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Right OPTION is (a) True

The best explanation: In Elliptical polarization, if the amplitude is made equal, then it becomes a circular polarization. If the PHASE difference of the two linear components is ZERO or nπ then it is becomes a linear polarization. Therefore linear and circular polarization is a SPECIAL case of elliptical polarization.

Correct answer is (b) Ex≠Ey, and ∅=π/2

Explanation: The LOCUS traced by the extremity of the time-varying field vector at a fixed OBSERVATIONAL point is CALLED polarization. In elliptical polarization, the ELECTRIC field COMPONENTS are perpendicular to each other and have unequal magnitude.

Ex≠Ey,and ∅=π/2

The CORRECT choice is (a) polarization

The explanation is: The locus traced by the extremity of the time-varying field vector at a fixed OBSERVATIONAL point is CALLED polarization. GAIN is the OUTPUT to input power ratio. Directivity is the amount of power radiated in the desired direction.

Right option is (C) It has a λ/2 sleeve

The explanation is: Sleeve BALUN has a λ/4 sleeve which is shorted at BASE electrically and it PROVIDES infinite impedance at the top.

Right choice is (a) Lens Law

To elaborate: Lens law GIVES only the REASON for the negative SIGN in the Faradays law of induction

emf=\(-\FRAC{\partial \PHI}{\partial t}\)

The minus sign indicates the direction of induced current.

The correct option is (a) True

Best explanation: POLARIZATION loss factor describes the amount of power loss due to polarization MISMATCH at the receiving antenna from INCIDENT wave. The polarization loss factor due to mismatch if the two linear polarized ANTENNAS are rotated by an angle ∅ is given by PLF = cos^2∅.

Correct option is (b) Constant

For explanation: Hertzian dipole is a short LINEAR ANTENNA which carries a constant current throughout its length while radiating. It consists of TWO equal and OPPOSITE charges separated by a very short DISTANCE. It is infinitesimal current element.

Correct answer is (a) HIGH, low

The best EXPLANATION: SINCE Balun have to minimize the COMMON mode currents it should have High impedance.

For differential mode currents it must have low impedance.

Correct answer is (a) Power loss due to mismatch

To ELABORATE: The polarization loss FACTOR DESCRIBES the power loss due to polarization mismatch. The polarization loss factor due to mismatch if the two linear polarized antennas are rotated by an angle ∅ is given by PLF =cos^2∅.

Correct choice is (b) Faradays LAW

The explanation: Faradays law states that emf GENERATED around a LOOP of wire in magnetic field is proportional to the rate of change of time-varying magnetic field through the loop.

Amperes law gives ∇×H=J

Lens law gives only the reason for the negative SIGN in the Faradays law of induction.

Gauss’s law states that the net flux of an electricfield in a CLOSED surface is directly proportional to the enclosed electric charge.

The correct CHOICE is (c) cos^2∅

Explanation: The POLARIZATION loss factor describes the POWER loss due to polarization MISMATCH. The polarization loss factor due to mismatch if the two linear polarized antennas are rotated by an angle ∅ is given by PLF =cos^2∅.

The CORRECT CHOICE is (B) -3dB

For explanation: The polarization loss factor due to mismatch if the two linear polarized ANTENNAS are ROTATED by an angle ∅ is given by PLF = cos^2∅.

⇨ PLF = cos^2∅=cos^2 45=0.5=-3dB.

The correct answer is (b) PLF=0

For explanation I would SAY: Polarization loss FACTOR DESCRIBES the power loss. When PLF=0=∞ dB, the RECEIVER antenna doesn’t receive any INCIDENT power so there will be a complete mismatch.

Correct option is (b) False

To EXPLAIN I would SAY: A 1:1 BALUN doesn’t provide any impedance transformation. Some Baluns provide impedance transformation like 1: 4 or 9:1.

The correct OPTION is (a) True

Easiest explanation: Since the current distribution at the center is maximum and minimum at ends, there is no UNIFORM distribution of current along length. But Hertzian DIPOLE is derived by ASSUMING a uniform current distribution along length and having INFINITESIMAL length. So that is reason why we don’t use Hertzian dipole practically.

The correct choice is (c) 4.38m

The explanation is: The radiation RESISTANCE of a monopole is 1/8 times the CURRENT element.

\(R_{rad}=10\pi^2 (l/\lambda)^2\)

For a monopole height h= l/2 => l= 2H

\(R_{rad}=10\pi^2(\frac{2h}{\lambda})^2=40\pi^2 (\frac{hf}{c})^2=40\pi^2 (\frac{1×100×10^6}{3×10^{10} })^2=4.38m\Omega\)

Right choice is (a) 1/8

Easiest explanation: The radiation resistance of monopole is ½ times the short dipole. But the radiation resistance of short dipole is ¼ time the current element.

\(R_{RAD \,mono}=\frac{1}{2}×\frac{1}{4}×80\pi^2(\frac{l}{\lambda})^2=\frac{1}{8}×80\pi^2(\frac{l}{\lambda})^2=10\pi^2 (\frac{l}{\lambda})^2=\frac{R_{rad \,Herztian}}{8}\)

The radiation resistance of monopole is 1/8 times the current element.

Right choice is (a) True

The best I can explain: TYPE II Balun has 2 Type I Baluns in SERIES PROVIDING more bandwidth and LOAD impedances at all frequencies. Type -1 Balun has a λ/4 sleeve which is shorted at base electrically.

Correct option is (c) equal, opposite

The explanation is: A Hertzian dipole consists of two equal and opposite CHARGES separated by a very short DISTANCE. It is infinitesimal current element. It is a short linear antenna which carries a CONSTANT current throughout its LENGTH while radiating.

Correct choice is (d) ∇.B=0

For explanation I would SAY: Gauss law for magnetic field states that the net FLUX out of any closed surface is zero.

∇.B=0

This is satisfied only when two different poles of magnet exist. So this Maxwell EQUATION proves for the NONEXISTENCE of the isolated magnetic charge.

Faradays Law: ∇×E=\(-\FRAC{\partial B}{\partial t}\)

Amperes Law: ∇×H=J

Gauss Law for electric field: ∇.D=ρv

The CORRECT choice is (a) 9R

The best explanation: A 1:9 BALUN REPRESENTS that the balanced IMPEDANCE is 9 times the unbalanced impedance.

⇨ Balanced impedance =9×R=9R

Right ANSWER is (a) POLARIZATION MISMATCH

Easiest EXPLANATION: The polarization of received antenna is not same as incident WAVE polarization is termed as Polarization mismatch. The polarization loss factor describes the power loss due to polarization mismatch. PLF =cos^2∅.

The CORRECT choice is (a) Current Balun

To elaborate: A current Balun offers better balance and can tolerate load IMPEDANCES and balance variations better compared to VOLTAGE Balun. In a current Balun the output terminal voltage can be of any value to make the CURRENTS equal in the feed line.

The correct option is (d) ∇.D=ρv

For explanation: Gauss’s LAW for electric FIELD states that the NET flux of an electricfield in a closed SURFACE is directly PROPORTIONAL to the enclosed electric charge. ∇.D=ρv

This Maxwell equation is one of the equation used to determine the boundary conditions.

Correct CHOICE is (b) Linear

Explanation: The linear polarization takes place in the monopole DIPOLE. In the Dipole also a linear polarization takes place. Parabolic reflectors take the polarization of the feed. In HELICAL, CIRCULAR loop ANTENNAS we can find the circular polarization.

The correct option is (a) ∇.B=0

The best I can explain: Gauss law for magnetic FIELD states that the net flux out of any CLOSED SURFACE is zero.

∇.B=0

This Maxwell equation is one of the equation used to DETERMINE the BOUNDARY conditions.

Right CHOICE is (a) 4

To explain I would say: A BALUN can be viewed as a transformer. \(\FRAC{Z_{unbal}}{Z_{BAL}} = (turns \,ratio)^2=(\frac{1}{2})^2=\frac{1}{4} \)

⇨ Zbal = 4Zunbal

So the balanced impedance is four TIMES the unbalanced impedance.

Correct option is (c) Tapered Balun

For explanation I would say: Tapered Balun changes the shape of the unbalanced transmission line to that of a balanced transmission line. Sleeve Balun uses a λ/4 sleeve which is shorted at BASE ELECTRICALLY and it PROVIDES infinite IMPEDANCE at the top. Infinite Balun uses the current flowing OUTSIDE the conductor as a part of antenna.

Correct option is (a) CURRENT distribution

For EXPLANATION I WOULD SAY: A Balun is a DEVICE which connects a balanced two –conductor line to an unbalanced coaxial line. It eliminates field mismatch. It forces the current at the outer side of outer conductor to be zero. This is called current choke.

The correct choice is (a) \(\frac{\eta_0 w^2 dl^2}{6\pi c^2}\)

To explain: Radiation resistance of a HERTZIAN dipole is \(R_{RAD} = 80\pi^2(\frac{l}{\LAMBDA})^2\)

By simplifying the options GIVEN above,

\(\frac{\eta_0 w^2 dl^2}{6\pi c^2} = \frac{120\pi(2\pi/\lambda)^2 dl^2}{6\pi} = 80\pi^2(\frac{l}{\lambda})^2\)

Right option is (b) 0.9113μm

The EXPLANATION: The SKIN depth is given by \(δ = \SQRT{\FRAC{1}{\PI fμσ}}\)

Given f=5GHz

Conductivity σ= 6.1×10^7 s/m

And μr = 1 =>μ=4π ×10^-7

⇨ \(δ = \sqrt{\frac{1}{\pi fμσ}}=0.9113\mu m.\)

Right option is (a) PLF=1

For EXPLANATION: Polarization LOSS FACTOR describes the power loss. When PLF = 1 = 0dB indicates total power incident is received by the antenna. Therefore the condition for the no power loss is PLF=1

Right option is (a) Ex=Ey, and ∅=π/2

The best EXPLANATION: The locus traced by the extremity of the time-varying FIELD vector at a fixed observational point is called polarization. Circular polarization has ELECTRIC field COMPONENTS are perpendicular to each other and have EQUAL magnitude. Ex=Ey, and ∅=π/2.

Correct CHOICE is (d) Type – 3

To explain: Type – 3 Baluns has a sliding SHORT circuit bar for frequency ADJUSTMENT. Sleeve BALUN or Type -1 Balun has a λ/4 sleeve which is shorted at base ELECTRICALLY.

Right choice is (a) 0≤PLF≤1

The BEST explanation: The polarization loss factor DUE to mismatch if the two linear polarized antennas are ROTATED by an angle ∅ is given by PLF = cos^2∅.

⇨ Max value of PLF = 1

⇨ Min value of PLF = 0

⇨ 0≤PLF≤1

The correct OPTION is (a) τ=\(TAN^{-1}(\FRAC{a_{vertical}}{a_{horizontal}})\)

For explanation: The two PROPERTIES of ellipse that relates to the polarization are — eccentricity and tilt or inclination ANGLE with respect to horizontal. Tilt angle of the elliptic polarization is given by

τ=\(tan^{-1}(\frac{a_{vertical}}{a_{horizontal}})\)

Right CHOICE is (a) 180°

To EXPLAIN I would say: A BALUN can be viewed as a three port device, with MATCHED input and a differential output. The differential outputs are equal and opposite. So, they are 1800 out of phase with respect to each other.

Right choice is (a) Zero

To explain I would SAY: When a coaxial cable is connected to a half wave dipole, the current distribution along the OUTER SIDE of the outer conductor may also present. It results in loss and field MISMATCH. So a Balun is used to make the current at the outer side of the outer conductor zero. Current distribution is present at the INNER side of the outer conductor.

Correct CHOICE is (a) 25

Best explanation: The radiation resistance of the short dipole is ¼ times the radiation resistance of a CURRENT element. So 100/4= 25Ω.

Correct choice is (a) 0.75

To EXPLAIN I would say: The polarization loss FACTOR due to MISMATCH if the two linear polarized antennas are ROTATED by an angle ∅ is given by PLF = cos^2∅

⇨ PLF = cos^230=\(\frac{3}{4}=0.75\)