EC-602 Antenna and Wave Propagation - Dec 2024 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
   aDescribe the concept of retarded potential and its significance in antenna theory. How does it differ from static potential?
   How to answer

   • Define retarded potentials with time-delay $R/c$ expression
   • Explain finite propagation velocity and causality
   • Significance for radiation fields and antenna analysis
   • Difference from static instantaneous potentials
2. 7 Marks
   bExplain the near-field and far-field regions of an antenna. What are the primary differences between them in terms of field components?
   How to answer

   • Define near-field (reactive, Fresnel) and far-field (Fraunhofer) regions
   • Give distance criteria and field decay with distance
   • Compare field components: E, H phase and radiation vs stored energy
   • Diagram of regions around antenna
3. 7 Marks
   aDiscuss the power radiated by an oscillating electric dipole. How is this power dependent on the frequency and current distribution?
   How to answer

   • Expression for fields of oscillating electric dipole / Hertzian dipole
   • Poynting vector integration for total radiated power
   • Dependence $P \propto f^2$ or $f^4$ and $I_0$, $dl/\lambda$ relation
   • Effect of current distribution on radiation
4. 7 Marks
   bDefine the following:

   1. i)Directivity and Radiation Pattern
   2. ii)Antenna arrays
   How to answer

   • Define directivity as ratio of max to average radiation intensity
   • Define radiation pattern with lobes and types
   • Define antenna array and need for arrays
   • Give examples / significance
5. 7 Marks
   aDescribe the significance of antenna gain. If an antenna has a gain of 20 dB. Calculate its effective area at a frequency of 1 GHz.
   How to answer

   • Define antenna gain vs directivity and efficiency
   • Relation $G = 4\pi A_e/\lambda^2$
   • Convert 20 dB to linear ratio 100
   • Calculate $A_e$ at 1 GHz ($\lambda=0.3$ m)
6. 7 Marks
   bExplain the directional properties of dipole antennas.
   How to answer

   • Radiation pattern of dipole vs length ($\lambda/2$, short dipole)
   • Omnidirectional in H-plane, figure-of-eight in E-plane
   • Effect of length on directivity and nulls
   • Polarization and practical implications
7. 7 Marks
   aExplain the construction and operational principle of a log-periodic antenna. Discuss its applications in telecommunications.
   How to answer

   • Structure: tapered dipole lengths with constant ratio tau and spacing sigma
   • Active region principle and log-periodic frequency independence
   • Feed and phasing mechanism
   • Telecommunication applications e.g. TV, broadband
8. 7 Marks
   bExplain the construction and function of a Yagi-Uda antenna. Why is it widely used for TV reception?
   How to answer

   • Components: driven element, reflector, directors
   • Parasitic excitation and end-fire operation
   • Gain, directivity and front-to-back ratio
   • Reason for TV reception: high gain, low cost, directional
9. 7 Marks
   aDiscuss the construction and radiation mechanism of a microstrip antenna. Explain one advantage and one limitation of microstrip antennas.
   How to answer

   • Construction: patch, substrate, ground plane, feed
   • Radiation via fringing fields at edges
   • One advantage e.g. low profile, low cost
   • One limitation e.g. narrow bandwidth, low efficiency
10. 7 Marks
    bHow does aperture blockage affect the performance of reflector antennas? Explain.
    How to answer

    • Define aperture blockage by feed and supports
    • Effect on gain loss, sidelobe increase
    • Effect on efficiency and pattern distortion
    • Mitigation e.g. offset feed
11. 7 Marks
    aCalculate the MUF for a signal with a critical frequency of 6 MHz and an angle of incidence of $45^{\circ}$.
    How to answer

    • State secant law $MUF = f_c \sec \theta_i$
    • Substitute $f_c=6$ MHz, $\theta_i=45^\circ$
    • Compute $MUF \approx 8.49$ MHz
    • Mention significance for oblique incidence
12. 7 Marks
    bDescribe the phenomenon of tropospheric scattering and how it affects radio wave propagation?
    How to answer

    • Define tropospheric scattering / troposcatter
    • Mechanism: inhomogeneities and turbulence
    • Effect: beyond-horizon propagation, fading
    • Use for long-distance UHF/SHF links
13. 7 Marks
    aDiscuss the effect of frequency and terrain on ground wave propagation. Provide a practical example.
    How to answer

    • Ground wave attenuation vs frequency and conductivity
    • Terrain effect: roughness, obstacles, diffraction
    • Practical example e.g. AM broadcast coverage
    • Summary of low-frequency suitability
14. 7 Marks
    bDefine MUF (Maximum Usable Frequency), LUF (Lowest Usable Frequency), and skip distance in sky wave propagation. Explain their relevance to long-distance communication.
    How to answer

    • Define MUF, LUF and skip distance
    • Ionospheric reflection and usable frequency window
    • Relevance for choosing operating frequency
    • Importance for long-distance sky-wave communication
15. 14 Marks
    Write short notes on (any two) :

    1. a)Helical antenna
    2. b)Horn antennas
    3. c)Rhombic antenna
    How to answer

    • For each chosen antenna: construction and working
    • Radiation characteristics and modes
    • Applications and advantages
    • Comparison of use cases