EC-702-A Microwave Engineering - Dec 2025 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 expressions for effective dielectric constant and characteristic impedance of a microstrip line.
   How to answer

   • Define microstrip geometry and quasi-TEM assumption
   • Effective dielectric constant formula for W/h ranges
   • Characteristic impedance expressions for narrow and wide strips
   • Effect of substrate permittivity, W/h and frequency
2. 7 Marks
   bExplain the construction and working of a reflex klystron and draw its mode curve.
   How to answer

   • Construction: cavity, repeller, electron gun and coupling
   • Velocity modulation and bunching in repeller space
   • Working and oscillation condition
   • Mode curve: power/frequency vs repeller voltage with modes
3. 7 Marks
   aDescribe the interaction mechanism between electron beam and RF field in a TWT.
   How to answer

   • TWT slow-wave helix structure and electron beam
   • Velocity synchronism between beam and RF wave
   • Bunching, energy exchange and growing wave amplification
   • Diagram of interaction along helix
4. 7 Marks
   bExplain the principle of operation of a Gunn Diode. Describe the various domains of operation and the Gunn effect.
   How to answer

   • Gunn effect: transferred electron mechanism and NDR
   • Principle of operation and domain formation
   • Various modes/domains: Gunn, LSA, transit-time, quenched
   • V-I characteristics and applications
5. 7 Marks
   aExplain the working principle and characteristics of a Schottky barrier diode. Discuss its use as a microwave mixer and detector.
   How to answer

   • Metal-semiconductor Schottky barrier formation
   • Working principle and I-V characteristics
   • Use as microwave mixer and detector
   • Advantages: low noise, fast switching
6. 7 Marks
   bDescribe the working of a Microwave Bipolar Junction Transistor (BJT). Discuss its frequency limitations and applications.
   How to answer

   • Structure of microwave BJT vs conventional BJT
   • Working at microwave frequencies
   • Frequency limitations: transit time, capacitances, cutoff frequency
   • Applications in amplifiers and oscillators
7. 7 Marks
   aDefine Scattering Matrix. Derive the general form of the scattering matrix for a reciprocal and lossless two-port microwave network.
   How to answer

   • Definition of scattering matrix with incident/reflected waves
   • Reciprocity condition Sij = Sji
   • Lossless unitary condition [S][S*]T = [I]
   • General 2-port form with magnitude and phase
8. 7 Marks
   bExplain the construction and working of a Slotted Line. How is it used to determine VSWR, wavelength and impedance?
   How to answer

   • Construction: slotted waveguide/coax with movable probe
   • Working: sampling standing wave field
   • Measurement of VSWR from max/min voltages
   • Determination of wavelength and load impedance
9. 7 Marks
   aExplain the construction and working of a Matching Network. Describe any two matching techniques used in microwave circuits.
   How to answer

   • Need for matching network and impedance matching
   • Construction and working principle
   • Two techniques: stub, quarter-wave, lumped, taper
   • Comparison of techniques
10. 7 Marks
    bDescribe the design and working of single and multi-section impedance transformers. Explain how bandwidth can be increased using multi-section design.
    How to answer

    • Single-section quarter-wave transformer design
    • Multi-section transformer theory
    • Bandwidth increase with multiple sections
    • Maximally flat / Chebyshev response
11. 7 Marks
    aExplain the Matched Hybrid Tee (Magic Tee). Derive its scattering matrix and explain how it combines the properties of E-plane and H-plane tees.
    How to answer

    • Matched hybrid tee combining E and H plane tees
    • Properties of ports and isolation
    • Derivation of 4x4 scattering matrix
    • Combining/splitting operation
12. 7 Marks
    bExplain the structure and working principle of a YIG Resonator. Discuss its frequency tuning characteristics and applications in microwave circuits.
    How to answer

    • YIG resonator structure: YIG sphere and coupling
    • Ferromagnetic resonance working principle
    • Frequency tuning by DC magnetic bias
    • Applications: filters, oscillators in microwave circuits
13. 7 Marks
    aDescribe the working principle of a microwave mixer. Discuss the roles of LO, RF and IF signals and explain the conversion loss.
    How to answer

    • Mixer principle: non-linear frequency translation
    • Roles of RF, LO to produce IF
    • Circuit operation and frequency relations
    • Conversion loss definition and causes
14. 7 Marks
    bExplain how oscillators are designed using S-parameters. Derive the oscillation condition in terms of reflection coefficients and feedback.
    How to answer

    • Oscillator design using S-parameters and stability
    • Reflection coefficient and negative resistance view
    • Derivation of oscillation condition $\Gamma_{in}\Gamma_L = 1$
    • Role of feedback and Barkhausen criterion
15. 14 Marks
    Write a short note on any two:

    1. (a))Magnetron
    2. (b))IMPATT Diode
    3. (c))S-parameters & its Applications
    4. (d))Diode Phase Shifters
    How to answer

    • Select any two topics with definition and principle
    • Construction/working and key formulas
    • Characteristics, advantages and limitations
    • Applications with neat diagram