1. 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
2. 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
3. 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.
4. 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
\(Z = Z’\left(1+\frac{log(\frac{a}{r1})}{log(\frac{a}{r2})}\right)^2.\)
5. 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
\(Z = 73\left(1+\frac{log(\frac{a}{r1})}{log(\frac{a}{r2})}\right)^2\)
6. 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.
7. 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
d) Both the radii and radiation resistance
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.
8. 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
d) Radii, radiation resistance and space between conductors.
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.
9. The directivity of Yagi-Uda antenna is increased by adding ______
a) reflectors
b) driven element
c) directors
d) boom
Explanation: Addition of directors leads to focus the beam in the forward direction. So, directors will increase the gain of antenna. Folded dipole acts like a feed or driven element. Reflectors will increase the directivity of antenna by reflecting all energy towards radiation direction of antenna. Boom is a center rod on which elements are mounted.
10. Directors are used to increase ______ of the Yagi-Uda antenna.
a) Directivity
b) Gain
c) Back lobe
d) Reflection away from the radiation
Explanation: Reflectors will increase the directivity of antenna by reflecting all energy towards radiation direction of antenna. Addition of directors leads to focus the beam in the forward direction. So, directors will increase the gain of antenna.