Antennas Questions and Answers – Frequency Independent Antenna – Working of LPDA

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This set of Antennas Questions and Answers for Freshers focuses on “Frequency Independent Antenna – Working of LPDA”.

1. Which of the following is the condition for the Log periodic antenna to be in active region?
a) \(L = \frac{λ}{2} \)
b) \(L > \frac{λ}{2} \)
c) \(L < \frac{λ}{2} \)
d) \(L = \frac{λ}{4} \)
View Answer

Answer: a
Explanation: Based on the lengths of the dipoles in LPDA, operation region is classified into three types:
Inactive transmission line region \(L < \frac{λ}{2} \)
Active region \(L=\frac{λ}{2} \)
Inactive stop region \(L > \frac{λ}{2}. \)
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2. Which of the following is the condition for the Log periodic antenna to be inactive stop region?
a) \(L=\frac{λ}{2} \)
b) \(L > \frac{λ}{2} \)
c) \(L < \frac{λ}{2} \)
d) \(L = \frac{λ}{4} \)
View Answer

Answer: b
Explanation: Based on the lengths of the dipoles in LPDA, operation region is classified into three types:
Inactive transmission line region, Active region and Inactive stop region. The region below \(L < \frac{λ}{2} \) belongs to Inactive transmission region. The region above \(L > \frac{λ}{2} \) is Inactive stop region.

3. Which of the following is the condition for the Log periodic antenna to be inactive transmission line region?
a) \(L=\frac{λ}{2} \)
b) \(L > \frac{λ}{2} \)
c) \(L < \frac{λ}{2} \)
d) \(L = \frac{λ}{4} \)
View Answer

Answer: c
Explanation: The LPDA has dipoles of varying length along the axis. The dipole lengths of the LPDA less than half the wavelength belongs to the Inactive transmission line region. \(L < \frac{λ}{2}. \)
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4. The dipoles in the inactive transmission region offer ________ impedance.
a) Capacitive
b) Resistive
c) Inductive
d) Characteristic
View Answer

Answer: a
Explanation: Depending on the length of the dipoles, in different regions they offer different resistances.
In Inactive transmission line region \(L < \frac{λ}{2}\) offers Capacitive Impedance
Active region \(L=\frac{λ}{2} \) offers Resistive Impedance
Inactive stop region \(L > \frac{λ}{2} \) offers Inductive impedance.

5. The dipoles in the active region offer ________ impedance.
a) Capacitive
b) Resistive
c) Inductive
d) Characteristic
View Answer

Answer: b
Explanation: The different regions of operation in the LPDA offer different kind of reactance. In Inactive transmission line region it offers Capacitive Impedance, in active region it offers Resistive Impedance and Inactive stop region it offers Inductive impedance.
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6. The dipoles in the inactive stop region offer ________ impedance.
a) Capacitive
b) Resistive
c) Inductive
d) Characteristic
View Answer

Answer: c
Explanation: The varying length of the dipoles in LPDA forms different regions and they offer different resistances. The Inactive transmission line region at \(L < \frac{λ}{2}\) offers Capacitive Impedance, Active region at \(L=\frac{λ}{2} \) offers Resistive Impedance and Inactive stop region \(L > \frac{λ}{2} \) offers Inductive impedance.

7. In which of the following region in LPDA, the current leads the base voltage?
a) Inactive transmission line region
b) Active region
c) Inactive stop region
d) Reflective region
View Answer

Answer: a
Explanation: In LPDA, the length of dipole \(L < \frac{λ}{2}\) comes under inactive transmission region. These region dipoles offer capacitive impedance. So the current leads the base voltage in the inactive transmission line region. Active region \(L=\frac{λ}{2} \) offers Resistive Impedance and Inactive stop region \(L > \frac{λ}{2} \) offers Inductive impedance.
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8. In which of the following region of the log periodic array, maximum radiation takes place?
a) Inactive transmission line region
b) Active region
c) Inactive stop region
d) Reflective region
View Answer

Answer: b
Explanation: In LPDA, the length of dipole \(L=\frac{λ}{2} \) comes under active region. These region dipoles offer resistive impedance. Here currents are large and are in phase with the base voltage. Inactive stop region is also called as reflective region.In Inactive transmission line region \(L < \frac{λ}{2}\) offers Capacitive Impedance and Inactive stop region \(L > \frac{λ}{2} \) offers Inductive impedance.

9. Which of the following region is also known as reflective region in LPDA?
a) Inactive transmission line region
b) Active region
c) Inactive stop region
d) Log periodic array
View Answer

Answer: c
Explanation: Inactive stop region \(L > \frac{λ}{2} \) offers Inductive impedance. Any small incident wave gets reflected easily by large inductive impedance hence this region is also known as reflective region.
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10. Reflective region in LPDA offers the inductive impedance.
a) True
b) False
View Answer

Answer: a
Explanation: The Reflective region is also known as the Inactive stop region. The Inactive stop region \(L > \frac{λ}{2}\) offers Inductive impedance. This region is called reflective region because any small incident wave gets reflected easily by large inductive impedance and thus offers inductive impedance.

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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