Question 1(a) [3 marks]

Give comparison between transmission line and waveguide.

Answer:

Parameter	Transmission Line	Waveguide
Frequency Range	Low to medium frequencies	High frequencies (above 1 GHz)
Structure	Two or more conductors	Single hollow conductor
Propagation Mode	TEM mode	TE and TM modes
Power Handling	Limited power capacity	High power handling capability
Losses	Higher losses at high frequencies	Lower losses at microwave frequencies

Mnemonic: "WAVES Travel Better" (Waveguides - Advanced Versions Enabling Superior Transmission)

Question 1(b) [4 marks]

Define the following terms: (1) Lossless Line (2) VSWR (3) STUB (4) Reflection coefficient

Answer:

Lossless Line: A transmission line with zero resistance and conductance, having no power loss during signal transmission.
VSWR (Voltage Standing Wave Ratio): Ratio of maximum voltage to minimum voltage on a transmission line, indicating impedance mismatch.
STUB: Short length of transmission line connected to main line for impedance matching purposes.
Reflection Coefficient: Ratio of reflected wave amplitude to incident wave amplitude at any point on transmission line.

Mnemonic: "Light Volumes Stay Reflected" (Lossless-VSWR-Stub-Reflection)

Question 1(c) [7 marks]

Explain isolator and circulator with the help of sketch.

Answer:

graph LR
    A[Port 1] --> B[Isolator] --> C[Port 2]
    B -.X.-> A
    
    D[Port 1] --> E((Circulator)) --> F[Port 2]
    F --> G[Port 3] --> D

Isolator:

Function: Allows signal flow in one direction only
Construction: Uses ferrite material with magnetic bias
Applications: Protects sources from reflections

Circulator:

Function: Routes signals in circular pattern between three or four ports
Construction: Y-junction with ferrite material
Applications: Duplexers in radar systems

Mnemonic: "Isolated Circuits Flow Forward" (Isolator-Circulator-Forward-Flow)

Question 1(c OR) [7 marks]

What is dominant mode in a waveguide? What will be the cutoff wavelength for dominant mode, in a rectangular waveguide whose breadth is 10 cm? For a 2.5 GHz signal propagated through it calculate guide wavelength, group velocity and phase velocity and Z₀.

Answer:

Dominant Mode: Lowest order mode that can propagate in a waveguide. For rectangular waveguide, it's TE₁₀ mode.

Given Data:

Breadth (a) = 10 cm = 0.1 m
Frequency (f) = 2.5 GHz = 2.5 × 10⁹ Hz
c = 3 × 10⁸ m/s

Calculations:

Parameter	Formula	Value
Cutoff Wavelength	λc = 2a	λc = 2 × 0.1 = 0.2 m
Free Space Wavelength	λ₀ = c/f	λ₀ = 0.12 m
Guide Wavelength	λg = λ₀/√(1-(λ₀/λc)²)	λg = 0.133 m
Group Velocity	vg = c√(1-(λ₀/λc)²)	vg = 2.7 × 10⁸ m/s
Phase Velocity	vp = c/√(1-(λ₀/λc)²)	vp = 3.33 × 10⁸ m/s

Mnemonic: "Dominant Modes Calculate Guide Parameters"

Question 2(a) [3 marks]

What is single stub impedance matching, and how does it work?

Answer:

Single Stub Matching: Technique using one short-circuited or open-circuited stub connected in parallel to transmission line for impedance matching.

Working Principle:

Stub acts as reactive element (inductive or capacitive)
Cancels reactive component of load impedance
Transforms impedance to characteristic impedance

Mnemonic: "Single Stubs Transform Reactance" (Single-Stub-Transform-Reactive)

Question 2(b) [4 marks]

Differentiate between rectangular and circular waveguide any three points.

Answer:

Parameter	Rectangular Waveguide	Circular Waveguide
Cross-section	Rectangular shape	Circular shape
Dominant Mode	TE₁₀ mode	TE₁₁ mode
Field Pattern	Simple field distribution	Complex field distribution
Manufacturing	Easy to manufacture	Difficult to manufacture

Mnemonic: "Rectangles Dominate Ten" vs "Circles Dominate Eleven"

Question 2(c) [7 marks]

Explain the construction and working of Hybrid Ring with diagram.

Answer:

graph TD
    A[Port 1] --- B[Hybrid Ring]
    C[Port 2] --- B
    D[Port 3] --- B
    E[Port 4] --- B
    B -.-> F[λ/4 sections]

Construction:

Ring structure with four ports
Circumference = 1.5λ (one and half wavelengths)
Adjacent ports separated by λ/4
Opposite ports separated by 3λ/4

Working:

Power division: Input at one port divides equally between two adjacent ports
Isolation: Opposite port receives no power
Phase relationship: 180° phase difference between output ports

Applications:

Balanced mixers
Power combiners/dividers
Antenna feeds

Mnemonic: "Hybrid Rings Divide Power Equally"

Question 2(a OR) [3 marks]

What is Microwave? List out any four applications of microwave.

Answer:

Microwave: Electromagnetic waves with frequency range from 1 GHz to 300 GHz.

Applications:

Radar systems for detection and ranging
Satellite communication for long-distance transmission
Microwave ovens for heating food
Mobile communication (cellular networks)

Mnemonic: "Microwaves Reach Space Mobile" (Microwave-Radar-Satellite-Mobile)

Question 2(b OR) [4 marks]

Write short note on cavity resonator.

Answer:

Cavity Resonator: Closed metallic structure that confines electromagnetic energy at specific resonant frequencies.

Construction:

Metallic enclosure of specific dimensions
High Q factor (low losses)
Resonant frequency depends on cavity dimensions

Types:

Rectangular cavity
Cylindrical cavity
Spherical cavity

Applications:

Frequency meters
Oscillator circuits
Filter circuits

Mnemonic: "Cavities Resonate High Quality" (Cavity-Resonant-High-Q)

Question 2(c OR) [7 marks]

Explain MAGIC TEE with the help of sketch and how it works as an isolator?

Answer:

graph TD
    A[E-arm] --- B[Magic Tee Junction]
    C[H-arm] --- B
    D[Arm 1] --- B
    E[Arm 2] --- B

Magic Tee Construction:

E-plane Tee and H-plane Tee combined
Four ports: E-arm, H-arm, and two side arms
E-arm perpendicular to H-arm

Working as Isolator:

Signal at E-arm divides equally between side arms (in-phase)
Signal at H-arm divides equally between side arms (out-of-phase)
Isolation between E-arm and H-arm
No coupling between perpendicular arms

Properties:

Matched at all ports
Reciprocal device
Power division and isolation

Mnemonic: "Magic Isolates Perpendicular Arms"

Question 3(a) [3 marks]

Describe the working principle of MASER.

Answer:

MASER (Microwave Amplification by Stimulated Emission of Radiation):

Population inversion created in active medium
Stimulated emission produces coherent microwaves
Amplification occurs through energy level transitions

Working Principle:

Atoms excited to higher energy levels
Stimulated photons trigger emission
Coherent amplification of microwave signals

Mnemonic: "Microwaves Amplify Stimulated Emission Radiation"

Question 3(b) [4 marks]

List four microwave diodes and explain any one.

Answer:

Four Microwave Diodes:

GUNN Diode
IMPATT Diode
TRAPATT Diode
PIN Diode

GUNN Diode Explanation:

Principle: Transferred electron effect in GaAs
Construction: N-type GaAs with ohmic contacts
Operation: Negative resistance at microwave frequencies
Applications: Oscillators, amplifiers

VI Characteristic:

    I ^
      |    /
      |   /
      |  /___
      | /    \
      |/      \___
      +----------> V
      Negative resistance region

Mnemonic: "GUNN Generates Negative Resistance"

Question 3(c) [7 marks]

Write a detailed explanation of the Magnetron Oscillator, covering its construction, working principle, and applications?

Answer:

graph LR
    A[Cathode] --> B[Interaction Space]
    B --> C[Anode with Cavities]
    C --> D[Output Coupling]
    E[Magnetic Field] -.-> B

Construction:

Cylindrical cathode at center
Anode with resonant cavities surrounding cathode
Strong magnetic field perpendicular to electric field
Output coupling through waveguide

Working Principle:

Electrons emitted from heated cathode
Cycloid motion due to crossed E and B fields
Bunching effect creates electron clouds
Energy transfer from electrons to RF field
Oscillation at cavity resonant frequency

Applications:

Radar transmitters
Microwave ovens
Industrial heating
Medical diathermy

Mnemonic: "Magnetrons Make Microwave Oscillations"

Question 3(a OR) [3 marks]

Describe the working of RUBY MASER.

Answer:

Ruby MASER Working:

Ruby crystal (Al₂O₃ with Cr³⁺ ions) as active medium
Three energy levels in chromium ions
Pump frequency creates population inversion
Signal amplification at 2.9 GHz

Process:

Optical pumping excites electrons to higher level
Stimulated emission produces coherent microwaves
Low noise amplification achieved

Mnemonic: "Ruby Radiates Amplified Microwaves"

Question 3(b OR) [4 marks]

Draw and explain the VI characteristic of Gun diode

Answer:

    I ^
      |      
      |    B /
      |     /
      |    /
      | A /
      |  /
      | /_____ C
      |/      \
      |        \_____ D
      +-----------> V
    Valley    Peak
    Current   Current

VI Characteristic Explanation:

Region OA: Ohmic region (positive resistance)
Region AB: Negative resistance region
Region BC: Valley current region
Region CD: Saturation region

Key Points:

Peak voltage: Maximum voltage before negative resistance
Valley current: Minimum current in negative resistance region
Negative resistance: Current decreases with increasing voltage

Mnemonic: "Valley Peak Negative Resistance"

Question 3(c OR) [7 marks]

Explain "frequency measurement method" as well as "attenuation measurement method" at microwave frequency.

Answer:

Frequency Measurement Methods:

Method	Principle	Accuracy
Cavity Wavemeter	Resonant cavity tuning	High
Direct Reading Meter	Frequency counter	Very High
Heterodyne Method	Beat frequency technique	Medium

Attenuation Measurement Methods:

Method	Description	Application
Substitution Method	Replace attenuator with calibrated attenuator	Precision measurement
Power Ratio Method	Compare input and output power	General purpose
RF Bridge Method	Balance bridge circuit	Laboratory use

Setup for Measurement:

Signal generator provides test signal
Calibrated attenuator for reference
Power meter measures signal levels
VSWR meter monitors impedance matching

Mnemonic: "Frequency Attenuation Measured Precisely"

Question 4(a) [3 marks]

Explain working of P-i-N diode.

Answer:

P-i-N Diode Structure:

P-type region (heavily doped)
Intrinsic region (undoped, high resistance)
N-type region (heavily doped)

Working:

Forward bias: Low resistance, acts as conductor
Reverse bias: High resistance, acts as insulator
RF switching: Fast switching due to charge storage

Applications:

RF switches
Attenuators
Phase shifters

Mnemonic: "PIN Provides Instant Switching"

Question 4(b) [4 marks]

Explain π mode oscillations for magnetron.

Answer:

π Mode Oscillation:

Adjacent cavities oscillate 180° out of phase
Electron bunching synchronized with RF field
Maximum power transfer from electrons to RF
Stable oscillation at designed frequency

Characteristics:

Phase difference: π radians between adjacent cavities
Frequency: Determined by cavity dimensions
Efficiency: Highest among all modes
Stability: Most stable oscillation mode

Mode Chart:

Cavity: 1  2  3  4  5  6  7  8
Phase:  0  π  0  π  0  π  0  π

Mnemonic: "Pi Mode Produces Maximum Power"

Question 4(c) [7 marks]

Explain the construction and working of two cavity klystron amplifiers with necessary diagram.

Answer:

graph LR
    A[Electron Gun] --> B[Input Cavity]
    B --> C[Drift Space]
    C --> D[Output Cavity]
    D --> E[Collector]
    F[Input Signal] --> B
    D --> G[Output Signal]

Construction:

Electron gun produces electron beam
Input cavity (buncher) modulates electron beam
Drift space allows velocity modulation
Output cavity (catcher) extracts RF energy
Collector collects spent electrons

Working Principle:

Velocity modulation in input cavity
Electron bunching in drift space
Density modulation creates current variation
Energy extraction in output cavity
Amplification achieved through beam-field interaction

Key Parameters:

Beam voltage: Determines electron velocity
Cavity tuning: Sets operating frequency
Drift space length: Controls bunching effectiveness

Applications:

Radar transmitters
Satellite communication
Linear accelerators

Mnemonic: "Klystrons Amplify Through Bunching"

Question 4(a OR) [3 marks]

Explain parametric amplifier.

Answer:

Parametric Amplifier:

Variable reactance device using varactor diode
Pump frequency modulates diode capacitance
Energy transfer from pump to signal
Low noise amplification achieved

Working:

Pump power varies diode reactance
Signal mixing produces sum and difference frequencies
Idler frequency fp = fs + fi
Power gain through nonlinear mixing

Advantages:

Very low noise figure
High gain possible
Wide bandwidth

Mnemonic: "Parametric Amplifiers Pump Low Noise"

Question 4(b OR) [4 marks]

Draw and explain schematic diagram of travelling wave tube with necessary notation

Answer:

graph LR
    A[Electron Gun] --> B[Input]
    B --> C[Helix]
    C --> D[Output]
    D --> E[Collector]
    F[Attenuator] -.-> C
    G[Focusing System] -.-> C

Components:

Electron gun: Produces electron beam
Helix: Slow-wave structure
Attenuator: Prevents oscillation
Collector: Collects electrons
Focusing system: Maintains beam alignment

Working:

Electron beam travels through helix center
RF signal propagates along helix
Synchronism between beam and RF wave
Energy transfer from beam to RF
Continuous amplification along helix length

Mnemonic: "TWT Travels With Waves"

Question 4(c OR) [7 marks]

Explain the working principle of a reflex klystron in detail with suitable diagram.

Answer:

graph LR
    A[Cathode] --> B[Resonant Cavity]
    B --> C[Drift Space]
    C --> D[Repeller]
    D -.-> C
    C -.-> B
    B --> E[Output]

Construction:

Single resonant cavity acts as buncher and catcher
Repeller electrode reflects electron beam
Drift space allows velocity modulation
Output coupling extracts RF power

Working Principle:

Applegate Diagram:

Distance ^
         |    ___
         |   /   \  Bunched electrons
         |  /     \
         | /       \
         |/         \___
         +-------------> Time
         Transit time variation

Process:

Electrons enter cavity and get velocity modulated
Electrons drift toward repeller
Repeller reflects electrons back to cavity
Transit time determines bunching phase
Bunched electrons deliver energy to cavity
Oscillation maintained through feedback

Frequency Tuning:

Repeller voltage controls transit time
Cavity tuning sets center frequency
Electronic tuning possible

Applications:

Local oscillators
Frequency meters
Microwave sources

Mnemonic: "Reflex Returns Electron Bunches"

Question 5(a) [3 marks]

"PIN diode acts as a switch and VARACTOR diode acts as a variable capacitor" explain.

Answer:

PIN Diode as Switch:

Forward bias: Low resistance (~1Ω), switch ON
Reverse bias: High resistance (~10kΩ), switch OFF
Fast switching due to charge storage in I-region
RF isolation in OFF state

VARACTOR Diode as Variable Capacitor:

Reverse bias voltage controls junction capacitance
Capacitance decreases with increasing reverse voltage
Voltage-controlled reactance for tuning circuits
Electronic tuning without mechanical adjustment

Mnemonic: "PIN Switches, VARACTOR Varies"

Question 5(b) [4 marks]

List the display methods used in RADAR and explain any one.

Answer:

RADAR Display Methods:

A-Scope Display
PPI (Plan Position Indicator)
B-Scope Display
RHI (Range Height Indicator)

PPI Display Explanation:

Circular display showing target positions
Center represents radar location
Radial distance indicates target range
Angular position shows target bearing
Rotating sweep synchronized with antenna rotation

Features:

Real-time display of target positions
Range and bearing information
Multiple target tracking
Clutter suppression

Mnemonic: "PPI Pictures Position Indicators"

Question 5(c) [7 marks]

What is radar? List out the different types of radar systems? Explain any One of radar in detail?

Answer:

RADAR (Radio Detection And Ranging): System using radio waves to detect objects and determine their range, velocity, and characteristics.

Types of RADAR Systems:

Type	Application	Frequency Band
Pulse Radar	Air traffic control	L, S, C bands
CW Doppler Radar	Speed measurement	X, K, Ka bands
MTI Radar	Moving target detection	S, C bands
SAR Radar	Ground mapping	L, C, X bands

Pulse Radar Detailed Explanation:

graph LR
    A[Transmitter] --> B[Duplexer]
    B --> C[Antenna]
    C --> D[Target]
    D --> C
    C --> B
    B --> E[Receiver]
    E --> F[Display]
    G[Timer] --> A
    G --> F

Working:

Transmits short pulses of RF energy
Receives echoes from targets
Measures time delay for range calculation
Processes signals for display

Range Equation: R = (c × t)/2

Where:

R = Range to target
c = Speed of light
t = Time delay

Applications:

Air traffic control
Weather monitoring
Military surveillance
Navigation aids

Mnemonic: "Radar Ranges Radio Waves"

Question 5(a OR) [3 marks]

Describe the operation of TRAPATT diode with diagram.

Answer:

    I ^
      |      |\
      |      | \
      |      |  \
      |      |   \__ Trapped plasma
      |      |     \ avalanche
      |______|______\___
      +----------------> V
      Breakdown voltage

TRAPATT Operation:

TRApped Plasma Avalanche Triggered Transit diode
High field region creates avalanche breakdown
Plasma formation traps charge carriers
Transit time effects create negative resistance
Oscillation frequency determined by transit time

Applications:

High power oscillators
Radar transmitters
Communication systems

Mnemonic: "TRAPATT Traps Plasma Avalanche"

Question 5(b OR) [4 marks]

Compare RADAR with SONAR.

Answer:

Parameter	RADAR	SONAR
Wave Type	Electromagnetic waves	Sound waves
Medium	Air/vacuum	Water/liquid
Frequency	GHz range	kHz range
Speed	3 × 10⁸ m/s	1500 m/s in water
Range	Very long range	Limited by absorption
Applications	Air/space detection	Underwater detection

Similarities:

Echo principle for detection
Range measurement using time delay
Doppler effect for velocity measurement

Mnemonic: "RADAR Radiates, SONAR Sounds"

Question 5(c OR) [7 marks]

Obtain the equation for maximum radar range.

Answer:

RADAR Range Equation Derivation:

Power Transmitted: Pt

Power Density at Target: Pd = Pt/(4πR²)

Power Intercepted by Target: Pi = Pd × σ = (Pt × σ)/(4πR²)

Power Returned to Radar: Pr = Pi/(4πR²) = (Pt × σ)/(4πR²)²

Power Received: Pr = (Pt × G² × λ² × σ)/((4π)³ × R⁴)

Maximum Range Equation:

Rmax = ⁴√[(Pt × G² × λ² × σ)/((4π)³ × Prmin)]

Where:

Pt = Transmitted power
G = Antenna gain
λ = Wavelength
σ = Radar cross section
Prmin = Minimum detectable signal
R = Range

Factors Affecting Range:

Transmitted power (increases range)
Antenna gain (increases range)
Target cross-section (increases range)
Frequency (affects propagation)
Receiver sensitivity (affects minimum signal)

Practical Considerations:

Atmospheric losses
Ground reflections
Noise limitations
Clutter effects

Mnemonic: "Power Gain Lambda Sigma Range"