Introduction to RADAR

Introduction to RADAR

• RADAR stands for RAdio Detection And Ranging.
• RADAR uses radio waves to detect and measure objects, functioning as an electronic eye.
• RADAR works by emitting electromagnetic waves and analyzing the reflected waves or echoes.
• RADAR is effective day or night, in various weather conditions, and over land, air, or sea.
• RADAR can detect stationary or moving objects, regardless of weather conditions, except when objects are hidden behind good conductors

Information Provided by RADAR

• Position.
• Distance.
• Size.
• Motion status (stationary or moving).
• Velocity.
• Identification of friendly or enemy aircraft.
• Images in good and bad weather.
• Target recognition.
• Trajectory (approaching or receding).
• Direction of movement.
• Classification of materials.

RADAR Applications

• Determining speeds of objects like automobiles and balls.
• Controlling guided missiles and other weapon systems.
• Delivering early warnings.
• Guiding aircraft, ships, submarines, and spacecraft for defense.
• Weather forecasting, remote sensing, and ground mapping.
• Airport control and surveillance.
• Measuring distances for land surveying with precision.
• Detecting underwater objects.
• Navigation for various vehicles.
• Avoiding collisions by detecting ships, land features, and sea conditions.
• Mapping land and sea from air and space.
• Studying celestial objects
• Measuring altitude for navigation.
• Searching for submarines and landmasses.
• Assisting in bombing operations.
• Aiming at enemy targets.

Types of RADAR

• Speed trap.
• Missile tracking.
• Early warning.
• Airport control.
• Navigation.
• Astronomy.
• Ground mapping.
• Weather forecast.
• Gunfire control.
• Remote sensing.
• Tracking.
• Search.
• Identification Friend or Foe (IFF).
• Synthetic aperture.
• Missile control.
• Moving Target Indication (MTI).
• Navy.
• Doppler.
• Mesosphere, Stratosphere, Troposphere (MST).
• Over-The-Horizon (OTH).
• Monopulse.
• Phased array.
• Instrumentation.
• Gun direction.
• Airborne weather.

Historical milestones in RADAR development

• 1886-1888: Heinrich Hertz demonstrated radio wave generation and reception.
• 1903-1904: Christian Hulsmayer invented a basic collision avoidance CW radar.
• 1922: MG Marconi created angle-only CW radar for ship collision avoidance.
• AH Taylor and Young developed CW bistatic radar for harbor.
• 1924-1926: pulse radars were reported.
• 1930: LA Hyland reported radar for aircraft detection.
• 1934: RN Page reported short pulse echo from an aircraft.
• 1937: Sir Robert Watson Watt designed and installed chain-home radar in the UK.
• 1941: USA developed early warning radars.
• Korean War: FM radars were utilized
• World War II: Radar were used for control, communication, and remote sensing.
• Germany developed 'Lichtenstein' radar for air-to-air use.
• 1941-1945: VHF radar with dipole array antenna was used on aircraft.
• USA and UK used magnetron-based microwave airborne radars.

Radar Parameters and Components

• RADAR: A device for detection, ranging, tracking, and searching.
• Echo: A reflected electromagnetic wave received by a radar receiver.
• Duplexer: A microwave switch that alternately connects the transmitter and receiver to the antenna.
• Antenna: A transducer between the transmitter and space, acting as a source and a sensor of electromagnetic waves.
• Transmitter: Generates high-power RF energy using components like magnetrons or klystrons.
• Receiver: Amplifies weak return pulses and separates noise and clutter.
• Synchronizer: Coordinates timing for range determination and regulates pulse reception.
• Display: Presents received information visually, showing echoes.
• Bearing/Azimuth Angle: Angle from true north in the horizontal plane, indicating antenna beam direction.
• Elevation Angle: the angle between the horizontal plane and the line of sight

Radar Range and Wave Properties

• Range of Radar: Distance to the object.
• R = (v0 * ∆t) / 2.
  • v0 is the velocity of the EM wave which is approximately 3 × 10^8 m/s.
  • ∆t: is the echo reception time.
• Radar Pulse: Modulated radiated frequency carrier wave that influences antenna size and beam width.
• Resolution: Ability to separate and distinguish targets of features.
• Four dimensions of target resolution: range, horizontal cross-range, vertical cross-range and Doppler shift.
• Range Resolution (RS): Distinguishes targets at different ranges with the same bearing, measured in distance.
• RS = (v0 × PW(τ)) / 2, where PW is the pulse width.
• Bearing Resolution: Distinguishes objects in different bearings at the same range in degrees.
• Cross-Range Resolution: Distinguishes targets at the same range with linear dimensions like azimuth and elevation.
• Cross-range resolution (∆x): ∆x = (Rλ) / leff,
  • R is the target range.
  • λ is the wavelength.
  • leff is the effective antenna length in the beamwidth direction.
• Doppler Resolution: Ability to distinguish targets at the same range with different radial velocities.
  • ∆fd = 1 / Td
  • Td is the observation time.
• Radar Signal: Carries information as voltage or current, including echoes and noise.
• Radar Beam: Represents field strength or power variation as a function of angle.
• Radar Beamwidth: Width of the main beam between half-power points, measured in degrees.
• Search Radars: Detect targets and determine range, angular velocity and sometimes velocity.

Pulse Characteristics

• Pulse Width: Duration of radar pulse influencing total pulse energy also representing transmitter ON time.
• Pulse Interval Time/Rest Time (PRT): The interval between pulses.
  • PRT = Pulse Repetition Time (PRT) - Pulse Width (PW).
• Pulse Repetition Frequency (PRF): Pulses transmitted per second in hertz
  • PRF = 1 / PRT.
• Pulse Repetition Time (PRT): Time between the start of one pulse and the next
  • PRT = PW + PRT.
• Duty Cycle (Dc): Ratio of average to peak power with no units, and it can be expressed as:
  • Duty cycle = PW × PRF = PW / PRT = Pav / Ppeak
• Average Power: Transmitted power over the pulse repetition period.
  • Pavg = Ppk. pw. prf

Two- and Three-Dimensional Radars

• Two-Dimensional Radars determine range and bearing of targets.
• Three-Dimensional Radars determine altitude, range, and bearing.

Specialized Radar Systems

• Target Resolution Radar: Radar's ability to distinguish targets close in range or bearing.
• Navigational Radars: Similar to search radars, they use short waves reflected from the earth and obstacles.
• Weather Radars: Radiate EM waves with circular/horizontal/vertical polarization.
• Radar Altimeter: For determining aircraft altitude.
• Air Traffic Control Radars: Primary and secondary radars for air traffic control.
• Primary Radars: Receive all echoes.
• Secondary Radars: Transmit pulses and receive digital data from aircraft transponders like altitude.
• Pulse Radar: Emits high-power pulses and analyzes echoes.
• CW Radar: Transmits and receives continuous high-frequency signals.
• Unmodulated CW Radar: Constant amplitude and frequency for measuring speed.
• Modulated CW Radar: Transmits signal with constant amplitude and modulated frequency.
• MTI Radar: Uses Doppler shift to differentiate moving targets.

More Radar Definitions

• Local Oscillator: Generates a frequency signal to convert the received signal into a fixed intermediate frequency.
• Mixer: Combines received signal and local oscillator frequency to produce a fixed intermediate frequency.
• TWT (Traveling Wave Tube): An oscillator using continuous interaction between electron beams.
• Doppler Effect: Shift in frequency due to motion.
• Radar Cross-Section: Measures target's reflected energy and is defined as σ = 4π x (Reflected power/Unit solid angle) / (Incident power/unit area)
• Radome: Antenna cover that protects from the environment and provide efficient shape.
• Blind Speed: the Radial velocity at which targets appear stationary. - vb = PRF x (nλ / 2)
• Radar Beacon: A transponder with a receiver and transmitter.
• Astronomy Radar: Probes celestial objects.
• OTH (Over-The-Horizon) Radar: Operates between 2-30 MHz to see beyond the radio horizon.
• PPI (Plan Position Indicator): A circular display showing target location.
• A-Scope: Represents range vs. target echo amplitude.
• B-Scope: Represents azimuth angle vs. target range.

Types of Radars Continued

• Tracking Radar: Tracks targets and provides range and angle tracking.
• Monostatic Radar: Transmitter and receiver are at the same location with a common antenna.
• Bistatic Radar: Transmitter and receiver are at different locations.
• Laser Radar: Uses a laser beam and operates between 30-300 THz.
• PAR (Precision Approach Radar): Guides aircraft landings using a sharp beam antenna.
• METR (METeorological Radar): Provides weather information using X-band frequencies.
• Remote Sensing Radar: Data about remote places using shaped beam antenna.
• Phased Array Radar: Scans by changing the phase distribution of the array.
• Matched Filter: Optimizes the signal-to-noise ratio.
• Correlation: Matches two waveforms.

Additional Terms

• Ambiguous Range: Range affected by inadequate round trip time.
• Ambiguous Velocity: Velocity affected by by folding over velocities.
• Angle Resolution: Ability to distinguish targets at an angle.
• Angle Tracking: Tracking a target at an angle.
• Aperture: An opening where aperture size determines the electromagnetic energy intercepted.
• Beam Steering: Rotating antenna pattern electronically,
• Beamwidth: the Angular dimension of antenna pattern.
• Boresight: the forward direction.
• Chaff: Material with high radar cross-section used for radar countermeasures.
• Clutter: unwanted signals from echo.
• Coherence: Fixed phase relationship throughout operation.
• Cross-range: Range between targets axis of the antenna.
• Difference Beam: Obtained when field is subtracted.
• False Alarm Rate: Frequency of noise falsely accepted as a signal.
• LIDAR: Light Detection and Ranging.
• Conical Scan: Tracking technique for accurate angular information.
• FFT: Algorithm for finding the frequency content of a digitized time function.
• Pulse Compression: Inserting more bandwidth.
• Radial Velocity of the Target: Target velocity component along the radar line of sight.
• Range Tracking Radar: Tracks targets in range.
• Scanning: Movement of radar beam.
• Scattering: Reflection of electromagnetic energy.
• Sidelobe: Residue of antenna.
• Sidelobe Jamming: Disrupting of signals into sidelobes.
• SNR: Power to noise signal power.
• Solid Angle: An area in angle using "steradian."
• Squint Angle: Angle of synthetic aperture radar.
• Transponder: Radiates energy.
• Unambiguous Range of Radars: Range associated with the time between pulses.
• Blind Range: Range and PRT.

RADAR Classification

• Frequency
• Waveform
• PRF
• Application

Frequency-Based Radar Classification

• HF band radars
• VHF and UHF radars
• L-Band radars
• S- Rayed radars
• C-Band radars
• X-Band radars
• Ku, K, Ka band radars
• Infrared and visible light band radars.

Bands

• HF Band Radars: Operate around 30 MHz and use ionosphere reflection, examples include BOTHER radars, Woodpecker radars.
• VHF Band Radars: Use line-of-sight propagation for long-range detection, examples include early warning and detection of high-altitude targets.
• L-Band Radars: Have small radar wave, examples include long-range search, air traffic control and based.
• S-Band Radars: Are ground shipborne medium range search radars, examples include air traffic control
• C-Band Radars: Used for air ground bone radars.
• X-Band Radars: Reduce antenna size and they include weather multicore radars.
• Ku, K, Ka-Band Radars: High weather bands and they includes, airport surfaces, terrain radars.
• Infrared and Visible Light Band Radars: finders, optical.

Waveform-Based Radar Classification

• Unmodulated CW radars
• Modulated CW radars
• Gated CW pulsed radars
• Complex waveform pulsed radars

PRF-Based Radar Classification

• LPRF (Low Pulse Repetition Frequency).
• HPRF (High Pulse Repetition Frequency).