## Antenna and Wave Propagation - Dec 2015

### Electronics & Telecom Engineering (Semester 6)

TOTAL MARKS: 100

TOTAL TIME: 3 HOURS
(1) Question 1 is compulsory.

(2) Attempt any **four** from the remaining questions.

(3) Assume data wherever required.

(4) Figures to the right indicate full marks.

### Solve any one question from Q1 and Q2

**1 (a)** What is Poynting vector? What is its significance? Derive an expression
for Poynting vector?(6 marks)
**1 (b)** Derive the fundamental equation for free space propagation and explain
its parameter(6 marks)
**1 (c)** A lossless resonant λ/2 dipole antenna with input impedance of 73 Ω is to be connected to a transmission line whose characteristics impedance
is 50Ω. Assuming that the pattern of the antenna is given approximately
by U=Bosin ^{3}θ. Find the overall maximum gain of this antenna.(8 marks)
**2 (a)** State Maxwell's field equation with their significane and derive the wave
equation foe lossless dielectric medium.(6 marks)
**2 (b)** Derive vector potential A for an magnetic current source J.(6 marks)

### Explain the following wireless channel characteristics

**2 (c) (i)** Coherence bandwidth(4 marks)
**2 (c) (ii)** Coherence time(4 marks)

### Solve any one question from Q3 and Q4

**3** Find the following terms for half wave Dipole:

a) Specify the current

b) Vector magnetic potential

c) Far field components of Electric & Magnetic fields

d) radiation density, radiation intensity

e) radiated power, radiation resistance

f) Directivity

g) draws the radiation pattern(18 marks)
**4 (a)** Calculate the radiation resistance of a double turn and an eight turn small circular loop when radius of loop is λ/10 and the medium is free space.
Calculate its efficiency if loss resistance is 25Ω.(6 marks)
**4 (b)** Derive the expression for radiation resistance of Infinitesimaldipole.(6 marks)
**4 (c)** Derive the expression for input impedance of small dipole.(6 marks)

### Write short notes on:

**5 (a) (i)** Pattern Multiplication(4 marks)
**5 (a) (ii)** Binomial Array(4 marks)
**5 (b)** An Endfire array with element spaced at λ/2 and with axes of elements
at right angles to the line of array is required to have directivity of 36. Determine - the array length and the width of major lobe.(8 marks)
**6 (a)** Design a broad side Dolph-Tschebhysheff array of five elements with
half wavelength spacing between elements and with major to minor lobe
ratio to be 19dB. Find the excitation coefficients & array factor.(6 marks)
**6 (b)** Give the comparison of broadside and End fire antenna array.(5 marks)
**6 (c)** Explain planar array. State its advantages and applications.(5 marks)

### Solve any one question from Q7 and Q8

**7 (a)** What is Microstrip patch antenna? Give structure details, radiation pattern,
specification and application of such antenna.(5 marks)
**7 (b)** What is meant by Rhombic Antenna? How it is constructed? Explain
how unidirectional pattern is obtained in properly terminated Rhombic
Antenna.(5 marks)
**7 (c)** Write a short notes on following antennas with respect to structural details,
radiation pattern, features and applications.

i) Hertz antenna

ii) Whip antenna(6 marks)

### Write a short note on the following antennas

**8 (a) (i)** Lens Antenna(4 marks)
**8 (a) (ii)** Resonant Antenna(4 marks)
**8 (a) (iii)** Super - turnstile Antenna(4 marks)
**8 (b)** A paraboloidal reflector antenna with diameter 20m is designed to operate at frequency of 6 GHz and illumination efficiency of 0.54. Calculate the
antenna gain in decibels.(4 marks)