# Antennas Questions and Answers – Frequency Independent Antenna – Log Periodic Antenna Introduction

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This set of Antennas Multiple Choice Questions & Answers (MCQs) focuses on “Frequency Independent Antenna – Log Periodic Antenna Introduction”.

1. Frequency range of LPDA is ________
a) 3 MHz to 30 MHz
b) 30 KHz to 30 GHz
c) 30 MHz to 3 GHz
d) 300 KHz to 300GHz

Explanation: Log periodic antenna uses around 30MHz to 3GHz frequency range.
MF – Medium Frequency – 300-3000 KHz
HF – High Frequency – 3-30 MHz
VHF – Very high frequency – 30-300 MHz
UHF – Ultra high frequency – 300MHz to 3GHz
So it uses VHF and UHF.

2. Which of the following band of frequency the LPDA operates?
a) VHF & UHF
b) UHF & MF
c) MF & HF
d) HF & UHF

Explanation: Log periodic antenna uses VHF and UHF band.
MF and UHF – 300 kHz to 3GHz
MF and HF – 300 kHz to 30MHz
HF and UHF – 3MHz to 3GHz
LPDA operates at 30MHz to 3GHz frequency range.

3. In frequency independent antennas, the antennas are defined in terms of _________
a) Angles
b) Wavelengths
c) Range
d) Frequency

Explanation: If the antennas are defined only in terms of angles, then they are frequency independent antennas. Its impedance and radiation pattern are independent of the frequency. Example of frequency independent antennas are log periodic antennas, spiral antennas.

4. The relation between the dipole lengths and the scaling factor τ in LPDA is given by _________
a) $$\frac{L_N}{L_{N+1}} =τ$$
b) $$\frac{L_N}{L_{N+1}} =\frac{1}{τ}$$
c) $$\frac{L_N}{L_{N+2}} =τ$$
d) $$\frac{L_{N+2}}{L_N} =τ$$

Explanation: The electrical properties of the log periodic antenna are repeated periodically in terms of logarithmic frequency. The relation between the antenna dipole adjacent lengths and the scaling factor is given as $$\frac{L_N}{L_{N+1}} =τ.$$

5. Which of the following statement is false?
a) LPDA is a frequency independent antenna
b) In LPDA the lengths of the dipoles increases from the apex of the feed line toward other end
c) The included angle varies as the length of the dipole changes from the apex of feed line
d) The spacing between adjacent dipoles and their lengths are in same ratio

Explanation: The electrical properties of the LPDA are periodically repeated in terms of logarithmic frequency. The relation between the antenna dipole spacing lengths or adjacent lengths and the scaling factor is given as$$\frac{L_N}{L_{N+1}} =\frac{S_N}{S_{N+1}} = τ.$$ LPDA is a frequency independent antenna and the lengths of the dipoles increases from the apex of the feed line toward other end by maintaining constant included angle.

6. The ratio of adjacent spacing of dipoles and its lengths in the LPDA are not equal.
a) True
b) False

Explanation: The ratio of adjacent spacing of dipoles and its lengths in the LPDA are equal. The electrical properties of the log periodic antenna are repeated periodically in terms of logarithmic frequency. The relation between the antenna dipole adjacent lengths, spacing and the scaling factor is given as$$\frac{L_N}{L_{N+1}} =\frac{S_N}{S_{N+1}} =τ.$$

7. The relation between the dipole spacing and the scaling factor τ in LPDA is given by _________
a) $$\frac{S_N}{S_{N+1}} = τ$$
b) $$\frac{S_N}{S_{N+1}} = \frac{1}{τ}$$
c) $$\frac{S_N}{S_{N+2}} = τ$$
d) $$\frac{S_{N+2}}{S_N} = τ$$

Explanation: The electrical properties of the log periodic antenna are repeated periodically in terms of logarithmic frequency. The relation between the antenna dipole adjacent spacing and the scaling factor is given as $$\frac{S_N}{S_{N+1}} = τ.$$

8. Which of the following expression is correct?
a) $$\frac{L_N}{L_{N+1}} = \frac{S_N}{S_{N+1}} = τ$$
b) $$\frac{L_N}{L_{N+1}} = \frac{S_{N+1}}{S_N} = τ$$
c) $$\frac{L_N}{L_{N+1}} = \frac{S_{N+1}}{S_N} = \frac{1}{τ}$$
d) $$\frac{L_N}{L_{N+1}} = \frac{S_N}{S_{N+1}} = \frac{1}{τ}$$

Explanation: The ratio of adjacent spacing of dipoles and its lengths in the LPDA are equal. The electrical properties of the log periodic antenna are repeated periodically in terms of logarithmic frequency. The relation between the antenna dipole adjacent lengths, spacing and the scaling factor is given as $$\frac{L_N}{L_{N+1}} = \frac{S_N}{S_{N+1}} = τ.$$