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Correct option is (a) Axial mode

Explanation: In Axial mode of radiation, the radiation is in end-fire direction along the HELICAL axis. In Axial mode of radiation, the dimensions of antenna are APPROXIMATELY EQUAL to the wavelength and spacing space of λ/4.Axial mode is ALSO known as beam mode or end-fire mode. In normal mode, the radiation is PERPENDICULAR to axis.

Right answer is (B) 0

Easiest explanation: C is the circumference and L is the length, s is the spacing between turns.

When pitch angle α=0, the SEPARATION BECOMES zero and length will be equal to circumference of the loop. Hence it acts as a loop antenna.

Right answer is (a) Rumsey’s principle

Explanation: Rumsey’s principle is used in the frequency INDEPENDENT antennas states that the impedance & pattern of antenna is frequency independent if antennasize is specified in terms of angle. Fabry perot is used with optical WAVES where RAYS are passed only when they are in resonance. Brewster law gives the RELATION to MAXIMUM polarization of light.

The CORRECT ANSWER is (c) \(L < \frac{λ}{2} \)

The EXPLANATION is: 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. \(L < \frac{λ}{2}. \)

The correct CHOICE is (c) Inactive stop region

To explain I WOULD say: 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.

The correct answer is (b) Active region

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.

The correct answer is (a) LPDA

Explanation: LPDA means LOG periodic Dipole Array antenna. It’s all characteristics such as impedance, radiation pattern are FREQUENCY independent. So it is also called as Frequency independent antenna.

Right answer is (a) The dimensions of the antenna are SMALL compared to the WAVELENGTH

To elaborate: The normal mode of radiation DEPENDS on the size of the antenna. Its critical dependency on dimensions of antenna which has to be less than the wavelength is difficult and so it CAUSES for narrow bandwidth and LOW radiation efficiency. Radiation is normal to the direction of axis.

The correct CHOICE is (a) Normal MODE

Explanation: In normal mode, the RADIATION is perpendicular to axis. It is also known as perpendicular mode. In this the antenna DIMENSIONS are smaller COMPARED to the wavelength. Axial mode is also known as beam mode or end-fire mode. In Axial mode of radiation, the radiation is in end-fire direction along the helical axis.

The correct answer is (C) The included angle varies as the length of the dipole changes from the apex of feed line

The EXPLANATION is: 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.

Correct ANSWER is (a) \(\frac{L_N}{L_{N+1}} =τ\)

The best 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 \(\frac{L_N}{L_{N+1}} =τ. \)

The correct answer is (B) False

Best explanation: LOG periodic antenna is frequency independent. The GEOMETRICAL structure of the antenna changes according to the wavelength. It is ALSO called as Frequency Independent antenna. Its electrical PERFORMANCE is dependent on logarithmic of frequency only.

Correct CHOICE is (a) Normal MODE

The best explanation: In normal mode of radiation, the radiation is broadside direction. In AXIAL mode of radiation, it is in end-fire direction. Axial mode is also known as Beam mode.

Correct choice is (b) Resistive

Explanation: The DIFFERENT regions of operation in the LPDA offer different KIND of reactance. In Inactive transmission line regionit OFFERS Capacitive IMPEDANCE, in active region it offers Resistive Impedance and Inactive stop region it offers Inductive impedance.

Correct option is (a) Normal mode

Explanation: The radiation pattern of a helical antenna is a COMBINATION of small dipole and loop antenna. In normal mode of radiation, it provides NARROW BANDWIDTH and low radiation efficiency. AXIAL mode is ALSO known as beam mode or end-fire mode.

The correct option is (a) \(\frac{S_N}{S_{N+1}} = τ\)

Easiest 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 \(\frac{S_N}{S_{N+1}} = τ. \)

The correct option is (d) Variable physical size

Explanation: Rumsey’s principle is used for the frequency independent antenna. A true frequency independent antenna MUST have a FIXED physical size and OPERATES on instantaneous basics over a WIDE bandwidth at a CONSTANT impedance, pattern.

The correct CHOICE is (b) False

The explanation: The self complementary antennas have constant impedance which is half of their intrinsic impedance at all FREQUENCIES. These have a metal AREA congruent to OPEN area. Impedance of self-complementary antenna = Zo/2.

Right choice is (a) 100

The best explanation: DIRECTIVITY of helical ANTENNA D = 12CλnSλ

Pitch angle \(α=TAN^{-1}⁡\frac{S_λ}{C_λ}\)

⇨ Sλ=Cλ tan α=1*0.1=0.1

D = 12CλnSλ

120=12×1×n×0.1

n=100 turns