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This set of Antennas Multiple Choice Questions & Answers (MCQs) focuses on “Radiation Pattern”.

1. Units of radiation intensity is _______
a) Watts/unit Solid angle
b) Watts/m2
c) Watts- m2
d) Watts

Explanation: Radiation intensity is defined as the power radiated form an antenna per unit solid angle. So its units are Watts/Steradian. Steradian is the unit for solid angle.

2. The graphical representation of the radiation properties of the antenna as a function of space coordinates is called Radiation pattern.
a) True
b) False

Explanation: The graphical representation of the radiation properties of the antenna as a function of space coordinates is called Radiation pattern. It is also known as antenna pattern. A radiation property includes power flux density, directivity, and radiation intensity.

3. What is the total power radiated in Watts for the power density $$w_r=\frac{4sin\theta}{3r^2}a_r W/m^2$$?
a) 4π2
b) 8π2/3
c) 4π2/3
d) 2π2/3

Explanation: Total power radiated $$P_{rad}= ∯ w_r.a_n\overline{d}l$$
$$=\iint_{\theta = 0}^{\pi} w_r.r^2 sin\theta d\theta d\emptyset$$
$$=\iint_{\theta = 0}^π\frac{4sin\theta}{3r^2}r^2sin\theta d\theta d \emptyset$$
$$=\iint_{\theta = 0}^π \frac{4}{3}sin^2\theta d\theta d\emptyset=\iint_{\theta=0}^π\frac{4}{3}(\frac{1-cos2\theta}{2})d\theta d\emptyset$$
$$=\frac{4}{3}(\frac{1}{2})(π)(2π)=\frac{4}{3}$$ π2.
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4. Which of the following pattern varies with square of magnitude of field?
a) Power Pattern
b) Electric Field Pattern
c) Current distribution
d) Array Factor

Explanation: Power pattern varies with square of magnitude of field. The average power =$$\frac{\mid \overline{E}\mid^2}{2\eta}$$. It is defined as the trace of received power at a constant radius.

5. The radiation lobe containing the direction of maximum radiation is called as _____
a) Major lobe
b) Minor lobe
c) Side lobe
d) Back lobe

Explanation: Major lobe contains the maximum radiated power. Sometimes depending on our requirement there can be more than 2 major lobes.
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6. Fresnel zone is also called as ____
a) Near Field
b) Far Field
c) Electrostatic Field
d) Reactive Field

Explanation: Near Field is called Fresnel Field. Far field is called Fraunhofer zone. Near field varies inversely with r2. Electrostatic field varies inversely with r3.

7. If FNBW is 6°, then resolution is ____
a) 12°
b) 3°
c) 2°
d) 6°

Explanation: Resolution is half of the first null beam width. $$R=\frac{FNBW}{2}=\frac{6°}{2}=3°.$$

8. For a center fed short antenna, current distribution is _____ at center and ____ at ends.
a) Low, high
b) High, high
c) Low, low
d) High, low

Explanation: The current distribution follows a triangular pattern. At the center it is maximum and nearly zero at ends. Amount of power radiates will depend on the wavelength λ. For vertical antennas, with wavelength n$$\frac{\lambda}{2}$$ the current distribution at center is high.

9. Which pattern represents a plot with magnitude of field strength Vs θ at a constant φ?
a) E-plane pattern
b) H-plane pattern
c) Horizontal pattern
d) Power pattern

Explanation: Varying θ at a constant φ represents a vertical plot against the field strength. So this pattern is called E-plane pattern. H-plane or horizontal pattern are plotted with magnitude of field strength Vs φ at a constant θ. Power pattern is plotted with square of the magnitude of field strength.

10. The portion of the near field immediate to the surrounding the antenna is called as _____
a) Reactive near-field
c) Fraunhofer zone
d) Far field

Explanation: The portion of the near field immediate to the surrounding the antenna is called Reactive near-field. The boundary of this region exists at a distance of R < 0.62√(D3/λ) where D is the largest dimension of the antenna. Radiating near field lies between reactive near field and far field. Far field is also known as Fraunhofer region.

11. The region of the field that angular field distribution is independent of the distance from the antenna is called as _______
a) Reactive near-field
c) Fresnel zone
d) Far field

Explanation: The region of the field that angular distribution is independent of the distance from the antenna is called far field. This region is present at d distance greater than 2D2/λ. Ideally the outer boundary is taken at infinity.

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