Antennas Questions and Answers – Aperture Antenna – Beamwidths

«
»

This set of Antennas written test Questions & Answers focuses on “Aperture Antenna – Beamwidths”.

1. Half-power Beamwidth is given by ____
a) 70λ/D
b) 70D/λ
c) 35λ/D
d) 35D/λ
View Answer

Answer: a
Explanation: The area the power is radiated is given by Beamwidth. Half power Beamwidth is the area at which the power is radiated 50% of peak power. The half-power beamwidth is given by70λ/D.
advertisement

2. If the antenna dimension is two times the wavelength of the signal then the half power beam width will be _____
a) 35
b) 140
c) 70
d) 280
View Answer

Answer: a
Explanation: The half-power beamwidth is given by70λ/D.
⇨ \(\frac{70\lambda}{D}=\frac{70}{2}=35.\)

3. For a circular aperture the FNBW is ______
a) 140λ/D
b) 70λ/D
c) 140D/λ
d) 70D/λ
View Answer

Answer: a
Explanation: The area the power is radiated is given by Beam-width. The beam-width between the first nulls is the FNBW. For circular aperture the FNBW is given by 140λ/D. The half-power beam width is given by 70λ/D.
advertisement
advertisement

4. If the antenna dimension is two times the wavelength of the signal then the First null beam width will be _____
a) 35
b) 140
c) 70
d) 280
View Answer

Answer: c
Explanation: The first null beam-width is given by 140λ/D.
⇨ \(\frac{140\lambda}{D} = \frac{140}{2}=70.\)

5. For a rectangular aperture of a*b the first null in E-plane occur at _______
a) sin-1⁡(λ/b)
b) sec-1⁡(λ/b)
c) cos-1⁡(λ/a)
d) sin-1⁡(λ/a)
View Answer

Answer: a
Explanation: The area the power is radiated is given by Beam-width. The beam-width between the first nulls is the FNBW. \(\frac{kb}{2}\) sinθ=nπ
⇨ θ= sin-1⁡(nλ/b)
⇨ For first null n=1 θ= sin-1⁡(λ/b).
advertisement

6. The first null beam width in the E-plane of a rectangular aperture of a×b is given by _______________
a) 2sin-1⁡(λ/b)
b) sin-1⁡(λ/a)
c) 2sec-1⁡(λ/b)
d) 2cos-1⁡(λ/a)
View Answer

Answer: a
Explanation: The area the power is radiated is given by Beam-width. The beam-width between the first nulls is the FNBW. \(\frac{kb}{2}\) sinθ=nπ
θ= sin-1\(⁡(\frac{n\lambda}{b})\)
Therefore, the FNBW in E-plane is given by FNBW=2 θ = sin-1⁡\(⁡(\frac{\lambda}{b})\).

7. Larger the size of the aperture, the narrower is the Beam-widths.
a) True
b) False
View Answer

Answer: a
Explanation: The FNBW in E-plane is given by FNBW=2 θ = sin-1⁡\(⁡(\frac{n\lambda}{b})\). As the dimension of the antenna aperture increases, the FNBW will decrease. Thereby, beam-width becomes narrower.
advertisement

8. Half-power Beam width in E-plane for a rectangular aperture antenna of a×b is given by ____
a) 0.886λ/b
b) 0.443λ/b
c) 0.5λ/b
d) λ/b
View Answer

Answer: a
Explanation: By equating the field in E-plane to half power point
\(\frac{sin⁡(0.5kbsin\theta)}{0.5kbsin\theta} = \frac{1}{\sqrt 2} => \theta = arcsin⁡(\frac{0.443
\lambda}{b})\)
Now HPBW = 2 arcsin⁡\((\frac{0.443\lambda}{b})\)≈0.886λ/b.

9. Find the HPBW of the uniform rectangular aperture antenna with 4λ×2λ in the E-plane?
a) 0.443
b) 0.886
c) 0.25
d) 0.5
View Answer

Answer: a
Explanation: HPBW = 2 arcsin⁡\((\frac{0.443\lambda}{b})\)≈0.886λ/b=0.886/2=0.443.
advertisement

10. The value at which the second null occurs in H-plane of rectangular aperture of a*b is given by ____
a) sin-1⁡(2λ/a)
b) sin-1⁡(λ/a)
c) sin-1⁡(a/2λ)
d) sin-1⁡(a/λ)
View Answer

Answer: a
Explanation: The area the power is radiated is given by Beam-width. The beam-width between the first nulls is the FNBW. For H-plane \(\frac{ka}{2}\) sinθ=nπ
⇨ θ= sin-1⁡(nλ/a)
⇨ For null n=2 θ= sin-1⁡(2λ/a).

Sanfoundry Global Education & Learning Series – Antennas.

To practice all written questions on Antennas, here is complete set of 1000+ Multiple Choice Questions and Answers.

Participate in the Sanfoundry Certification contest to get free Certificate of Merit. Join our social networks below and stay updated with latest contests, videos, internships and jobs!

advertisement
advertisement

Leave a Comment

Manish Bhojasia - Founder & CTO at Sanfoundry
Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He is Linux Kernel Developer & SAN Architect and is passionate about competency developments in these areas. He lives in Bangalore and delivers focused training sessions to IT professionals in Linux Kernel, Linux Debugging, Linux Device Drivers, Linux Networking, Linux Storage, Advanced C Programming, SAN Storage Technologies, SCSI Internals & Storage Protocols such as iSCSI & Fiber Channel. Stay connected with him @ LinkedIn | Youtube | Instagram | Facebook | Twitter