# Antennas Questions and Answers – Types of Baluns

This set of Antennas Question Bank focuses on “Types of Baluns”.

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.
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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.

Sanfoundry Global Education & Learning Series – Antennas.