Radar theory Flashcards
What principle does radar work on
Echo
What does the quality of a radar return depend on
Size of object
Shape of object
Material
Can you receive when you’re transmitting
No
What is a phased array
Sweeps electronically
Requires 3/4 for 360° sweep
What is a parabolic dish
Required 1 for 360° sweep
Better coverage than a phased array
What beam width is better for accuracy
Smaller beam width
What size dish is better for beam width accuracy
Bigger dish = smaller beam width = better accuracy
What happens to unambiguous theoretical range as pulses per second increase
Range decreases
What happens if pulse repetition frequency (PRR) / pulse recurrence rate (PRR) is too high
May receive target echos from wrong pulse
What happens to unambiguous range with a high PRF
Less range
Dish rotates quickly
What is the formula for max unambiguous range
81000nm / PRF
What is the max range or radar
Line of sight
1.23 ( * squareroot* height of transmitter + squareroot height of receiver)
What is the min theoretical range of radar
Pulse width 1 microsecond = 150m
What happens below min theoretical radar range
Dead area
What effect does atmospheric conditions have on radar
Radiowaves degrades by:
- water vapour / temperature changes / pressure changes
Energy absorbed by water vapour and converted to heat
Further radar signal travels = the more atmospheric attenuation
More pronounced at high frequencies
What is ducting / super refraction
Radar beam bends towards the earths surface
Usually caused by strong low level inversions
More common in mornings
Increases radar range
Does now affect unambiguous range
What is sub refracting
Opposite of super refraction
Radar signals to be refracted away from earths surface more than normal
Formed by warm moist air moving over a cooler drier surface
Reduction in radar max range
What types of radar are there (radar stations on the ground)
Area / terminal area radars :
Usually long range - low PRF - low rpm
Surveillance radars :
Shorter range - higher PRF - faster rotating
Ground radar :
Very high PRF
What is a moving target indicator system (MTI)
Removes ground clutter from radar
Used Doppler effect
Anything with no shift is removed
Jitters the PRF
What is a air traffic service
En route atc
Long range radars
What is a terminal surveillance area radar
Providing positioning aircraft for handoff to individual airfields
What is airfield approach radar
Short range
For position to final approach
What is guidance service radar
For controlled airspace
