Question 1(a) [3 marks]#
Define Beam Area and Beam Efficiency.
Answer:
Beam Area: The solid angle through which all of the power radiated by an antenna would flow if the radiation intensity was constant throughout this angle and equal to the maximum value.
Beam Efficiency: The ratio of the power contained in the main beam to the total power radiated by the antenna.
Diagram:
graph LR
A[Beam Area] --> B[Solid angle containing<br>most of the radiated power]
C[Beam Efficiency] --> D[Main Beam Power/Total Power]
D --> E[Higher efficiency = Better antenna]
Mnemonic: “BEAM: Better Efficiency Achieves Maximum performance”
Question 1(b) [4 marks]#
What is EM field? Explain its radiation from center fed dipole.
Answer:
EM field is a physical field produced by electrically charged objects that affects charged particles with a force.
Diagram:
- Electric field: Perpendicular to antenna axis, maximum at antenna ends
- Magnetic field: Circular around antenna axis
- Radiation mechanism: Alternating current creates time-varying fields
- Field behavior: Near field (reactive) → intermediate → far field (radiating)
Mnemonic: “CERD: Current Excites Radiating Dipole”
Question 1(c) [7 marks]#
Explain Power radiated by elementary dipole using Poynting Vector.
Answer:
Power radiated by an elementary dipole can be calculated using the Poynting vector, which represents power flow density.
Table: Key Steps in Poynting Vector Analysis
| Step | Description |
|---|---|
| 1 | Calculate E-field components (Eθ, Eφ) |
| 2 | Calculate H-field components (Hθ, Hφ) |
| 3 | Determine Poynting vector: P = E × H |
| 4 | Integrate over a spherical surface |
Diagram:
graph LR
A[Poynting Vector<br>P = E × H] --> B[Time-average<br>power density]
B --> C[Integrate over sphere<br>P = ∫∫P·ds]
C --> D[Power radiated<br>P = 80π²I²l²/λ²]
- Electric field: E = (jη I₀dl/2λr) sin θ e⁻ʲᵏʳ
- Magnetic field: H = (j I₀dl/2λr) sin θ e⁻ʲᵏʳ
- Poynting vector: P = E × H* = (η|I₀|²|dl|²/8π²r²) sin² θ
- Total power: P = (η|I₀|²|dl|²/12π) = 80π²I²l²/λ²
Mnemonic: “PEHP: Poynting Explains How Power propagates”
Question 1(c) OR [7 marks]#
Define Antenna, Radiation Pattern, Directivity, Gain, FBR, Isotropic Radiator and Effective Aperture.
Answer:
Table: Key Antenna Parameters
| Parameter | Definition |
|---|---|
| Antenna | A device that converts guided electromagnetic waves to free-space waves and vice versa |
| Radiation Pattern | Graphical representation of radiation properties as a function of space coordinates |
| Directivity | Ratio of radiation intensity in a given direction to average radiation intensity |
| Gain | Ratio of radiation intensity to that of an isotropic source with same input power |
| FBR (Front-to-Back Ratio) | Ratio of power radiated in forward direction to that in backward direction |
| Isotropic Radiator | Theoretical antenna that radiates equally in all directions |
| Effective Aperture | Ratio of power received by antenna to incident power density |
Diagram:
pie
title "Antenna Performance Factors"
"Directivity" : 25
"Gain" : 25
"Effective Aperture" : 20
"Radiation Pattern" : 15
"FBR" : 15
Mnemonic: “DIAGRAM: Directivity Improves Antenna Gain, Radiation And More”
Question 2(a) [3 marks]#
Explain principle of pattern multiplication.
Answer:
Pattern multiplication states that the radiation pattern of an array equals the product of the element pattern and the array factor.
Diagram:
graph LR
A[Array Pattern] --> B["Element Pattern × Array Factor"]
B --> C[Total Field Pattern]
C --> D[Directivity Enhancement]
- Element pattern: Radiation pattern of single element
- Array factor: Pattern due to arrangement of elements
- Result: Sharper beams, higher directivity
Mnemonic: “PEAM: Pattern Equals Array times Element Method”
Question 2(b) [4 marks]#
Draw & Explain Loop antenna.
Answer:
A loop antenna is a closed-circuit antenna consisting of one or more complete turns of wire.
Diagram:
- Small loop: Circumference < λ/10, figure-8 pattern
- Large loop: Circumference ≈ λ, maximum radiation perpendicular to plane
- Applications: Direction finding, AM radio reception
- Radiation resistance: Proportional to (circumference/λ)⁴ for small loops
Mnemonic: “LOOP: Low Output, Orientation Precise”
Question 2(c) [7 marks]#
Design a Yagi-uda antenna and explain it.
Answer:
Yagi-Uda is a directional antenna with driven element, reflector, and directors.
Table: Yagi-Uda Antenna Design Guidelines
| Element | Length | Spacing from Driven Element |
|---|---|---|
| Reflector | 0.5λ × 1.05 | 0.15λ - 0.25λ |
| Driven Element | 0.5λ | Reference point |
| Director 1 | 0.5λ × 0.95 | 0.1λ - 0.15λ |
| Director 2 | 0.5λ × 0.92 | 0.2λ - 0.3λ |
| Additional Directors | Decreasing | 0.3λ - 0.4λ |
Diagram:
- Function: Reflector reflects signal, directors guide it forward
- Gain: Increases with number of directors (diminishing returns)
- Impedance: 20-30 ohms (typically matched with balun)
- Applications: TV reception, point-to-point communication
Mnemonic: “YARD: Yagi Achieves Radical Directivity”
Question 2(a) OR [3 marks]#
Compare broad fire and end fire array antenna.
Answer:
Table: Broad Side vs End Fire Array
| Parameter | Broad Side Array | End Fire Array |
|---|---|---|
| Direction of Maximum Radiation | Perpendicular to array axis | Along array axis |
| Phase Difference | 0° | 180° ± βd |
| Beam Width | Narrower | Wider |
| Directivity | Higher | Lower |
| Applications | Broadcasting | Point-to-point links |
Diagram:
graph LR
A[Array Antennas] --> B[Broad Side]
A --> C[End Fire]
B --> D[Max radiation perpendicular<br>to array axis]
C --> E[Max radiation along<br>array axis]
Mnemonic: “BEPS: Broadside Emits Perpendicularly, Sideways”
Question 2(b) OR [4 marks]#
Draw & Explain Folded dipole antenna.
Answer:
A folded dipole consists of a half-wavelength dipole with its ends folded back and connected, forming a narrow loop.
Diagram:
- Impedance: 4 times higher than standard dipole (≈300Ω)
- Bandwidth: Wider than simple dipole
- Applications: TV antennas, FM receiving antennas
- Advantage: Less susceptible to noise
Mnemonic: “FIBER: Folded Impedance Booster Enhances Reception”
Question 2(c) OR [7 marks]#
Give names of Non-resonant antennas and explain any one in detail with its radiation pattern.
Answer:
Non-resonant antennas include Rhombic, V antenna, Terminated folded dipole, Beverage, and Long-wire antennas.
Rhombic Antenna in Detail:
Diagram:
Table: Rhombic Antenna Characteristics
| Parameter | Description |
|---|---|
| Structure | Four long wires arranged in rhombus shape |
| Termination | Resistive load at far end (non-resonant) |
| Directivity | High (8-15 dB) |
| Frequency Range | Wide bandwidth (multi-octave) |
| Radiation Pattern | Unidirectional, cone-shaped |
| Applications | HF point-to-point communications |
- Advantages: High gain, broad bandwidth, simple construction
- Disadvantages: Large physical size, power loss in terminating resistor
- Pattern: Main lobe along major axis of rhombus
Mnemonic: “RHOMBIC: Reliable High-Output Multi-Band Impressive Communications”
Question 3(a) [3 marks]#
Compare radiation pattern of different resonant wire antennas.
Answer:
Table: Radiation Patterns of Resonant Wire Antennas
| Antenna Type | Pattern Shape | Directivity | Polarization |
|---|---|---|---|
| Half-Wave Dipole | Figure-8 (donut) | 2.15 dBi | Linear |
| Full-Wave Dipole | Four-lobed | 3.8 dBi | Linear |
| 3λ/2 Dipole | Six-lobed | 4.2 dBi | Linear |
| 2λ Dipole | Eight-lobed | 4.5 dBi | Linear |
Diagram:
graph TD
A[Resonant Wire Antennas] --> B[Half-Wave Dipole<br>Figure-8 Pattern]
A --> C[Full-Wave Dipole<br>Four-lobed Pattern]
A --> D[Multi-wavelength Dipole<br>Multi-lobed Pattern]
Mnemonic: “MOLD: More wavelengths create Lots of Directivity lobes”
Question 3(b) [4 marks]#
Draw V and Inverted V antenna with radiation Pattern.
Answer:
Diagram: V-Antenna
Diagram: Inverted V-Antenna
- V-Antenna: Two wires forming V-shape, bidirectional pattern
- Inverted V: Half-wave dipole with arms drooping down, omnidirectional
- Applications: Amateur radio, FM reception
- Advantages: Simple, flexible installation options
Mnemonic: “VIPS: V-shapes Improve Pattern Selectivity”
Question 3(c) [7 marks]#
Explain Morse Code and Practice Oscillator.
Answer:
Morse code is a method of transmitting text using standardized sequences of dots and dashes.
Table: Basic Morse Code Elements
| Element | Timing | Sound |
|---|---|---|
| Dot (.) | 1 unit | Short beep |
| Dash (-) | 3 units | Long beep |
| Space between elements | 1 unit | Short silence |
| Space between letters | 3 units | Medium silence |
| Space between words | 7 units | Long silence |
Diagram: Simple Morse Code Practice Oscillator
- Components: 555 timer, resistors, capacitors, key, speaker
- Operation: Key closing completes circuit, creating oscillation
- Frequency: Typically 600-800 Hz (adjustable with R2)
- Applications: Ham radio training, emergency communications
Mnemonic: “TEMPO: Timing Elements Make Perfect Oscillation”
Question 3(a) OR [3 marks]#
Draw and Explain Microstrip Patch antenna.
Answer:
A microstrip patch antenna consists of a metal patch on a grounded substrate.
Diagram:
- Structure: Metal patch on dielectric substrate with ground plane
- Advantages: Low profile, lightweight, easy fabrication, conformable
- Disadvantages: Narrow bandwidth, low efficiency, low power handling
- Applications: Mobile devices, RFID, satellite communications
Mnemonic: “MAPS: Microstrip Antenna Patches are Simple”
Question 3(b) OR [4 marks]#
Draw and Explain Horn antenna.
Answer:
A horn antenna is a waveguide with flared open end that directs radio waves in a beam.
Diagram:
- Types: E-plane, H-plane, Pyramidal, Conical
- Frequency range: Microwave (1-20 GHz)
- Advantages: High gain, wide bandwidth, low VSWR
- Applications: Satellite communications, radar, radio astronomy
Mnemonic: “HEWB: Horns Enhance Waveguide Beamwidth”
Question 3(c) OR [7 marks]#
List different feed system for Parabolic reflector antenna and explain any one.
Answer:
Table: Parabolic Reflector Feed Systems
| Feed System | Position | Characteristics |
|---|---|---|
| Front Feed | At focus, in front of dish | Simple, some blockage |
| Cassegrain | Secondary reflector with feed at center of dish | Reduced noise, compact |
| Gregorian | Secondary concave reflector | Better gain, larger size |
| Offset Feed | Feed offset from main axis | No blockage, asymmetric |
| Waveguide Feed | Direct waveguide at focus | Simple, limited flexibility |
Front Feed System (Detailed):
Diagram:
graph LR
A[Parabolic Reflector] --- B[Focal Point]
B --- C[Feed Horn]
C --- D[Waveguide/Coax]
D --- E[Receiver/Transmitter]
- Operation: Feed placed at focal point, illuminates reflector
- Advantages: Simple design, easy alignment, maximum efficiency
- Disadvantages: Feed and support structure block part of aperture
- Applications: Satellite dishes, radio telescopes, radar
Mnemonic: “FACTS: Focused Aperture Captures Transmitted Signals”
Question 4(a) [3 marks]#
Explain working principle of HAM radio.
Answer:
HAM radio (Amateur Radio) operates on designated frequency bands for non-commercial communications.
Diagram:
graph LR
A[Transmitter] --> B[Antenna]
B --> C[Propagation Medium]
C --> D[Receiver Antenna]
D --> E[Receiver]
- Operation: Transmitter generates RF signal, antenna radiates signal
- Frequency bands: HF (3-30 MHz), VHF (30-300 MHz), UHF (300-3000 MHz)
- Modes: AM, FM, SSB, CW (Morse), digital modes
- License: Required for legal operation (levels based on skills)
Mnemonic: “TEAM: Transmission Enables Amateur Messages”
Question 4(b) [4 marks]#
Explain Duct Propagation.
Answer:
Duct propagation occurs when radio waves are trapped within atmospheric layers with varying refractive indices.
Diagram:
- Formation: Temperature inversion creates refractive index gradient
- Frequency range: VHF, UHF, microwave frequencies
- Advantages: Extended communication range (beyond horizon)
- Occurrence: Common over oceans, varies with weather conditions
Mnemonic: “TRIP: Trapped Rays In atmospheric Paths”
Question 4(c) [7 marks]#
Explain Tropospheric Scattered Propagation in detail.
Answer:
Tropospheric scatter uses the scattering properties of the troposphere to enable beyond-horizon communications.
Table: Tropospheric Scatter Characteristics
| Parameter | Description |
|---|---|
| Mechanism | Forward scattering of radio waves by tropospheric irregularities |
| Frequency Range | 300 MHz to 10 GHz (UHF/SHF) |
| Range | 100-800 km |
| Path Loss | High (requires high-power transmitters) |
| Reliability | Affected by weather conditions |
Diagram:
graph LR
A[Transmitter] --> B[High Gain Antenna]
B --> C[Scattering Volume<br>in Troposphere]
C --> D[Receiving Antenna]
D --> E[Receiver]
F[Factors] --> G[Weather]
F --> H[Frequency]
F --> I[Antenna Size]
- Mechanism: Signal scattered by refractive index irregularities
- Equipment: High-power transmitters, large antennas, sensitive receivers
- Applications: Military, backup communications, remote areas
- Advantages: Beyond line-of-sight, relatively stable
Mnemonic: “STARS: Scatter Tropospheric Allows Range beyond Sight”
Question 4(a) OR [3 marks]#
Draw turnstile and super turnstile antenna.
Answer:
Diagram: Turnstile Antenna
Diagram: Super Turnstile (Batwing) Antenna
- Turnstile: Two dipoles at right angles, circular polarization
- Super turnstile: Multiple elements for increased bandwidth
- Applications: TV broadcasting, FM broadcasting, satellite communications
- Advantage: Omnidirectional horizontal pattern
Mnemonic: “TACO: Turnstile Antennas Create Omnidirectional patterns”
Question 4(b) OR [4 marks]#
Give full form of MUF, LUF and OUF.
Answer:
Table: Ionospheric Propagation Parameters
| Abbreviation | Full Form | Description |
|---|---|---|
| MUF | Maximum Usable Frequency | Highest frequency that can be reflected by ionosphere |
| LUF | Lowest Usable Frequency | Lowest frequency providing adequate signal-to-noise ratio |
| OUF | Optimum Usable Frequency | Best working frequency (85% of MUF) |
Diagram:
graph TD
A[Ionospheric Frequencies] --> B[MUF]
A --> C[LUF]
A --> D[OUF]
B --> E[Highest frequency<br>that returns to Earth]
C --> F[Lowest frequency<br>with adequate SNR]
D --> G[Best working frequency<br>85% of MUF]
Mnemonic: “MLO: Maximum and Lowest determine Optimum”
Question 4(c) OR [7 marks]#
Explain virtual height, critical frequency and skip distance in detail.
Answer:
Table: Key Ionospheric Propagation Parameters
| Parameter | Definition | Significance |
|---|---|---|
| Virtual Height | Apparent reflection height assuming straight-line propagation | Determines maximum communication range |
| Critical Frequency | Maximum frequency reflected at vertical incidence | Indicates ionization density |
| Skip Distance | Minimum distance where ionospheric signals can be received | Creates “skip zones” with no reception |
Diagram:
- Virtual height: Typically 300-400 km for F layer, varies with time/season
- Critical frequency: Usually 5-10 MHz for F2 layer, depends on solar activity
- Skip distance: Given by D = 2h tan θ, where h is virtual height and θ is incidence angle
Mnemonic: “VCS: Virtual height Controls Skip distance”
Question 5(a) [3 marks]#
With neat figure show different Ionosphere layers.
Answer:
Diagram: Ionospheric Layers
- D Layer: 60-90 km, absorbs HF waves, disappears at night
- E Layer: 90-150 km, reflects MF/lower HF, weakens at night
- F1 Layer: 150-220 km, present in daytime only
- F2 Layer: 220-400 km, main reflection layer, present day/night
Mnemonic: “DEAF: Down to up - D, E, And F layers”
Question 5(b) [4 marks]#
Give names of different types of satellite communication systems and compare it.
Answer:
Table: Satellite Communication Systems
| System Type | Frequency Bands | Applications | Characteristics |
|---|---|---|---|
| Telecommunication | C, Ku, Ka bands | Phone, data, internet | Global coverage, high capacity |
| Broadcasting | Ku, C bands | TV, radio transmission | High power, wide coverage |
| Data Communication | L, S, Ka bands | IoT, VSAT, M2M | Low to medium data rates |
| Military | X, EHF bands | Secure communications | Encrypted, jam-resistant |
| Navigation | L band | GPS, GLONASS, Galileo | Precise timing, positioning |
Diagram:
pie
title "Satellite Communication Systems"
"Telecommunication" : 30
"Broadcasting" : 25
"Data Communication" : 20
"Military" : 15
"Navigation" : 10
Mnemonic: “TBDMN: Telecom, Broadcasting, Data, Military, Navigation”
Question 5(c) [7 marks]#
Draw and explain DTH receiver system.
Answer:
DTH (Direct-to-Home) system delivers television programming directly to viewers via satellite.
Diagram:
Table: DTH System Components
| Component | Function | Specifications |
|---|---|---|
| Dish Antenna | Collects satellite signals | 45-120 cm diameter |
| LNB (Low Noise Block) | Converts high frequency to lower IF | Noise figure: 0.3-1.0 dB |
| Coaxial Cable | Carries IF signal to receiver | RG-6 type, 75 ohm |
| Set-top Box | Demodulates/decodes signals | MPEG-2/4 decoder |
| TV Set | Displays programming | HDMI/Component input |
- Frequency: Ku-band (10.7-12.75 GHz) or C-band (3.7-4.2 GHz)
- Modulation: QPSK or 8PSK digital modulation
- Signal processing: Digital compression (MPEG-2/4)
- Features: EPG (Electronic Program Guide), PVR (recording)
Mnemonic: “DOCS: Dish Obtains, Converts and Shows signals”
Question 5(a) OR [3 marks]#
What is the Need of Smart Antennas? Write its applications.
Answer:
Smart antennas use adaptive signal processing to dynamically optimize radiation patterns.
Needs:
- Increased capacity in congested networks
- Improved signal quality and coverage
- Reduced interference and multipath fading
- Enhanced spectral efficiency
Diagram:
graph TD
A[Smart Antenna] --> B[Adaptive<br>Beamforming]
A --> C[Spatial<br>Multiplexing]
A --> D[Interference<br>Suppression]
Applications:
- Mobile communication networks (4G/5G)
- MIMO systems for high data rates
- Radar systems with enhanced target detection
- Wireless LANs with improved coverage
Mnemonic: “SAFE: Smart Antennas For Efficiency”
Question 5(b) OR [4 marks]#
Explain Kepler’s 3rd law.
Answer:
Kepler’s 3rd law relates the orbital period of a satellite to its semi-major axis.
Formula: T² = (4π²/GM) × a³
Where:
- T = orbital period
- a = semi-major axis
- G = gravitational constant
- M = mass of central body
Diagram:
graph LR
A[Kepler's 3rd Law] --> B["T² ∝ a³"]
B --> C[T = orbital period]
B --> D[a = semi-major axis]
E[Applications] --> F[Satellite orbit determination]
E --> G[Spacecraft mission planning]
- Meaning: Larger orbits have longer periods
- Application: Determines satellite orbit characteristics
- Geostationary orbit: Period = 24 hours, altitude ≈ 35,786 km
Mnemonic: “CAP: Cube of Axis equals Period squared”
Question 5(c) OR [7 marks]#
Identify the different types of Antennas for Terrestrial Mobile communication and explain in detail.
Answer:
Table: Terrestrial Mobile Communication Antennas
| Antenna Type | Typical Gain | Polarization | Applications |
|---|---|---|---|
| Base Station Antennas | 10-18 dBi | Vertical/Dual | Cell towers, fixed infrastructure |
| Mobile Station Antennas | 0-3 dBi | Vertical | Smartphones, vehicles, portable devices |
| Repeater Antennas | 5-10 dBi | Circular/Dual | Signal boosting, coverage extension |
| Diversity Antennas | Variable | Multiple | Multipath mitigation, MIMO systems |
Base Station Antennas (Detailed):
Diagram:
- Types: Panel arrays, collinear arrays, sector antennas
- Characteristics:
- High gain (10-18 dBi)
- Directional radiation pattern (60°-120° sectors)
- Downtilt capability (electrical/mechanical)
- Multiple-band operation
- Advanced features:
- Multiple-input multiple-output (MIMO)
- Remote electrical tilt (RET)
- Integrated diplexers/triplexers
Mobile Station Antennas:
- Compact size (internal/external)
- Omnidirectional pattern
- Multiple band support (700-2600 MHz)
- Implementations: PIFA, helical, monopole designs
Mnemonic: “BEST: Base-stations Employ Sector Technology”