Radar Fundamentals - Faculty
[Pages:51]Radar Fundamentals
Prof. David Jenn Department of Electrical & Computer Engineering
833 Dyer Road, Room 437 Monterey, CA 93943 (831) 656-2254
jenn@nps.navy.mil, jenn@nps.edu
Overview
? Introduction ? Radar functions ? Antennas basics ? Radar range equation ? System parameters ? Electromagnetic waves ? Scattering mechanisms ? Radar cross section and stealth ? Sample radar systems
2
Radio Detection and Ranging
? Bistatic: the transmit and receive antennas are at different locations as
viewed from the target (e.g., ground transmitter and airborne receiver).
? Monostatic: the transmitter and receiver are colocated as viewed from
the target (i.e., the same antenna is used to transmit and receive).
? Quasi-monostatic: the transmit
and receive antennas are slightly
separated but still appear to
be at the same location as RECEIVER
viewed from the target
(RX)
(e.g., separate transmit
and receive antennas on
the same aircraft).
TRANSMITTER (TX)
SCATTERED WAVE FRONTS
Rr
Rt
TARGET
INCIDENT WAVE FRONTS
3
Radar Functions
? Normal radar functions: 1. range (from pulse delay) 2. velocity (from Doppler frequency shift) 3. angular direction (from antenna pointing)
? Signature analysis and inverse scattering: 4. target size (from magnitude of return) 5. target shape and components (return as a function of direction) 6. moving parts (modulation of the return) 7. material composition
? The complexity (cost & size) of the radar increases with the extent of the functions that the radar performs.
4
Electromagnetic Spectrum
Wavelength (, in a vacuum and approximately in air)
Microns 10-3 10-2 10-1 1
Meters 10-5 10-4 10-3 10-2 10-1 1
101 102 103 104 105
EHF SHF UHF VHF HF MF LF Radio
Microwave Millimeter
Ultraviolet
Infrared Visible
Typical radar frequencies
Optical
300 GHz
300 MHz
109 108 107 106 105 104 103 102 10 1 100 10 1
100 10
1
Giga
Mega
Kilo
Frequency (f, cps, Hz)
5
Radar Bands and Usage
8
(Similar to Table 1.1 and Section 1.5 in Skolnik)
6
Time Delay Ranging
? Target range is the fundamental quantity measured by most radars.
It is obtained by recording the round trip travel time of a pulse, TR , and computing range from:
Bistatic: Rt + Rr = cTR
Monostatic: R = cTR 2
(Rt = Rr = R)
where c = 3x108 m/s is the velocity of light in free space.
TRANSMITTED PULSE
RECEIVED PULSE
AMPLITUDE
TR
TIME 7
Classification by Function
Radars
Civilian
Weather Avoidance
Military
Navagation & Tracking
Search & Surveillance
High Resolution Imaging & Mapping
Space Flight Proximity Fuzes
Sounding
Countermeasures
8
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