Question 1(a) [3 marks]#
Define: (1) Directivity, (2) Gain, and (3) HPBW
Answer:
Table: Antenna Parameters Definitions
| Parameter | Definition |
|---|---|
| Directivity | The ratio of radiation intensity in a given direction to the average radiation intensity in all directions, |
| Gain | The ratio of power radiated in a specific direction to the power that would be radiated by an isotropic antenna with the same input power |
| HPBW (Half Power Beam Width) | The angular width of the main lobe where the power falls to half (-3dB) of its maximum value |
Mnemonic: “DGH: Direction Gets Higher power with narrow beam”
Question 1(b) [4 marks]#
List the properties of electromagnetic waves
Answer:
Table: Properties of Electromagnetic Waves
| Property | Description |
|---|---|
| Transverse nature | Electric and magnetic fields are perpendicular to each other and to direction of propagation |
| Velocity | Travel at speed of light (3×10⁸ m/s) in free space |
| Frequency range | Vary from few Hz to several THz |
| Energy transport | Carry energy from one point to another without need of medium |
| Reflection | Can be reflected from conducting surfaces |
| Refraction | Change direction when passing between different media |
| Diffraction | Can bend around obstacles |
| Polarization | The orientation of electric field vector |
Mnemonic: “TVFERRDP: Travel Very Fast, Energy Reflects Refracts Diffracts Polarizes”
Question 1(c) [7 marks]#
Explain physical concept of generation of Electromagnetic wave
Answer:
Diagram: Generation of Electromagnetic Wave
graph LR
A[Oscillating Electric Charge] --> B[Time-varying Electric Field]
B --> C[Time-varying Magnetic Field]
C --> D[Time-varying Electric Field]
D --> E[Self-sustaining EM Wave]
style A fill:#f9f,stroke:#333
style E fill:#bbf,stroke:#333
Process of EM Wave Generation:
- Accelerating charge: When electric charge accelerates, it produces time-varying electric field
- Changing electric field: This creates a time-varying magnetic field
- Changing magnetic field: In turn creates a time-varying electric field
- Self-propagation: This mutual creation of fields results in self-propagating wave
- Energy transfer: EM waves transfer energy from transmitter to receiver
Maxwell’s Equations: These four equations mathematically describe the generation and propagation of EM waves:
- Electric field from charges (Gauss’s law)
- No magnetic monopoles exist
- Electric fields from changing magnetic fields (Faraday’s law)
- Magnetic fields from currents and changing electric fields (Ampere’s law)
Mnemonic: “CASES: Charges Accelerate, Self-sustaining Electric-Magnetic fields”
Question 1(c) OR [7 marks]#
Explain how electromagnetic field radiated from a center fed dipole
Answer:
Diagram: Radiation from Center-Fed Dipole
graph LR
A[RF Generator] --> B[Center-Fed Dipole]
B --> C{Current Flow}
C --> D[Electric Field]
C --> E[Magnetic Field]
D --> F[Radiation Pattern]
E --> F
style A fill:#f9f,stroke:#333
style F fill:#bbf,stroke:#333
Radiation Process:
| Stage | Process |
|---|---|
| 1. Current excitation | RF signal applied at center of dipole creates alternating current |
| 2. Current distribution | Sinusoidal current distribution forms along dipole, maximum at center, zero at ends |
| 3. Electric field | Oscillating charges create time-varying electric field perpendicular to dipole |
| 4. Magnetic field | Current flow creates magnetic field perpendicular to both dipole and electric field |
| 5. Near field | Complex field pattern forms close to antenna (< λ/2π) |
| 6. Far field | At distances > 2λ, radiation stabilizes to form distinctive pattern with main and side lobes |
Characteristics:
- Maximum radiation: Perpendicular to dipole axis
- Null radiation: Along dipole axis
- Omnidirectional: In azimuth plane (perpendicular to dipole)
- Polarization: Same as orientation of dipole
Mnemonic: “COME-FR: Current Oscillates, Making Electric-magnetic Fields that Radiate”
Question 2(a) [3 marks]#
Differentiate the resonant and non-resonant antennas
Answer:
Table: Resonant vs Non-Resonant Antennas
| Parameter | Resonant Antennas | Non-Resonant Antennas |
|---|---|---|
| Physical length | Multiple of λ/2 (usually λ/2 or λ) | Not related to wavelength (typically > λ) |
| Standing waves | Strong standing waves present | Minimal standing waves |
| Current distribution | Sinusoidal with maximum at center | Traveling wave with uniform amplitude |
| Input impedance | Resistive (at resonant frequency) | Complex (resistive + reactive) |
| Bandwidth | Narrow bandwidth | Wide bandwidth |
| Examples | Half-wave dipole, folded dipole | Rhombic antenna, traveling wave antenna |
Mnemonic: “SIN-CIB: Size, Impedance, Narrow vs Complex, Impedance, Broad”
Question 2(b) [4 marks]#
Explain Yagi antenna and discuss its radiation characteristics
Answer:
Diagram: Yagi-Uda Antenna
Yagi Antenna Components:
- Driven element: Half-wave dipole connected to transmission line
- Reflector: Slightly longer than driven element, placed behind it
- Directors: Multiple elements shorter than driven element, placed in front
Radiation Characteristics:
- Directivity: High (7-12 dBi) with more directors
- Radiation pattern: Unidirectional, narrow beam along director axis
- Front-to-back ratio: 15-20 dB (good rejection of signals from rear)
- Bandwidth: Moderate (around 5% of center frequency)
- Gain: Increases with number of directors (typically 3-20 dBi)
Mnemonic: “DRDU: Directors Radiate, Driven powers, Unidirectional beam”
Question 2(c) [7 marks]#
Describe radiation characteristics of resonant wire antennas and draw the current distribution of λ/2, 3λ/2 and 5λ/2 antenna
Answer:
Diagram: Current Distribution on Resonant Wire Antennas
Radiation Characteristics of Resonant Wire Antennas:
| Characteristic | Description |
|---|---|
| Current distribution | Sinusoidal, with maximum at center for λ/2, additional maxima for longer antennas |
| Input impedance | Approximately 73Ω for λ/2, varies for longer antennas |
| Radiation pattern | Figure-8 pattern (λ/2), more complex lobes for longer antennas |
| Directivity | 2.15 dBi for λ/2, increases with length but with multiple lobes |
| Polarization | Linear, parallel to wire orientation |
| Efficiency | High for properly constructed antennas |
Key Points:
- λ/2 antenna has single current maximum at center
- 3λ/2 antenna has three half-cycles of current distribution
- 5λ/2 antenna has five half-cycles of current distribution
- More half-wavelengths create more radiation lobes
- Feed point is typically at current maximum for best impedance match
Mnemonic: “SIMPLE: Sinusoidal In Middle Produces Lobes Efficiently”
Question 2(a) OR [3 marks]#
Differentiate the broad side and end fire array antennas
Answer:
Table: Broadside vs End Fire Array Antennas
| Parameter | Broadside Array | End Fire Array |
|---|---|---|
| Direction of maximum radiation | Perpendicular to the array axis | Along the array axis |
| Phase difference | 0° (in-phase) | 180° or progressive phase |
| Element spacing | Typically λ/2 | Typically λ/4 to λ/2 |
| Radiation pattern | Narrow in plane containing array axis | Narrow in plane perpendicular to array elements |
| Directivity | High, increases with number of elements | High, increases with number of elements |
| Applications | Fixed point-to-point links | Direction finding, radar |
Mnemonic: “BEPODS: Broadside-End, Perpendicular-Or-Direction, Spacing”
Question 2(b) OR [4 marks]#
Explain loop antenna and discuss its radiation characteristics
Answer:
Diagram: Loop Antenna Types
graph TD
A[Loop Antenna] --> B[Small Loop<br>Circumference < λ/10]
A --> C[Large Loop<br>Circumference ≈ λ]
style A fill:#f9f,stroke:#333
style B fill:#bbf,stroke:#333
style C fill:#bbf,stroke:#333
Loop Antenna Characteristics:
| Parameter | Small Loop | Large Loop |
|---|---|---|
| Current distribution | Uniform around loop | Varies around circumference |
| Radiation pattern | Figure-8 (perpendicular to loop plane) | More complex with multiple lobes |
| Directivity | Low (1.5 dBi) | Higher (3-4 dBi) |
| Polarization | Magnetic field perpendicular to loop | Electric field in plane of loop |
| Input impedance | Very low (< 10Ω) | Higher (50-200Ω) |
| Applications | Direction finding, AM receivers | HF communications, RFID |
Mnemonic: “SCALED: Size Changes Antenna’s Lobes, Efficiency, and Direction”
Question 2(c) OR [7 marks]#
Describe radiation characteristics of non resonant wire antennas and draw the radiation pattern of λ/2, 3λ/2 and 5λ/2 antenna
Answer:
Diagram: Radiation Patterns of Wire Antennas
Non-Resonant Wire Antenna Characteristics:
| Characteristic | Description |
|---|---|
| Current distribution | Traveling waves with minimal standing waves |
| Termination | Usually terminated with resistive load to prevent reflections |
| Bandwidth | Wide bandwidth operation |
| Input impedance | More constant across frequency range |
| Radiation pattern | λ/2: Single main lobe on each side 3λ/2: Three main lobes on each side 5λ/2: Five main lobes on each side |
| Directivity | Increases with length but divided among multiple lobes |
| Efficiency | Lower than resonant antennas due to resistive termination |
Key Points:
- Non-resonant antennas use traveling waves instead of standing waves
- Rhombic antenna is a common non-resonant antenna
- λ/2 pattern has 2 main lobes (figure-8 pattern)
- 3λ/2 pattern has 6 main lobes (3 on each side)
- 5λ/2 pattern has 10 main lobes (5 on each side)
- More lobes appear as length increases
- Main beam angle changes with frequency
Mnemonic: “TRIBE-WL: Traveling Resistance Improves Bandwidth, Efficiency Worse, Lobes multiply”
Question 3(a) [3 marks]#
Write short note on micro strip (patch) antenna
Answer:
Diagram: Microstrip Patch Antenna
Microstrip Patch Antenna:
- Structure: Metal patch on dielectric substrate with ground plane
- Size: Typically λ/2 × λ/2 or λ/2 × λ/4
- Feed methods: Microstrip line, coaxial probe, aperture coupling
- Radiation: From fringing fields at patch edges
- Polarization: Linear or circular depending on patch shape
- Bandwidth: Narrow (3-5% of center frequency)
- Applications: Mobile devices, satellites, aircraft, RFID
Mnemonic: “SLIM-PCB: Small, Lightweight, Integrable Microwave Printed Circuit Board”
Question 3(b) [4 marks]#
Explain helical antenna and discuss its radiation characteristics
Answer:
Diagram: Helical Antenna
Helical Antenna Characteristics:
| Parameter | Normal Mode | Axial Mode |
|---|---|---|
| Helix circumference | Small (< λ/π) | About λ |
| Radiation pattern | Omnidirectional (like dipole) | Directional (end-fire) |
| Polarization | Linear, perpendicular to helix axis | Circular (RHCP or LHCP) |
| Input impedance | High (120-200Ω) | 100-200Ω |
| Bandwidth | Narrow | Wide (up to 70%) |
| Applications | Mobile phones, FM radio | Satellite comms, space telemetry |
Key Parameters:
- Diameter (D)
- Spacing between turns (S)
- Number of turns (N)
- Pitch angle (α)
Mnemonic: “NASA-CP: Normal Axial Spacing Affects Circular Polarization”
Question 3(c) [7 marks]#
Explain horn antenna and discuss its radiation characteristics
Answer:
Diagram: Types of Horn Antennas
graph TD
A[Horn Antenna] --> B[E-plane Horn]
A --> C[H-plane Horn]
A --> D[Pyramidal Horn]
A --> E[Conical Horn]
style A fill:#f9f,stroke:#333
style B fill:#bbf,stroke:#333
style C fill:#bbf,stroke:#333
style D fill:#bbf,stroke:#333
style E fill:#bbf,stroke:#333
Diagram: Horn Antenna Structure
Horn Antenna Characteristics:
| Characteristic | Description |
|---|---|
| Operating principle | Gradual transition from waveguide to free space |
| Frequency range | Microwave and mm-wave (1-300 GHz) |
| Directivity | Medium to high (10-20 dBi) |
| Radiation pattern | Directional with main lobe in forward direction |
| Beamwidth | E-plane: 40-50°, H-plane: 40-50°, Pyramidal: depends on dimensions |
| Polarization | Linear (matches waveguide) |
| Bandwidth | Very wide (>100%) |
| Efficiency | Very high (>90%) |
| Applications | Radar, satellite communications, EMC testing, radio astronomy |
Types of Horn Antennas:
- E-plane horn: Flared in electric field direction
- H-plane horn: Flared in magnetic field direction
- Pyramidal horn: Flared in both planes
- Conical horn: Circular waveguide with conical flare
Mnemonic: “POWER-HF: Pyramidal Or Waveguide Extended, Radiates High Frequencies”
Question 3(a) OR [3 marks]#
Write short note on slot antenna
Answer:
Diagram: Slot Antenna
Slot Antenna:
- Structure: Narrow slot cut in conductive sheet/plane
- Size: Typically λ/2 long for resonance
- Feed method: Across the slot at center or offset
- Radiation pattern: Similar to dipole but rotated 90° (Babinet’s principle)
- Polarization: Linear, perpendicular to slot length
- Impedance: High (several hundred ohms)
- Applications: Aircraft, satellites, base stations
Key Points:
- Complementary to dipole (Babinet’s principle)
- Radiates equally from both sides of plane
- Can be flush-mounted (advantage for aerodynamics)
- Can be covered with dielectric without affecting performance
Mnemonic: “SCRAP: Slot Cut Radiates Alternating Polarization”
Question 3(b) OR [4 marks]#
Explain parabolic reflector antenna and discuss its radiation characteristics
Answer:
Diagram: Parabolic Reflector Antenna
Parabolic Reflector Antenna Characteristics:
| Characteristic | Description |
|---|---|
| Operating principle | Focuses parallel incoming waves to focal point (receiving) or collimates waves from focal point (transmitting) |
| Frequency range | From UHF to millimeter waves (300 MHz - 300 GHz) |
| Directivity | Very high (30-40 dBi for large dishes) |
| Radiation pattern | Highly directional, narrow main beam |
| Beamwidth | Inversely proportional to diameter (θ ≈ 70λ/D degrees) |
| Feed types | Prime focus, Cassegrain, Gregorian, offset |
| Efficiency | 50-70% depending on feed design and blockage |
| Applications | Satellite communications, radio astronomy, radar, microwave links |
Key Parameters:
- Diameter (D)
- Focal length (f)
- f/D ratio (typically 0.3-0.6)
Mnemonic: “FIND-SHF: Focused, Intense Narrow Directivity for Super High Frequencies”
Question 3(c) OR [7 marks]#
Describe V and inverted V antenna
Answer:
Diagram: V and Inverted V Antennas
V Antenna Characteristics:
| Characteristic | Description |
|---|---|
| Construction | Two equal length wires arranged in V-shape |
| Angle between arms | 10-90° (affects directivity) |
| Length of each arm | Typically multiple wavelengths (1-6λ) |
| Radiation pattern | Bidirectional for larger angles, unidirectional for smaller angles |
| Directivity | 3-15 dBi (increases with arm length and decreases with angle) |
| Input impedance | 300-900Ω (depends on included angle) |
| Applications | HF long-distance communications, shortwave broadcasting |
Inverted V Antenna Characteristics:
| Characteristic | Description |
|---|---|
| Construction | Similar to dipole but bent down in V-shape |
| Angle between arms | 90-120° typically |
| Length of each arm | λ/4 each (total λ/2) |
| Radiation pattern | Omnidirectional (slightly more overhead than dipole) |
| Input impedance | Lower than dipole (typically 50Ω) |
| Height requirement | Only center needs to be high |
| Applications | Amateur radio, general HF communications |
Key Differences:
- V antenna is horizontally oriented, Inverted V is vertically oriented with center up
- V antenna usually has longer arms for directivity
- Inverted V requires only one support point (center)
- V antenna has higher directivity, Inverted V is more omnidirectional
Mnemonic: “VOVO: V Outward (radiation), V One-support (inverted)”
Question 4(a) [3 marks]#
Define: (1) Reflection, (2) Refraction and (3) Diffraction
Answer:
Table: Wave Phenomena Definitions
| Phenomenon | Definition |
|---|---|
| Reflection | The bouncing back of electromagnetic waves when they strike a boundary between two different media without penetrating the second medium |
| Refraction | The bending of electromagnetic waves when they pass from one medium to another due to change in wave velocity |
| Diffraction | The bending of electromagnetic waves around obstacles or through openings, allowing waves to propagate into shadowed regions |
Mnemonic: “RRD: Rays Rebound, Redirect, Disperse”
Question 4(b) [4 marks]#
List HAM radio application for communication
Answer:
Table: HAM Radio Applications for Communication
| Application Category | Specific Applications |
|---|---|
| Emergency communications | Disaster relief, emergency response, weather reporting |
| Public service | Community events, search and rescue, traffic monitoring |
| Technical experimentation | Antenna design, propagation studies, digital modes testing |
| International goodwill | DX communication, contesting, international friendship |
| Personal recreation | Casual conversations, hobby groups, radio clubs |
| Educational outreach | School programs, STEM activities, training new operators |
| Space communication | Satellite operation, ISS contact, EME (moon bounce) |
| Digital communication | APRS, packet radio, FT8, RTTY, PSK31 |
Mnemonic: “EPTIPS-D: Emergency, Public, Technical, International, Personal, Space, Digital”
Question 4(c) [7 marks]#
Explain ionosphere’s layers and sky wave propagation
Answer:
Diagram: Ionospheric Layers and Sky Wave Propagation
graph TD
A[Transmitter] --> B[Ionosphere]
B --> C[F2 Layer<br>250-450 km]
B --> D[F1 Layer<br>170-220 km]
B --> E[E Layer<br>90-120 km]
B --> F[D Layer<br>60-90 km]
C --> G[Receiver]
style A fill:#f9f,stroke:#333
style G fill:#bbf,stroke:#333
Ionospheric Layers:
| Layer | Altitude | Characteristics | Effect on Radio Waves |
|---|---|---|---|
| D Layer | 60-90 km | Low ionization, exists only during daylight | Absorbs LF/MF signals, minimal refraction |
| E Layer | 90-120 km | Medium ionization, stronger during day | Refracts HF waves up to 5 MHz |
| F1 Layer | 170-220 km | Present only during day, merges with F2 at night | Refracts higher HF frequencies |
| F2 Layer | 250-450 km | Highest ionization, present day and night | Main layer for long-distance HF communication |
Sky Wave Propagation Parameters:
| Parameter | Definition |
|---|---|
| Virtual Height | Apparent height where reflection seems to occur (higher than actual due to gradual refraction) |
| Critical Frequency | Maximum frequency that can be reflected when transmitted vertically |
| Maximum Usable Frequency (MUF) | Highest frequency that can be used for communication between two points |
| Skip Distance | Minimum distance from transmitter where sky waves return to Earth |
| Lowest Usable Frequency (LUF) | Minimum frequency that provides reliable communication (below which D-layer absorption is too high) |
| Optimum Working Frequency (OWF) | Typically 85% of MUF, provides most reliable communication |
Mnemonic: “DEFMSL: During day, Every Frequency Makes Somewhat Longer paths”
Question 4(a) OR [3 marks]#
Define: (1) MUF, (2) LUF and (3) Skip distance
Answer:
Table: Sky Wave Propagation Terms
| Term | Definition |
|---|---|
| MUF (Maximum Usable Frequency) | The highest frequency that can be used for reliable communication between two specific points via ionospheric reflection |
| LUF (Lowest Usable Frequency) | The minimum frequency that provides adequate signal strength for reliable communication despite D-layer absorption |
| Skip Distance | The minimum distance from a transmitter at which a sky wave of a specific frequency returns to Earth |
Mnemonic: “MLS: Maximum frequency Leaps, Lowest frequency Seeps, Skip distance Spans”
Question 4(b) OR [4 marks]#
List HAM radio digital modes of communication
Answer:
Table: HAM Radio Digital Modes
| Digital Mode | Description | Typical Frequency Bands |
|---|---|---|
| FT8 | Low power, narrow bandwidth, automated exchange | HF bands (especially 20m, 40m, 80m) |
| PSK31 | Phase Shift Keying, keyboard-to-keyboard | HF bands (especially 20m, 40m) |
| RTTY | Radio Teletype, oldest digital mode | HF bands |
| APRS | Automatic Packet Reporting System, position reporting | VHF (typically 144.39 MHz in US) |
| SSTV | Slow Scan Television, image transmission | HF bands (especially 20m) |
| JT65/JT9 | Weak signal modes for EME and DX | HF and VHF bands |
| WINLINK | Email over radio | HF and VHF bands |
| DMR | Digital Mobile Radio, voice digital mode | VHF and UHF bands |
Mnemonic: “PRAW-JDW: PSK, RTTY, APRS, WINLINK, JT65, DMR”
Question 4(c) OR [7 marks]#
Explain space wave propagation
Answer:
Diagram: Space Wave Propagation
Space Wave Propagation:
Space wave propagation refers to radio waves that travel through the troposphere (lower atmosphere) rather than via ionospheric reflection. It includes:
| Component | Description |
|---|---|
| Direct wave | Travels in straight line from transmitter to receiver (line-of-sight) |
| Ground-reflected wave | Reflects off Earth’s surface before reaching receiver |
| Surface wave | Follows Earth’s curvature due to diffraction |
Types of Space Wave Propagation:
Tropospheric Scatter Propagation:
- Mechanism: Signal scattering by irregularities in troposphere
- Frequency range: VHF, UHF, SHF (100 MHz - 10 GHz)
- Distance: 100-800 km (beyond horizon)
- Characteristics: High power required, fading common, reliable
- Applications: Military communications, backup links
Duct Propagation:
- Mechanism: Trapping of waves in atmospheric ducts (layers with abnormal refractive index)
- Frequency range: VHF, UHF, microwave
- Distance: Up to 2000 km (far beyond horizon)
- Characteristics: Seasonal/weather dependent, mainly over water
- Applications: Maritime communications, coastal radar
Factors Affecting Space Wave Propagation:
- Height of antennas: Higher antennas increase range
- Frequency: Higher frequencies experience less diffraction
- Terrain: Obstacles block signals (Fresnel zone clearance needed)
- Weather: Temperature inversions, humidity affect ducting
- Earth’s curvature: Limits line-of-sight distance
Mnemonic: “DRIFT-SD: Direct Routes, Irregular Formations of Troposphere, Scatter and Ducts”
Question 5(a) [3 marks]#
Define: (1) Beam area (2) Beam efficiency, and (3) Effective aperture
Answer:
Table: Antenna Beam Parameters
| Parameter | Definition |
|---|---|
| Beam Area | The solid angle through which all of the power radiated by the antenna would pass if the radiation intensity was constant at its maximum value |
| Beam Efficiency | The ratio of power radiated in the main beam to the total power radiated by the antenna |
| Effective Aperture | The ratio of power received by the antenna to the power density of the incident wave |
Mnemonic: “BEA: Beam area Encloses, efficiency Excludes sidelobes, Aperture Extracts power”
Question 5(b) [4 marks]#
Describe need of smart antenna
Answer:
Diagram: Smart Antenna System
graph LR
A[Antenna Array] --> B[Signal Processing]
B --> C[Adaptive Algorithm]
C --> D[Beamforming]
D --> E[Interference Reduction]
D --> F[Coverage Enhancement]
D --> G[Capacity Increase]
style A fill:#f9f,stroke:#333
style G fill:#bbf,stroke:#333
Need for Smart Antennas:
| Need | Description |
|---|---|
| Spectrum efficiency | Reuse frequencies more effectively in same geographic area |
| Capacity enhancement | Support more users in same bandwidth through spatial separation |
| Coverage extension | Increase range by focusing energy in desired directions |
| Interference reduction | Minimize effects of co-channel interference and jammers |
| Energy efficiency | Reduce transmitted power by focusing energy only where needed |
| Multipath mitigation | Reduce fading by selecting optimal signal paths |
| Location services | Enable direction finding and positioning applications |
| Signal quality | Improve SNR through spatial filtering |
Mnemonic: “SLIM-ACES: Spectrum efficiency, Location services, Interference reduction, Multipath mitigation, Adaptive beams, Capacity, Energy, Signal quality”
Question 5(c) [7 marks]#
Draw the DTH Receiver indoor and outdoor black diagram and discuss its functions
Answer:
Diagram: DTH Receiver System Block Diagram
DTH Receiver System Components and Functions:
Outdoor Unit Components:
| Component | Function |
|---|---|
| Satellite Dish | Collects and reflects weak satellite signals to focal point |
| LNB (Low Noise Block) | Receives signals from dish, amplifies them with minimal noise addition, and converts high frequency (10-12 GHz) to lower IF frequency (950-2150 MHz) |
Indoor Unit Components:
| Component | Function |
|---|---|
| Tuner/Demodulator | Selects desired channel frequency, demodulates signal to extract digital data stream |
| MPEG-2/4 Decoder | Decodes compressed video/audio signals into viewable/audible content |
| Conditional Access Module | Provides security and decryption for subscribed channels |
| System Controller/CPU | Manages overall operation, processes user commands, updates software |
| User Interface | Provides on-screen display, receives remote control inputs |
Signal Flow Process:
- Satellite dish collects signals and focuses them to LNB
- LNB amplifies, filters and converts signals to lower frequency
- Coaxial cable carries IF signals to indoor unit
- Tuner selects channel and demodulates signal
- Conditional access module decrypts authorized content
- MPEG decoder converts digital stream to audio/video
- Output sent to television for viewing
Mnemonic: “SALT-DCU: Satellite dish And LNB Transmit, Demodulator Converts and Unscrambles”
Question 5(a) OR [3 marks]#
Define: (1) Antenna, (2) Folded dipole, and (3) Antenna array
Answer:
Table: Antenna Definitions
| Term | Definition |
|---|---|
| Antenna | A device that converts electrical signals into electromagnetic waves for transmission or electromagnetic waves into electrical signals for reception |
| Folded Dipole | A dipole antenna modified by adding a second conductor connected at both ends to the first, forming a narrow loop with feed point at the bottom center |
| Antenna Array | A system of multiple antenna elements arranged in a specific geometric pattern to achieve desired radiation characteristics |
Mnemonic: “AFD: Antenna Feeds, Folded Doubles impedance, Directivity increases with Arrays”
Question 5(b) OR [4 marks]#
Describe application of smart antenna
Answer:
Table: Smart Antenna Applications
| Application Area | Specific Applications |
|---|---|
| Mobile Communications | Base stations for 4G/5G networks, capacity enhancement, coverage improvement |
| Wi-Fi Systems | MIMO routers, extended range access points, interference mitigation in dense deployments |
| Radar Systems | Phased array radars, target tracking, electronic warfare, weather radars |
| Satellite Communications | Adaptive beamforming, tracking earth stations, interference rejection |
| Military/Defense | Jammers, secure communications, reconnaissance, surveillance |
| IoT Networks | Low-power wide-area networks, directional coverage for sensors |
| Vehicle Communications | V2X communications, autonomous vehicles, collision avoidance |
| Indoor Positioning | Location-based services, asset tracking, emergency services |
Key Smart Antenna Technologies:
- Switched Beam: Predetermined fixed beam patterns
- Adaptive Array: Dynamic beam adjustment based on signal environment
- MIMO (Multiple Input Multiple Output): Multiple antennas for spatial multiplexing
Mnemonic: “SWIM-MIV: Satellite, Wireless, IoT, Military, Mobile, Indoor positioning, Vehicles”
Question 5(c) OR [7 marks]#
Explain Terrestrial mobile communication antennas and also discuss about base station and mobile station antennas
Answer:
Diagram: Terrestrial Mobile Communication System
graph TD
A[Base Station] --- B[Mobile Station]
A --- C[Mobile Station]
A --- D[Mobile Station]
E[Base Station Antennas] --- F[High Gain<br>Sectorized]
E --- G[Omnidirectional]
E --- H[Smart Antennas]
I[Mobile Antennas] --- J[Whip/Monopole]
I --- K[Helical]
I --- L[PIFA/Patch]
style A fill:#f9f,stroke:#333
style I fill:#bbf,stroke:#333
Base Station Antennas:
| Antenna Type | Characteristics | Applications |
|---|---|---|
| Omnidirectional | - 360° horizontal coverage - 6-12 dBi gain - Vertical polarization - Collinear arrays | - Rural areas - Low traffic density - Small cells |
| Sectorized | - 65-120° sector coverage - 12-20 dBi gain - Vertical/slant polarization - Panel design | - Urban/suburban areas - Frequency reuse - High capacity networks |
| Diversity Antennas | - Multiple elements - Space/polarization diversity - Reduced fading | - Multipath environments - High reliability links |
| Smart Antennas | - Adaptive beamforming - Multiple elements - 15-25 dBi gain | - High capacity areas - Interference reduction - 4G/5G systems |
Mobile Station Antennas:
| Antenna Type | Characteristics | Applications |
|---|---|---|
| Whip/Monopole | - External antenna - λ/4 length - Omnidirectional - 2-3 dBi gain | - Vehicle-mounted phones - Older handsets - Rural area devices |
| Helical | - Compact size - Good bandwidth - Flexible design - 0-2 dBi gain | - Portable radios - Early mobile phones |
| PIFA (Planar Inverted-F) | - Internal antenna - Compact size - Multiband operation - 0-2 dBi gain | - Modern smartphones - Tablets - IoT devices |
| Patch/Microstrip | - Low profile - Directional pattern - Dual polarization - 5-8 dBi gain | - Data cards - Fixed wireless terminals - High-speed data devices |
Key Considerations for Mobile Communication Antennas:
Base Station Requirements:
- High gain for coverage
- Focused beams for capacity
- Downtilt to control interference
- Diversity for multipath mitigation
- Weather resistance
Mobile Station Requirements:
- Small size and low profile
- Multiband operation
- Omnidirectional pattern
- SAR (Specific Absorption Rate) compliance
- Integration with device design
Mnemonic: “BOMBS-WHIP: Base Omni/Multi-Beam/Smart, Whip/Helical/Inverted-F/Patch”