2. Introduction b Flashcards
What are the target parameters which are measured by radar?
Azimuth angle
Elevation angle
Range
Radial velocity
Polarization
How can we filter out clutter?
Doppler shift (via spectral analysis) and Polarization
These can also give target identification info.
Range Resolution
Two targets that are closely spaced in either range are difficult to distinguish and depends on the pulse width.
Doppler Frequency Resolution
If the Doppler frequencies of two targets are very close, they are difficult to distinguish. Based on Dwell Time.
The higher the pulse burst duration (Dwell Time), the more accurately you can measure a phase shift, resuling in better Doppler Resolution.
4 types of Interference (not atmospheric effects)
Noise
Clutter
Electromagnetic Interference
Jamming
What causes most noise in a radar system?
Thermal Noise: Random thermal motion of charged particles causes all objects above a temperature of absolute zero to radiate EM waves.
This Thermal Noise is both recieved and generated within the receiver.
Probability of Detection and False Alarm
Probability of Detection: Probability a target-plus-noise signal will exceed the threshold. (that anything will exceed threshold)
Probability of False Alarm: Probability that noise alone will exceed threshold.
Describe Diffraction
EM waves will bend around an object or propagate through an aperature.
What causes Atmospheric Attenuation? In general, which frequencies attenuate less? How do we choose what frequencies we operate at according to this?
Different frequencies will have high rates of attenuation due to absorption by H2O and O2 molecules. We therefore tend to design radar frequency ranges in the troughs where there is lower attenuation.
Rain and clouds will also increase attenuation. Lower frequencies tend to attenuate less.
What are 4 types of EM interaction with atmosphere?
Diffraction
Attenuation
Refraction
Reflection
Define Radar Cross Section
The area intercepting that amount of power which, if radiated isotropically, produces the same power in the receiver.
If the object radiated isotropically, what would be its cross sectional area.
What are the mechanisms which determine a target’s RCS?
Interception
Reflection
Directivity
Seach Radar - 2D
Search Radar - 3D
Over the Horizon Search Radar
Detect ICBMs
Tracking / Fire Control Radars
Multifunction Radars
