, the derivatives are set to zero.