1. Which of the following statement is false regarding Type-1 Sleeve Balun?
a) It is shorted at the base
b) It has a λ/4 sleeve
c) It has a λ/2 sleeve
d) Ideally it provides infinite impedance at top
Explanation: Sleeve Balun has a λ/4 sleeve which is shorted at base electrically and it provides infinite impedance at the top.
2. Consider a 9:1 Balun (unbalanced to balance conversion); if the unbalanced impedance is RΩ then the balanced impedance will be _____Ω.
a) 9R
b) 3R
c) 0.11R
d) 0.45R
Explanation: A 1:9 Balun represents that the balanced impedance is 9 times the unbalanced impedance.
⇨ Balanced impedance =9×R=9R
3. Which of the following Balun changes the shape of the unbalanced transmission line to that of a balanced transmission line?
a) Sleeve Balun
b) Folded Balun
c) Tapered Balun
d) Infinite Balun
Explanation: Tapered Balun changes the shape of the unbalanced transmission line to that of a balanced transmission line. Sleeve Balun uses a λ/4 sleeve which is shorted at base electrically and it provides infinite impedance at the top. Infinite Balun uses the current flowing outside the conductor as a part of antenna.
4. In which of the following Balun we don’t choke the current?
a) Sleeve Balun
b) Folded Balun
c) Tapered Balun
d) Infinite Balun
Explanation: Infinite Balun uses the current flowing outside the conductor as a part of antenna. In this we don’t choke the current, but we use it as a part of antenna, where we want the current flow in it.
5. Which of the following Balun contains a sliding short circuit bar for frequency adjustment?
a) Type – 1
b) Sleeve Balun
c) Type – 2
d) Type – 3
Explanation: Type – 3 Baluns has a sliding short circuit bar for frequency adjustment. Sleeve Balun or Type -1 Balun has a λ/4 sleeve which is shorted at base electrically.
6. Type II Balun has two Type I balloons in series providing more bandwidth and load impedances at all frequencies.
a) True
b) False
Explanation: Type II Balun has 2 Type I Baluns in series providing more bandwidth and load impedances at all frequencies. Type -1 Balun has a λ/4 sleeve which is shorted at base electrically.
7. Reciprocity applies to which of the following devices?
a) Isolator
b) Circulator
c) Balun
d) RF amplifiers
Explanation: In a Balun, a 3 port network, contains one matched input and two differential outputs. It is used to convert the unbalanced signal to balanced and vice-versa. So it is reciprocal. Isolator, Circulator, RF amplifiers are Non reciprocal devices.
8. For a Balun to work effectively, it must have ____ impedance for common mode currents and ____ impedance for differential mode current.
a) high, low
b) low, high
c) high, high
d) low, low
Explanation: Since Balun have to minimize the common mode currents it should have High impedance.
For differential mode currents it must have low impedance.
9. Which of the following polarization is used in monopole antenna?
a) Right-hand Circular
b) Linear
c) Depends on the feed
d) Left-hand Circular
Explanation: The linear polarization takes place in the monopole dipole. In the Dipole also a linear polarization takes place. Parabolic reflectors take the polarization of the feed. In helical, circular loop antennas we can find the circular polarization.
10. Which type of polarization is found in parabolic reflector?
a) Right-hand Circular
b) Linear
c) Depends on the feed
d) Left-hand Circular
Explanation: The parabolic antennas take the polarization of the feed. The linear polarization takes place in the monopole dipole. In the Dipole also a linear polarization takes place. In helical, circular loop antennas we can find the circular polarization.