EC-602 Antenna and Wave Propagation - May 2022 Question Paper

Under each question, How to answer lists the points an answer should cover, outlined by CampusPrep from the syllabus. Check the details against your textbook.

1. 7 Marks
   aDerive the relation for magnetic and electric field components of an alternating current element.
   How to answer

   • Define alternating current element / Hertzian dipole assumptions
   • Derive magnetic vector potential and fields using Maxwell equations
   • Give $H_\phi$, $E_\theta$, $E_r$ components with near and far field terms
   • State far-field approximation and radiation characteristics
2. 7 Marks
   bDerive an expression for the power radiated by Quarter Wave Monopole.
   How to answer

   • Define quarter-wave monopole over ground plane and image concept
   • Write current distribution and far fields
   • Integrate Poynting vector over hemisphere for radiated power
   • Give final expression for radiated power and radiation resistance
3. 7 Marks
   aWhat are the different directional characteristics of dipole antennas?
   How to answer

   • Define radiation pattern, beamwidth, directivity of dipole
   • Explain variation with dipole length: short, half-wave, full-wave
   • Describe E-plane and H-plane directional characteristics
   • Sketch typical patterns
4. 7 Marks
   bExplain Travelling wave antennas in detail.
   How to answer

   • Define travelling wave antenna and non-resonant operation
   • Explain structure: long wire, V, rhombic with terminated end
   • Describe current distribution and directional radiation
   • Give advantages, applications and diagram
5. 7 Marks
   aWhat do you mean by horn antenna? While measuring the gain of a horn antenna the gain oscillator is set for 9 GHz frequency and the attenuation inserted was found to be 9.8 dB. Calculate the gain of the horn, the distance between two horn is 35 cm.
   How to answer

   • Define horn antenna and its types
   • Explain gain measurement by two-horn method formula
   • Substitute $f=9\,GHz$, attenuation $9.8\,dB$, $r=35\,cm$ to compute wavelength and gain
   • State final gain in dB
6. 7 Marks
   bWrite short notes on:

   1. i)Lens antenna
   2. ii)Folded dipole antenna
   How to answer

   • Define lens antenna: principle of focussing
   • Give types and applications
   • Define folded dipole: structure and impedance multiplication
   • State advantages and uses
7. 7 Marks
   aIf the array factor of a line array has zeros at $\Phi = 90^{\circ}$, $180^{\circ}$, $270^{\circ}$ and the elements are spaced at UA. Design the array.
   How to answer

   • Write array factor for linear array and null condition
   • Use given nulls at $\Phi=90^\circ,180^\circ,270^\circ$ to find progressive phase and N
   • Determine spacing UA and excitation
   • State final array design parameters
8. 7 Marks
   bWrite a detailed description and requirements of Planer arrays.
   How to answer

   • Define planar array geometry
   • Explain requirements: uniform excitation, spacing, phasing
   • Describe beam steering and grating lobe control
   • Give applications
9. 7 Marks
   aWith a neat diagram explain the important features of different types of space wave propagation of electromagnetic waves over long distances even beyond the horizon.
   How to answer

   • Define space wave propagation: direct and ground-reflected waves
   • Explain line-of-sight, beyond horizon via tropospheric effects
   • Draw neat diagram showing transmitter, receiver, direct and reflected rays
   • List features: frequency range, coverage, fading
10. 7 Marks
    bObtain the expression of radius of curvature of ray path in terms of rate of change of permittivity with height.
    How to answer

    • State Snell's law in troposphere with varying permittivity
    • Derive differential ray path curvature relation
    • Express radius of curvature in terms of $d\epsilon/dh$
    • Give final expression and interpretation
11. 7 Marks
    aDiscuss the significance of

    1. i)Retarded potential
    2. ii)Radiation resistance
    How to answer

    • Define retarded potential with time-delay concept
    • Explain significance in radiation from time-varying sources
    • Define radiation resistance and its physical meaning
    • Relate radiation resistance to radiated power and efficiency
12. 7 Marks
    bWrite a short note on effect of earth on vertical patterns.
    How to answer

    • Explain image effect of earth on vertical antenna
    • Describe change in vertical radiation pattern and nulls
    • Discuss ground conductivity and reflection factor
    • Summarize effect on gain and coverage
13. 7 Marks
    aWhat is a microstrip antenna? What are different advantages and disadvantages?
    How to answer

    • Define microstrip / patch antenna structure
    • List advantages: low profile, light weight, easy fabrication
    • List disadvantages: narrow bandwidth, low gain, surface waves
    • Give applications
14. 7 Marks
    bExplain feeding structures of antennas.
    How to answer

    • Define antenna feeding and impedance matching need
    • Explain coaxial, microstrip line, aperture and proximity feeds
    • Compare feeding methods
    • State selection criteria
15. 14 Marks
    Define the following terms:

    1. i)V antenna
    2. ii)Sky wave propagation
    How to answer

    • Define V antenna structure and operation
    • Define sky wave propagation via ionosphere
    • Define lens antenna focussing principle
    • Define far-field approximation condition