# Antennas Questions and Answers – Folded Dipole Antenna – Types

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This set of Antennas Questions and Answers for Campus interviews focuses on “Folded Dipole Antenna – Types”.

1. Which of the following statement is not correct?
a) Folded dipole antenna has less impedance than half dipole
b) Folded dipole is a balanced antenna
c) Folded dipole antenna is a dipole antenna with its end folded back forming a loop
d) Balun is used at the feeder when unbalanced feed is used in the folded dipole

Explanation: The impedance of folded dipole is four times the impedance of the half dipole. So its impedance is higher than the half dipole. Since folded dipole is a balanced antenna we use a balanced feeder so Balun is used.

2. Folded dipole antenna belongs to which type of antenna?
a) Reflector
b) Aperture
c) Lens
d) Wire

Explanation: Folded dipole antenna belongs to wire antenna. It is a dipole antenna with two ends folded back and connected to each other forming a loop.

3. What is the input impedance of a half wave folded dipole?
a) 73Ω
b) 292Ω
c) 146Ω
d) 36.5Ω

Explanation: The input impedance of a half wave folded dipole is four times the half wave dipole.
So Z= 4×73=292Ω

4. A half wave folded dipole of 3 wires has the impedance _____Ω.
a) 675
b) 657
c) 219
d) 292

Explanation: For a half wave folded dipole of 3 wires the impedance = n2×73=9×73=657

5. In which of the following type of folded dipole the number of conductors is varied?
a) Multi conductor folded dipole
b) Unequal conductor folded dipole
c) Both multi conductor and unequal conductor
d) Neither multi conductor nor unequal conductor

Explanation: In Multi conductor folded dipole, the two or more conductors are connected together. This increases the impedance and also the bandwidth.

6. In unequal conductor folded dipole, the diameter of the conductor of feed arm and the non feed arm are unequal.
a) True
b) False

Explanation: In unequal conductor folded dipole, the diameters of the two conductors connecting together are unequal. If the radii of two conductors are r1 (feed arm), r2 (non feed arm) and separated by a distance, then the impedance transformation for folded dipole is given by
$$Z = Z’\left(1+\frac{log⁡(\frac{a}{r1})}{log⁡(\frac{a}{r2})}\right)^2.$$

7. If the radii of two conductors are r1 (feed arm), r2 (non feed arm) and separated by a distance,then the impedance transformation for a half folded dipole is given by _______
a) $$\left(1+\frac{log⁡(\frac{a}{r1})}{log⁡(\frac{a}{r2})}\right)^2$$
b) $$73\left(1+\frac{log⁡(\frac{a}{r1})}{log⁡(\frac{a}{r2})}\right)^2$$
c) $$\left(1+\frac{log⁡(\frac{a}{r2})}{log⁡(\frac{a}{r1})}\right)^2$$
d) $$73\left(1+\frac{log⁡(\frac{a}{r2})}{log⁡(\frac{a}{r1})}\right)^2$$

Explanation: If the radii of two conductors are r1 (feed arm), r2 (non feed arm) and separated by a distance, then the impedance transformation for folded dipole is given by
$$Z = Z’\left(1+\frac{log⁡(\frac{a}{r1})}{log⁡(\frac{a}{r2})}\right)^2$$
For a half dipole Z’=73Ω
∴ $$Z = 73\left(1+\frac{log⁡(\frac{a}{r1})}{log⁡(\frac{a}{r2})}\right)^2$$

8. For a multi conductor folded dipole with n conductors, the impedance is ____ Ω.
a) 2n Z
b) nZ
c) n2Z
d) Z/n

Explanation: For a multi conductor folded dipole with n conductors, the impedance is n2Z.
Where value of radiation resistance Z depends on the length of the dipole used.

9. Which of the following causes the shortening effect on multi conductor folded dipole?
a) Only thickness of conductors
b) Space between conductors
c) Radiation resistance of the dipole

Explanation: The shortening effect on the multi conductors depends on the thickness of the conductor whereas in wires it depends on the length and the frequency of operation.

10. On which of the following factors does the overall impedance of the unequal conductor folded dipole depends?
a) Only thickness of conductors
b) Space between conductors
c) Radiation resistance of the dipole

Explanation: If the radii of two conductors are r1 (feed arm), r2 (non feed arm) and separated by a distance, then the impedance transformation for folded dipole is given by
$$Z = Z’\left(1+\frac{log⁡(\frac{a}{r1})}{log⁡(\frac{a}{r2})}\right)^2$$ and Z’ is the radiation resistance of the dipole used (which depends on the length of the dipole).
So the overall impedance depends on radii, radiation resistance of the dipole and space between conductors.

Sanfoundry Global Education & Learning Series – Antennas.

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