1. If the normalized admittance at a point on a transmission line to be matched is 1+j1.47. Then the normalized susceptance of the stub used for shunt stub matching is:
a) 1Ω
b) 1.47 Ω
c) -1.47 Ω
d) -1 Ω
Explanation: When shunt stubs are used for impedance matching between a load and transmission line, the susceptance of the shunt stub must be negative of the line’s susceptance at that point for impedance matching.
2. After impedance matching, if a graph is plot with frequency v/s reflection co-efficient of the transmission line is done, then at the frequency point for which the design is done, which of the following is true?
a) There is a peak at this point of the curve
b) There is a dip at this point of the curve
c) The curve is a straight line
d) Such a plot cannot be obtained
Explanation: Since the plot is frequency v/s reflection co-efficient, after impedance matching the reflection co-efficient will be zero or minimum. Hence, there is a dip at that point of the curve.
3. In series stub matching, if the normalized impedance at a point on the transmission line to be matched is 1+j1.33. Then the reactance of the series stub used for matching is:
a) 1 Ω
b) -1.33 Ω
c) -1 Ω
d) 1.33 Ω
Explanation: The reactance of the series stub is negative of the reactance of the line at the point at which it has to be matched. That is, if the line reactance is inductive, the series stub’s reactance is capacitive.
4. The major disadvantage of single stub tuning is:
a) it requires a variable length of line between the load and the stub
b) it involves 2 variable parameters
c) complex calculation
d) none of the mentioned
Explanation: Single stub matching requires a variable length line between the stub and the load for matching which is a major disadvantage since the length of the stub plays a crucial role in matching.
5. The major advantage of double stub tuning is:
a) it uses 2 tuning stubs in fixed positions
b) it involves 2 stubs
c) length of the stub is variable
d) none of the mentioned
Explanation: The disadvantage of single stub tuning is overcome in double stub tuning. It uses 2 tuning stubs in fixed positions so that the length between the first stub and the load is not variable.
6. In a double stub tuner circuit, the load is of _______ length from the first stub.
a) fixed length
b) arbitrary length
c) depends on the load impedance to be matched
d) depends on the characteristic impedance of the transmission line
Explanation: The position of the first stub in a double stub tuner is variable from the load end. But the distance between the 2 stubs is fixed based on the value to which impedance is matched.
7. Double stub tuners are fabricated in coaxial line are connected in shunt with the main co-axial line.
a) true
b) false
Explanation: Most of the transmission lines used in most of the practical applications use coaxial cables, for which impedance matching of the load are done using double stub tuners which are made of coaxial cables for their best suited properties.
8. Impedance matching with a double stub tuner using a smith chart yields 2 solutions.
a) true
b) false
Explanation: Both single stub tuning and double stub tuning give two solutions. The intersection of the admittance and the 1+jb circle drew on the smith chart yields 2 points from which 2 solutions can be generated.
9. All load impedances can be matched to a transmission line using double stub matching.
a) true
b) false
Explanation: When a smith chart is used for impedance matching, if the normalized load admittance yL were inside the g+jb circle, no value of stub susceptance b1 could ever bring the load point to intersect with the 1+jb circle; this forms a forbidden range of admittance that cannot be matched.
10.The simplest method of reducing the forbidden range of impedances is:
a) increase the distances between the stubs
b) reduce the distance between the stubs
c) increase the length of the stubs
d) reduce the length of the stubs
Explanation: Reducing the distances between the stubs reduces the forbidden area in the smith chart which involves the load impedances that cannot be matched. Thus, more number of load impedances (range) can be matched to the transmission line.