# Horn Antenna Questions and Answers – Design – 1

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This set of Antennas Multiple Choice Questions & Answers (MCQs) focuses on “Design – 1”.

1. If the flare angle of the horn increases, then its beam width ______
a) Decreases
b) Increases
c) Depends on aperture of horn
d) Independent of flare angle

Explanation: The beam width of the horn antenna increases as the flare angle increases. The reflections are decreases as the flare angle increases. But at 900, the antenna approximates to an open end waveguide and its gain decreases.

2. Find the width of aperture of the E-plane horn operating at frequency 800MHz with the slant length 5cm?
a) 1.936 cm
b) 19.36 cm
c) 0.194 cm
d) 1.936 m

Explanation: Aperture width $$= \sqrt{2λL}=\sqrt{\frac{2c}{f} L}=\sqrt{\frac{2×3×10^{10}}{800×10^6}×5}=19.36 cm$$

3. Find the aperture width of the H-plane horn operating at frequency 900MHz with the slant length 5cm?
a) 2.236 cm
b) 22.36 cm
c) 0.224 cm
d) 2.236 m

Explanation: Aperture width $$= \sqrt{3λL}=\sqrt{\frac{3c}{f} L}=\sqrt{\frac{3×3×10^{10}}{900×10^6}×5}=22.36 cm$$

4. Find the diameter of the conical horn operating at frequency 900MHz with the slant length 1.5cm?
a) 1.224 cm
b) 12.24 cm
c) 0.122 cm
d) 1.224 m

Explanation: Diameter $$= \sqrt{3λL}=\sqrt{\frac{3c}{f} L}=\sqrt{\frac{3×3×10^10}{900×10^6}×1.5}=12.24 cm$$

5. Find the directivity of a pyramidal horn antenna with E-plane aperture width 10λ and H-plane aperture width 15λ?
a) 30.15dB
b) 30.51dB
c) 3.051dB
d) 35.01dB

Explanation: Directivity $$= 10log_{10}\frac{7.5A_e}{λ^2} = 10log_{10}\frac{7.5×10λ×15λ}{λ^2} =30.51dB$$

6. Find the length of the E-plane horn with aperture 12λ and path travel difference 0.4λ?
a) 3.5 λ
b) 45 λ
c) 54 λ
d) 9 λ

Explanation: Length of the E-plane horn $$ρ =\frac{h^2}{8δ}=\frac{(12λ)^2}{8×0.4λ}=45 λ$$

7. Find the flare angle of the H-plane horn with aperture 12λ and path travel difference 0.4λ?
a) 15.18°
b) 7.09°
c) 30.18°
d) 1.518°

Explanation: Length of the H-plane horn $$ρ =\frac{h^2}{8δ}=\frac{(12λ)^2}{8×0.4λ}=45 λ$$
Flare angle of the H-plane horn = $$2tan^{-1}⁡\frac{h}{2ρ}=2×tan^{-1}⁡\frac{12λ}{2×45λ}=15.18°$$

8. Which of the following is the correct form of design equations of a horn antenna?
a) Length $$ρ=\frac{h^2}{8δ}, flare\, angle=2tan^{-1}⁡\frac{h}{2ρ}$$
b) Length $$ρ=\frac{h^2}{4δ}, flare\, angle=2tan^{-1}⁡\frac{h}{2ρ}$$
c) Length $$ρ=\frac{h^2}{4δ}, flare\, angle=tan^{-1}⁡\frac{h}{2ρ}$$
d) Length $$ρ=\frac{h^2}{8δ}, flare\, angle=tan^{-1}⁡\frac{h}{2ρ}$$

Explanation: Design equations of a horn antenna are:
Length $$ρ=\frac{h^2}{8δ},flare\, angle\, θ=2 tan^{-1}⁡\frac{h}{2ρ}$$ 9. What are the length and the flare angle of the H-plane horn antenna with aperture 10 λ and path difference δ=0.2λ?
a) Length=31.8λ,flare angle=4.15°
b) Length=62.5λ,flare angle=9.14°
c) Length=31.8λ,flare angle=9.14°
d) Length=62.5λ,flare angle=4.15°

Explanation: Length of the H-plane horn $$ρ=\frac{h^2}{8δ}=\frac{(10λ)^2}{8×0.2λ}=62.5λ$$
Flare angle of the H-plane horn $$= 2tan^{-1}⁡\frac{h}{2ρ}=2×tan^{-1}⁡\frac{10λ}{2×62.5λ}=9.14°$$

10. Find the optimum aperture angle for H-plane horn with aperture 12λ and path travel difference 0.4λ?
a) 75.9°
b) 1.59°
c) 7.59°
d) 15.18°

Explanation: Optimum aperture angle of the H-plane horn = $$tan^{-1}⁡\frac{h}{2ρ}=tan^{-1}⁡\frac{12λ}{2×45λ}=7.59°$$ 