Radar Flashcards
Discuss radar wave propagation: polarization
Orientation of the electrical field creaded by radar waves. Can be horizontal, vertical, sland and circular
Discuss radar wave propagation: power
Strength of the radar signal hitting the target
Discuss radar wave propagation: reflection
The process of reradiation an incident radio wave
Discuss radar wave propagation: refraction
The bend of Em energy
Discuss radar wave propagation: diffraction
Phenomenon observed when a radio wave spreads around objects whose size is comparable to its wavelength and bends aroudn the edges of larger objects
Discuss radar wave propagation: ducting of radar waves
Subrefraction decreases radar LOS by bending the radar beam upward, decreasing its range. Suberrefraction increases the radar LOS detection by bending the beam downward, increasing the radar horizon.
Discuss the charateristics of parabolic antennas
Low antenna gain, low efficiency and large sidelobes (disadvantages) Easiest and cheapest to manufacture (advantage)
Discuss Electronically Scanned Array ESA characteristics
Individual radiating elements make up the antenna array. Mounted in a fixed position. Steering is by individually controlling the phase of the radio
Differences in passive and active ESA
Passive: Operates in conjunction with the same type of central transmitter and receiver as an MSA. Beam is steered by a phase shifter placed behind radiating elements. Active: Instead of a phase shifter, a small T/R module is placed behind radiating elements
Discuss limitations of ESA antennas
Apparent size of the antenna decreases when viewed from angels off boresight. Electronically complex
Discuss pulsed-radar operations
Pulse radar transmits radio waves in short pulses and listens for echoes in periods between pulses.
Discuss pulsed-radar operations: PW
The time the radar is transmitting each pulse
Discuss pulsed-radar operations: PL
Distance between the leading and trailing edges of a pulse
Discuss pulsed-radar operations: range resolution
Radars ability to resolve multiple targets in range
Discuss pulsed-radar operations: range cell
Smallest amount of 3-D airspace in which a radar cannot distinguish between multiple targets
Discuss pulsed-radar operations: PRF
Rate at which pulses are transmitted
Discuss pulsed-radar operations: pulse ranging
Radar transmits RF, RF reflects off a target, RF echos are received. Time between transmit and receive is converted to range
Discuss pulsed-radar operations: range rate
computed based on the basis of change in measured range with time.
Discuss CW/Doppler radar characteristics
Shift in frequency of an Em wave radiated, reflected or received by an object in motion.
How does a CW/Doppler radar measure target velocity
Very accurate method to measure target velocity 1 kt = 35Hz shift 1000ft/s = 20kHz shift March 1 = 20kHz 1 kHz = 30 knots
CW/Doppler radar canceling ground clutter
Target return signal compete with signals returned from the ground. Can be filtered out using Doppler processing
Effects of mainbeam and sidelobe clutter on target detection using CW/Doppler
Mainbeam clutter Bad when searching for aircraft, good for ground maping. Sidelobes are lower in amlitude due to power output. Sidelobes have less doppler shift due to angular difference
List the advantages and disadvantages of CW/Doppler radar
Advantages: Can filter out ground clutter, High AOP increases detection range, very accuratge velocity measurement, good agaisnt high aspect angle targets, simple Disadvantages: Two antennas required: more weight and space, No range info, Susceptible to doppler notch, degraded capes agaisnt beam and stern targets
List the advantages and disadvantages of PD radars
Advantages: Only one antenna required, Filters out ground clutter, High output power, Good all aspect capes Disadvantages: Complicated electronics, susceptible to the doppler notch, Range reasurements difficult with an HPRF PD radar
