Variables Relationships Flashcards
Relationship PRI vs PRF
Inverse
PRF = 1 / PRI
Max Unambiguous Range formula basic relationship
simple system
Bigger the PRI, bigger the MUR
MUR = cPRI / 2
Range Resolution formula basic relationship
simple system
Bigger the PW, bigger the range resolution
Rr = (c . tau) / 2
tau = PW
Blind Range formula basic relationship
simple system
Bigger the PW, bigger the blind range
Br = c . tau
tau = PW
(Basic speed/ distance/ time equation)
Beamwidth formula relationships
simple system
Greater the antenna width, the smaller the beamwidth
Greater the wavelength, the greater the beamwidth
(ThetaB = lambda / antenna width)
Gain formula relationships
simple system
Greater the Ae, greater the Gain
Greater the lambda, the inverse square reduction on Gain
G = Ae (4pi) / lambda^2
Maximum number of pulses relationships
Greater the Duty cycle, OR beamwidth, greater the max number of pulses
Greater the PRI, smaller the max number of pulses
Average Power equation
Ave Pwr =
Peak Pwr x PW x PRF
What is a method to use a bigger PW without sacrificing Range Resolution?
Where in the radar system does the function actually happen?
Pulse Compression
- Allows a big pulse to be transmitted
- pulse is coded (e.g. by stepping frequency)
The actual compression of the pulse happens during post-receiving processing
Allows discrimination of > 1 targets within 1 Pulse
What is Pulse compression used for?
Discrimination of > 1 targets within 1 pulse
Range resolution relationships FOR CHIRP
Greater the bandwidth, the smaller the Range Resolution
Rr (with chirp)
= c / 2B
How does Range relate to:
- Transmit Power
- Recieved Power
in the Radar equation?
Transmit Power is proportional to Range^4
Received Power is inversely proportional to Range^4
How can you increase Probability of detection (Pd) of a pulse radar wrt SNR?
Increasing the power will “shift” the Signal curve reducing the overlap between Signal and Noise
What does a CW radar detect?
What doesn’t it detect compared to a pulse radar?
CW radar detects Motion/ velocity
Doesn’t detect range
Doppler frequency; how does lambda relate to it?
Lambda is inversely proportional to doppler frequency
- so higher the freq, better detection of moving tgts
fD = - (2V(relative) / lambda)
Duty Cycle formulas regarding:
- PRI vs tau
- Ave vs Max power
Duty Cycle
= tau / PRI
= P(ave) / P(max)
What can be used to aid detection of targets beyond MUR?
Jitter
Changes PRI between pulses; processed post-receiving
What is the advantage of a CW radar over a pulse radar wrt detection through the antenna?
A pulse radar will not be able to receive whilst transmitting so will have a blind range; a CW radar will always be on receive simultaneously to transmitting
How does the beamwidth of a steered beam vary with angle off broadside (aka flat)?
As angle-off (Theta ‘s’) increases, beamwidth also increases, as apparent antenna length (cos (theta ‘s’)) will reduce with an increase in Theta ‘s’.
Beamwidth = lambda / (L cos(Theta ‘s’))
How does the gain vary with angle off broadside in a phased array?
As angle off (Theta ‘s’) increases, gain decreases, as the apparent antenna length also reduces with an increasing Theta ‘s’
