Microwave and Radar Communication (4351103) - Winter 2023 Solution

Question 1(a) [3 marks]

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Sketch the standing wave pattern for voltage and current along the transmission line when it is terminated with (i) Short Circuit, (ii) Open circuit, and (iii) Matched Load.

Answer:

Diagram:

• Short Circuit: Voltage minimum at load, current maximum at load
• Open Circuit: Voltage maximum at load, current minimum at load
• Matched Load: Constant voltage and current, no reflections

Mnemonic: “SOC - Short Opens Current, Open Shorts Current”

Question 1(b) [4 marks]

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Draw and Explain equivalent circuit of two parallel wire transmission line at microwave frequency.

Answer:

Diagram:

• R: Series resistance per unit length (conductor losses)
• L: Series inductance per unit length (magnetic field storage)
• G: Shunt conductance per unit length (dielectric losses)
• C: Shunt capacitance per unit length (electric field storage)

Primary Constants Table:

Mnemonic: “RLGC - Really Largeガイド Cables”

Question 1(c) [7 marks]

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Explain Principle, construction and working of Isolator with necessary sketch.

Answer:

Principle: Isolator allows microwave signal to pass in forward direction only using ferrite material and Faraday rotation effect.

Construction Diagram:

graph TD
    A[Input Port] --> B[Ferrite Rod]
    B --> C[Permanent Magnet]
    C --> D[Output Port]
    E[Resistive Load] --> B
    F[Waveguide] --> B

Working:

• Forward direction: Signal passes through ferrite with minimal loss
• Reverse direction: Signal is rotated 45° and absorbed by resistive load
• Magnetic field biases ferrite material
• Isolation: 20-30 dB typical

Applications:

• Protects transmitter from reflected power
• Prevents oscillations in amplifier circuits
• Maintains source impedance matching

Specifications Table:

Mnemonic: “Isolate Forward, Absorb Reverse”

Question 1(c OR) [7 marks]

#

Compare Transmission Line and Waveguide.

Answer:

Comparison Table:

Key Differences:

• Transmission line: Uses two conductors, supports TEM mode
• Waveguide: Single hollow conductor, supports TE/TM modes
• Cutoff frequency: Waveguide has minimum operating frequency
• Field pattern: Different electromagnetic field distributions

Applications:

• Transmission lines: Low power, broadband applications
• Waveguides: High power radar, satellite communication

Mnemonic: “Transmission Travels Two-wire, Waveguide Walks Wide”

Question 2(a) [3 marks]

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Define: (i) VSWR, (ii) Reflection Coefficient, and (iii) Skin effect

Answer:

Definitions:

• VSWR (Voltage Standing Wave Ratio): Ratio of maximum to minimum voltage amplitudes on transmission line

  • Formula: VSWR = V_max/V_min = (1+|Γ|)/(1-|Γ|)

• Reflection Coefficient (Γ): Ratio of reflected to incident voltage amplitude

  • Formula: Γ = (Z_L - Z_0)/(Z_L + Z_0)

• Skin Effect: Current flows mainly on conductor surface at high frequencies

  • Skin depth: δ = √(2/ωμσ)

Parameters Table:

Mnemonic: “VSWR Varies, Gamma Guides, Skin Shrinks”

Question 2(b) [4 marks]

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Explain working of Two-hole Directional Coupler with Proper sketch.

Answer:

Construction Diagram:

Working Principle:

• Two holes spaced λ/4 apart couple energy between waveguides
• Forward wave: Coupled signals add at P3, cancel at P4
• Reverse wave: Coupled signals add at P4, cancel at P3
• Directivity: Achieved by proper hole spacing and size

Coupling Mechanism:

• Electric field coupling through holes
• Phase difference creates directional coupling
• Coupling factor: C = 10 log(P1/P3) dB

Performance Parameters:

Mnemonic: “Two Holes, Two Directions, Total Control”

Question 2(c) [7 marks]

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Describe Propagation of microwaves through waveguide and get the equation of cut off wavelength.

Answer:

Propagation Theory: Electromagnetic waves propagate through waveguide in TE and TM modes with specific field patterns.

Wave Equation: For rectangular waveguide, the wave equation is: ∇²E + γ²E = 0

Where γ² = β² - k²

Cutoff Wavelength Derivation:

For TE_mn mode in rectangular waveguide:

• Cutoff frequency: f_c = (c/2)√[(m/a)² + (n/b)²]
• Cutoff wavelength: λ_c = 2/√[(m/a)² + (n/b)²]

For dominant TE₁₀ mode:

• λ_c = 2a (where a is broad dimension)

Propagation Conditions:

• Below cutoff (f < f_c): Evanescent wave, exponential decay
• Above cutoff (f > f_c): Propagating wave
• Phase velocity: v_p = c/√[1 - (f_c/f)²]
• Group velocity: v_g = c√[1 - (f_c/f)²]

Mode Chart:

graph LR
    A[TE₁₀] --> B[TE₂₀]
    A --> C[TE₀₁]
    B --> D[TE₁₁]
    C --> D

Key Relations:

• v_p × v_g = c²
• λ_g = λ₀/√[1 - (λ₀/λ_c)²]

Mnemonic: “Cut-off Comes, Propagation Proceeds”

Question 2(a OR) [3 marks]

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Explain Impedance Matching using Single stub.

Answer:

Principle: Single stub matching uses a short-circuited or open-circuited stub to cancel reactive component of load impedance.

Stub Diagram:

Design Steps:

• Step 1: Find distance ’d’ where normalized conductance = 1
• Step 2: Calculate required stub susceptance: B_s = -B_load
• Step 3: Determine stub length: l_s from B_s

Smith Chart Method:

• Plot normalized load impedance
• Move toward generator to find matching point
• Add stub susceptance to achieve center point

Mnemonic: “Single Stub Solves Susceptance”

Question 2(b OR) [4 marks]

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Explain Hybrid ring with necessary sketch.

Answer:

Construction Diagram:

graph TB
    A[Port 1] --> B[Ring Junction]
    C[Port 2] --> B
    D[Port 3] --> B
    E[Port 4] --> B
    B --> F[3λ/2 Ring Path]

Working Principle:

• Ring circumference: 3λ/2 (1.5 wavelengths)
• Equal path lengths from each port to opposite port
• 180° phase difference between adjacent ports

S-Matrix Properties:

• Isolation: Ports 1-3 and ports 2-4 are isolated
• Power division: Equal split with 180° phase difference
• Impedance: All ports matched to Z₀

Applications:

• Balanced mixers
• Push-pull amplifiers
• Phase comparison circuits

Performance Table:

Mnemonic: “Ring Rotates, Ports Pair-up”

Question 2(c OR) [7 marks]

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Explain construction, working and any one application of Magic Tee with necessary diagram.

Answer:

Construction: Magic Tee is formed by joining E-plane and H-plane tees at their junction.

Structure Diagram:

Working Principle:

• Ports 1,2: Collinear arms (input/output ports)
• Port 3: H-arm (sum/Σ port)
• Port 4: E-arm (difference/Δ port)
• Isolation: Between sum and difference ports

S-Matrix Properties:

graph LR
    A[Port 1] -.->|In phase| B[H-arm]
    C[Port 2] -.->|In phase| B
    A -->|Out of phase| D[E-arm]
    C -->|180° phase| D

Application - Radar Duplexer:

• Transmit: Power fed to H-arm, splits equally to ports 1,2
• Receive: Received signals combine at E-arm for receiver
• Isolation: Protects receiver during transmission
• Advantage: Single antenna for transmit/receive

Performance Specifications:

Key Features:

• Symmetric structure ensures equal power division
• Orthogonal fields provide port isolation
• Broadband operation over octave bandwidth

Mnemonic: “Magic Makes Isolation, Tee Transmits Together”

Question 3(a) [3 marks]

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Explain Attenuation measurement with the help of block diagram.

Answer:

Block Diagram:

graph LR
    A[Signal Generator] --> B[Attenuator Under Test]
    B --> C[Power Meter]
    D[Reference Path] --> C
    E[Switch] --> B
    E --> D

Measurement Procedure:

• Step 1: Measure power without attenuator (P₁)
• Step 2: Insert attenuator, measure power (P₂)
• Step 3: Calculate attenuation = 10 log(P₁/P₂) dB

Methods:

• Substitution method: Compare with known attenuator
• Direct method: Measure input and output power
• IF substitution: Use intermediate frequency

Mnemonic: “Attenuation = Power₁/Power₂”

Question 3(b) [4 marks]

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Explain velocity modulation in two cavity klystron with the help of Applegate diagram.

Answer:

Two Cavity Klystron Diagram:

Applegate Diagram:

Velocity Modulation Process:

• Input cavity: Electrons gain/lose energy from RF field
• Drift space: Fast electrons catch up to slow electrons
• Bunching: Electron density varies periodically
• Output cavity: Bunched electrons induce RF current

Key Parameters:

• Transit time: τ = L/v₀ (where L = drift space length)
• Bunching parameter: X = βn/2
• Optimum bunching: X = 1.84

Mnemonic: “Velocity Varies, Bunching Builds”

Question 3(c) [7 marks]

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Explain the principle, construction and effect of electric and magnetic field in Magnetron.

Answer:

Principle: Magnetron uses crossed electric and magnetic fields to generate high-power microwave oscillations through cyclotron motion of electrons.

Construction Diagram:

Field Effects:

• Electric Field (E): Radial, from cathode to anode
• Magnetic Field (B): Axial, perpendicular to E-field
• Crossed fields: Create cycloidal electron motion

Electron Motion Analysis:

graph TD
    A[Electron Emission] --> B[Cyclotron Motion]
    B --> C[Spiral Path]
    C --> D[Energy Transfer]
    D --> E[RF Oscillation]

Operating Conditions:

• Cutoff condition: E/B = v_drift
• Synchronism: Electron drift velocity matches phase velocity
• Hull cutoff: Minimum magnetic field for operation

Resonant Cavities:

• π-mode operation: Alternate cavities have opposite phases
• Frequency: f = c/(2√LC) for cavity resonance
• Mode separation: Prevents mode competition

Performance Characteristics:

Advantages:

• High efficiency compared to other tubes
• High power capability
• Compact structure
• Good frequency stability

Applications:

• Radar transmitters
• Microwave ovens
• Industrial heating
• Electronic warfare

Mnemonic: “Magnetron Makes Microwaves via Magnetic Motion”

Question 3(a OR) [3 marks]

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Explain working of TWT (Travelling Wave Tube) as an Amplifier.

Answer:

TWT Structure:

graph LR
    A[Electron Gun] --> B[Helix]
    B --> C[Collector]
    D[RF Input] --> B
    B --> E[RF Output]

Amplification Process:

• Electron beam travels along helix axis
• RF signal propagates along helix (slow wave structure)
• Velocity synchronism: v_electron ≈ v_RF
• Energy transfer from DC beam to RF wave

Gain Mechanism:

• Bunching: RF field modulates electron velocity
• Induced current: Bunched electrons induce RF current in helix
• Progressive amplification along helix length

Mnemonic: “Travelling Wave Transfers Energy”

Question 3(b OR) [4 marks]

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Explain Bolometer method for low power measurement at microwave frequency.

Answer:

Principle: Bolometer measures microwave power by detecting temperature rise in resistive element.

Bolometer Types:

• Thermistor: Negative temperature coefficient
• Barretter: Positive temperature coefficient

Circuit Diagram:

Measurement Process:

• Step 1: Balance bridge with DC power only
• Step 2: Apply RF power, note bridge unbalance
• Step 3: Reduce DC power to rebalance bridge
• Step 4: RF power = Reduction in DC power

Advantages:

• High sensitivity (µW to mW range)
• Square law response
• Broadband operation

Mnemonic: “Bolometer Burns, Bridge Balances”

Question 3(c OR) [7 marks]

#

Explain frequency and wavelength measurement method with the help of block diagram.

Answer:

Frequency Measurement - Direct Method:

graph LR
    A[Microwave Source] --> B[Frequency Counter]
    B --> C[Digital Display]
    D[Reference Oscillator] --> B

Frequency Measurement - Heterodyne Method:

graph LR
    A[Unknown Frequency] --> B[Mixer]
    C[Local Oscillator] --> B
    B --> D[IF Amplifier]
    D --> E[Frequency Counter]

Wavelength Measurement - Slotted Line Method:

Setup Diagram:

Measurement Procedure:

Free Space Wavelength (λ₀):

• Step 1: Connect matched load, measure frequency
• Step 2: Calculate λ₀ = c/f

Guided Wavelength (λ_g):

• Step 1: Connect short circuit, find two consecutive minima
• Step 2: λ_g = 2 × distance between minima
• Step 3: Verify: λ_g = λ₀/√[1-(λ₀/λ_c)²]

Cut-off Wavelength (λ_c):

• Method 1: From waveguide dimensions: λ_c = 2a (for TE₁₀)
• Method 2: From λ₀ and λ_g: λ_c = λ₀/√[1-(λ₀/λ_g)²]

Measurement Table:

Advantages of Each Method:

• Direct method: High accuracy, simple
• Heterodyne method: Extended frequency range
• Slotted line: Measures guided parameters directly

Error Sources:

• Probe coupling variations
• Temperature effects on dimensions
• Detector nonlinearity
• Standing wave disturbances

Applications:

• Waveguide characterization
• Material property measurement
• Antenna testing
• Component verification

Mnemonic: “Frequency First, Wavelength With-measurement”

Question 4(a) [3 marks]

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State Frequency limitations of vacuum tubes at microwave frequency.

Answer:

Frequency Limitations:

• Transit time effects: Electron transit time becomes comparable to RF period
• Inter-electrode capacitance: Reduces gain at high frequencies
• Lead inductance: Parasitic inductances limit performance
• Skin effect: Current concentration reduces effective conductance

Limiting Factors Table:

Solutions:

• Reduce electrode spacing
• Use special geometries
• Employ microwave tubes (Klystron, Magnetron)

Mnemonic: “Transit Time Troubles Traditional Tubes”

Question 4(b) [4 marks]

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Explain Negative resistance effect in IMPATT Diode.

Answer:

IMPATT Structure:

Negative Resistance Mechanism:

Two-step Process:

1. Impact Ionization: High field creates electron-hole pairs
2. Transit Time Delay: Carriers drift across depletion region

Phase Relationships:

• Current: Lags voltage by 90° (avalanche delay) + 90° (transit delay) = 180°
• Result: I = -G*V (negative conductance)

Operating Cycle:

graph LR
    A[High Field] --> B[Avalanche]
    B --> C[Carrier Generation]
    C --> D[Transit Delay]
    D --> E[Current Peak]
    E --> A

Key Parameters:

• Avalanche frequency: f_a = v_s/(2W_a)
• Transit frequency: f_t = v_d/(2W_d)
• Optimum frequency: f_0 = 1/(2π√L*|C_negative|)

Mnemonic: “Impact Ionization, Transit Time = Negative Resistance”

Question 4(c) [7 marks]

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Explain Principle, tunneling phenomenon and any one application of Tunnel Diode.

Answer:

Principle: Tunnel diode operates on quantum mechanical tunneling effect through thin potential barrier in heavily doped p-n junction.

Energy Band Diagram:

I-V Characteristics:

Tunneling Phenomenon:

Quantum Mechanics: Electrons can penetrate potential barrier even if their energy is less than barrier height.

Tunneling Probability: T = exp(-2√(2mφd²)/ħ) Where:

• m = electron mass
• φ = barrier height
• d = barrier width
• ħ = reduced Planck constant

Operating Regions:

• Tunneling region (0 to Vp): Current increases with voltage
• Negative resistance (Vp to Vv): Current decreases with increasing voltage
• Forward bias (>Vv): Normal diode behavior

Key Parameters Table:

Application - High Frequency Oscillator:

Circuit Diagram:

Oscillator Operation:

• Bias point: Set in negative resistance region
• Tank circuit: LC determines oscillation frequency
• Condition: |R_negative| > R_positive for oscillation
• Frequency: f = 1/(2π√LC)

Advantages:

• Ultra-high frequency operation (up to 100 GHz)
• Low noise figure
• Fast switching (picosecond range)
• Low power consumption
• Temperature stable

Applications:

• Microwave oscillators
• High-speed switches
• Microwave amplifiers
• Frequency converters
• Computer memory circuits

Limitations:

• Low power handling
• Critical bias requirements
• Limited temperature range
• Expensive manufacturing

Design Considerations:

• Doping concentration: >10¹⁹ cm⁻³ for both sides
• Junction area: Small for high frequency operation
• Parasitic elements: Minimize package inductance/capacitance
• Bias stability: Temperature compensation required

Mnemonic: “Tunnel Through, Negative Grows, Oscillator Flows”

Question 4(a OR) [3 marks]

#

Explain Hazards due to microwave radiation.

Answer:

Types of Hazards:

HERP (Hazards of Electromagnetic Radiation to Personnel):

• Thermal effects: Tissue heating above 41°C
• Non-thermal effects: Cellular damage at low power levels
• Cumulative effects: Long-term exposure risks

HERO (Hazards of Electromagnetic Radiation to Ordnance):

• Premature ignition: RF energy can trigger explosive devices
• Fuel ignition: Microwave heating of fuel vapors
• Electronic interference: Disruption of control systems

HERF (Hazards of Electromagnetic Radiation to Fuels):

• Fuel heating: Dielectric heating of hydrocarbon fuels
• Static discharge: RF-induced sparking in fuel systems
• Vapor ignition: Heating of fuel-air mixtures

Safety Guidelines Table:

Mnemonic: “HERP-HERO-HERF = Health-Explosive-Fuel Risks”

Question 4(b OR) [4 marks]

#

Explain Degenerate and non-degenerate mode in Parametric Amplifier.

Answer:

Parametric Amplifier Principle: Uses time-varying reactance to transfer energy from pump to signal.

Mode Classifications:

Non-degenerate Mode:

• Three frequencies: f_s (signal), f_i (idler), f_p (pump)
• Frequency relation: f_p = f_s + f_i
• Two separate circuits for signal and idler
• Higher gain but more complex

Degenerate Mode:

• Two frequencies: f_s (signal), f_p (pump)
• Frequency relation: f_p = 2f_s
• Single resonant circuit
• Simpler design but lower gain

Comparison Table:

Energy Transfer:

graph LR
    A[Pump Power] --> B[Variable Reactance]
    B --> C[Signal Amplification]
    D[Idler] -.-> B

Mnemonic: “Non-degenerate = Not-single, Degenerate = Doubled-frequency”

Question 4(c OR) [7 marks]

#

Explain principle and Gunn effect in Gunn Diode. Also Explain Gunn Diode as an Oscillator.

Answer:

Gunn Effect Principle: Based on transferred electron effect in compound semiconductors (GaAs, InP).

Energy Band Structure:

Gunn Effect Mechanism:

Differential Mobility:

• Low field (<3 kV/cm): Electrons in Γ valley (high mobility)
• High field (>3 kV/cm): Electrons transfer to L valley (low mobility)
• Result: Negative differential mobility (NDM)

Domain Formation:

graph TD
    A[Uniform Field] --> B[Instability]
    B --> C[Domain Nucleation]
    C --> D[Domain Growth]
    D --> E[Domain Transit]
    E --> F[Domain Collection]
    F --> A

Current-Voltage Characteristics:

Gunn Diode Oscillator:

Basic Configuration:

Oscillator Modes:

Transit Time Mode:

• Domain formation at cathode
• Domain transit across active region
• Current pulse when domain reaches anode
• Frequency: f = v_d/L (where v_d = drift velocity, L = length)

Quenched Domain Mode:

• Resonant circuit quenches domain before transit
• Higher frequency operation possible
• Efficiency: 5-20%

LSA (Limited Space-charge Accumulation) Mode:

• High frequency prevents domain formation
• Uniform field maintained
• Higher efficiency: 10-25%

Performance Parameters:

Advantages:

• Simple structure - no external resonator needed
• Broadband tuning capability
• Low noise at microwave frequencies
• Reliable operation

Applications:

• Local oscillators in receivers
• CW radar transmitters
• Microwave communication systems
• Test equipment signal sources

Design Considerations:

• Doping profile: Uniform n-type doping
• Length optimization: L = v_d/f for transit time mode
• Thermal management: Heat dissipation critical
• Circuit design: Impedance matching important

Comparison with Other Oscillators:

Mnemonic: “Gunn Gets Going via Gallium-Arsenide”

Question 5(a) [3 marks]

#

Explain working principle of Basic RADAR system with the help of block diagram.

Answer:

RADAR Principle: Radio Detection And Ranging - transmits RF pulses and detects reflected signals from targets.

Basic RADAR Block Diagram:

graph TD
    A[Master Oscillator] --> B[Modulator]
    B --> C[Power Amplifier]
    C --> D[Duplexer]
    D --> E[Antenna]
    E --> F[Target]
    F --> E
    E --> D
    D --> G[Receiver]
    G --> H[Signal Processor]
    H --> I[Display]
    J[Timing Control] --> B

Working Principle:

• Transmission: High power RF pulse transmitted toward target
• Propagation: EM wave travels at speed of light (c)
• Reflection: Target reflects portion of energy back to radar
• Reception: Reflected signal received and processed
• Range calculation: R = (c × t)/2

Key Parameters:

• Pulse width: τ = 0.1 to 10 μs
• Pulse repetition frequency: PRF = 100 Hz to 10 kHz
• Peak power: 1 kW to 10 MW

Mnemonic: “RADAR Ranges by Round-trip Reflection”

Question 5(b) [4 marks]

#

Explain A-scope display method with the help of proper figure.

Answer:

A-Scope Display: Shows amplitude vs time relationship of received echoes.

A-Scope Presentation:

Display Components:

• Main pulse: Initial transmitted pulse (reference)
• Ground clutter: Reflections from nearby terrain
• Sea clutter: Reflections from sea surface
• Target echo: Reflection from actual target
• Noise: Random background signals

Range Measurement:

• Horizontal axis: Time (proportional to range)
• Vertical axis: Signal amplitude
• Range formula: R = (c × t)/2

Applications:

• Air traffic control
• Height finding radars
• Range measurement
• Signal analysis

Mnemonic: “A-scope shows Amplitude Along time Axis”

Question 5(c) [7 marks]

#

Explain Doppler effect and working of MTI (Moving Target Indicator) RADAR system with the help of block diagram.

Answer:

Doppler Effect: Frequency shift occurs when there is relative motion between radar and target.

Doppler Frequency Shift: f_d = (2 × v_r × f_0)/c

Where:

• f_d = Doppler frequency shift
• v_r = radial velocity of target
• f_0 = transmitted frequency
• c = speed of light

Doppler Shift Cases:

• Approaching target: f_d > 0 (positive shift)
• Receding target: f_d < 0 (negative shift)
• Stationary target: f_d = 0 (no shift)

MTI RADAR Block Diagram:

graph TD
    A[Transmitter] --> B[Duplexer]
    B --> C[Antenna]
    C --> D[Target]
    D --> C
    C --> B
    B --> E[Receiver]
    F[STALO] --> G[Mixer 1]
    H[COHO] --> I[Phase Detector]
    E --> G
    G --> J[IF Amplifier]
    J --> K[Mixer 2]
    H --> K
    K --> L[Video Amplifier]
    L --> M[Delay Line]
    M --> N[Subtractor]
    L --> N
    N --> O[Display]
    P[Sync] --> A
    P --> H

MTI System Components:

STALO (Stable Local Oscillator):

• Frequency: Close to transmitted frequency
• Stability: High frequency stability required
• Function: First mixer LO

COHO (Coherent Oscillator):

• Phase reference: Maintains phase coherence
• Synchronization: Locked to transmitter phase
• Function: Second mixer LO and phase reference

MTI Processing:

• Delay line: Stores previous pulse echo
• Subtractor: Subtracts current from previous pulse
• Result: Stationary targets cancelled, moving targets enhanced

MTI Transfer Function:

Blind Speeds: Targets with certain velocities appear stationary: v_blind = (n × λ × PRF)/2 (where n = 1,2,3…)

Performance Improvements:

Multi-pulse MTI:

• Multiple delay lines for better clutter rejection
• Staggered PRF to reduce blind speeds
• Weighted coefficients for optimum response

Clutter Map:

• Digital memory stores clutter pattern
• Adaptive threshold adjusts to local clutter level
• Automatic updates track slow clutter changes

MTI Performance Metrics:

Advantages:

• Clutter suppression: Eliminates stationary clutter
• Moving target emphasis: Enhances moving targets
• Automatic operation: Reduces operator workload

Limitations:

• Blind speeds: Some velocities undetectable
• Tangential targets: No radial component
• Weather effects: Rain/snow can mask targets

Applications:

• Air traffic control: Separates aircraft from ground clutter
• Weather radar: Detects precipitation movement
• Military surveillance: Detects moving vehicles
• Marine radar: Reduces sea clutter

Mnemonic: “MTI Makes Targets Identifiable via Doppler Difference”

Question 5(a OR) [3 marks]

#

Define: a) Blind speed, and b) MUR

Answer:

Blind Speed:

• Definition: Target radial velocities that produce zero Doppler shift in MTI radar
• Formula: v_blind = (n × λ × PRF)/2
• Cause: Target motion synchronized with pulse repetition
• Result: Moving target appears stationary

MUR (Maximum Unambiguous Range):

• Definition: Maximum range at which targets can be detected without range ambiguity
• Formula: R_max = (c × PRT)/2 = c/(2 × PRF)
• Limitation: Next pulse transmitted before echo returns
• Ambiguity: Targets beyond MUR appear at incorrect range

Relationship Table:

Mnemonic: “Blind speed Blocks, MUR Measures maximum”

Question 5(b OR) [4 marks]

#

Explain the factors affecting Maximum RADAR range.

Answer:

RADAR Range Equation: R_max = [(P_t × G² × λ² × σ)/(64π³ × P_min × L)]^(1/4)

Factors Affecting Maximum Range:

Transmitted Power (P_t):

• Higher power = greater range
• Relationship: R ∝ P_t^(1/4)
• Limitation: Peak power limited by transmitter

Antenna Gain (G):

• Directional antenna concentrates energy
• Relationship: R ∝ G^(1/2)
• Trade-off: Higher gain = narrower beamwidth

Wavelength (λ):

• Lower frequency = better propagation
• Relationship: R ∝ λ^(1/2)
• Consideration: Atmospheric absorption increases with frequency

Target Cross Section (σ):

• Larger targets reflect more energy
• Relationship: R ∝ σ^(1/4)
• Variation: Depends on target shape, material, aspect angle

Factors Table:

Mnemonic: “Power-Gain-Lambda-Sigma determine Range”

Question 5(c OR) [7 marks]

#

Compare Pulsed RADAR and CW Doppler RADAR.

Answer:

Comprehensive Comparison:

Basic Principle:

• Pulsed RADAR: Transmits high-power pulses, measures round-trip time
• CW Doppler: Transmits continuous wave, measures Doppler frequency shift

System Block Diagrams:

Pulsed RADAR:

graph LR
    A[Pulse Generator] --> B[Transmitter]
    B --> C[Duplexer]
    C --> D[Antenna]
    C --> E[Receiver]
    E --> F[Display]

CW Doppler RADAR:

graph LR
    A[CW Oscillator] --> B[Directional Coupler]
    B --> C[Transmit Antenna]
    D[Receive Antenna] --> E[Mixer]
    B --> E
    E --> F[Audio Amplifier]
    F --> G[Display]

Detailed Comparison Table:

Performance Characteristics:

Advantages & Disadvantages:

Pulsed RADAR Advantages:

• Range measurement capability
• High peak power for long range
• Single antenna system
• Well-established technology

Pulsed RADAR Disadvantages:

• Complex circuitry (duplexer, timing)
• High cost and maintenance
• Power supply requirements
• Blind ranges due to pulse width

CW Doppler Advantages:

• Simple design and low cost
• Excellent velocity resolution
• Continuous monitoring
• Low power consumption
• Compact size

CW Doppler Disadvantages:

• No range information
• Separate antennas required
• Limited range capability
• Vulnerable to interference

Applications:

Pulsed RADAR Applications:

• Air traffic control
• Weather monitoring
• Military surveillance
• Maritime navigation
• Satellite tracking

CW Doppler Applications:

• Traffic speed monitoring
• Sports radar guns
• Burglar alarms
• Automatic door openers
• Heart rate monitoring

Hybrid Systems:

Pulse Doppler RADAR:

• Combines advantages of both systems
• Range and velocity measurement
• Higher complexity but better performance

FM-CW RADAR:

• Frequency modulated continuous wave
• Range capability added to CW system
• Used in automotive radar applications

Selection Criteria:

Future Trends:

• Digital signal processing improving both types
• Software-defined radars offering flexibility
• MIMO techniques enhancing performance
• Integration with other sensors

Mnemonic: “Pulsed gives Position, CW gives Continuous-Velocity”