Variables Relationships

Question 1

Relationship PRI vs PRF

Answer 1

Inverse

PRF = 1 / PRI

Question 2

Max Unambiguous Range formula basic relationship

simple system

Answer 2

Bigger the PRI, bigger the MUR

MUR = cPRI / 2

Question 3

Range Resolution formula basic relationship

simple system

Answer 3

Bigger the PW, bigger the range resolution

Rr = (c . tau) / 2
tau = PW

Question 4

Blind Range formula basic relationship

simple system

Answer 4

Bigger the PW, bigger the blind range

Br = c . tau
tau = PW
(Basic speed/ distance/ time equation)

Question 5

Beamwidth formula relationships

simple system

Answer 5

Greater the antenna width, the smaller the beamwidth

Greater the wavelength, the greater the beamwidth

(ThetaB = lambda / antenna width)

Question 6

Gain formula relationships

simple system

Answer 6

Greater the Ae, greater the Gain

Greater the lambda, the inverse square reduction on Gain

G = Ae (4pi) / lambda^2

Question 7

Maximum number of pulses relationships

Answer 7

Greater the Duty cycle, OR beamwidth, greater the max number of pulses

Greater the PRI, smaller the max number of pulses

Question 8

Average Power equation

Answer 8

Ave Pwr =

Peak Pwr x PW x PRF

Question 9

What is a method to use a bigger PW without sacrificing Range Resolution?

Where in the radar system does the function actually happen?

Answer 9

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

Question 10

What is Pulse compression used for?

Answer 10

Discrimination of > 1 targets within 1 pulse

Question 11

Range resolution relationships FOR CHIRP

Answer 11

Greater the bandwidth, the smaller the Range Resolution

Rr (with chirp)
= c / 2B

Question 12

How does Range relate to:
- Transmit Power
- Recieved Power
in the Radar equation?

Answer 12

Transmit Power is proportional to Range^4

Received Power is inversely proportional to Range^4

Question 13

How can you increase Probability of detection (Pd) of a pulse radar wrt SNR?

Answer 13

Increasing the power will “shift” the Signal curve reducing the overlap between Signal and Noise

Question 14

What does a CW radar detect?

What doesn’t it detect compared to a pulse radar?

Answer 14

CW radar detects Motion/ velocity

Doesn’t detect range

Question 15

Doppler frequency; how does lambda relate to it?

Answer 15

Lambda is inversely proportional to doppler frequency

• so higher the freq, better detection of moving tgts

fD = - (2V(relative) / lambda)

Question 16

Duty Cycle formulas regarding:

• PRI vs tau
• Ave vs Max power

Answer 16

Duty Cycle
= tau / PRI
= P(ave) / P(max)

Question 17

What can be used to aid detection of targets beyond MUR?

Answer 17

Jitter

Changes PRI between pulses; processed post-receiving

Question 18

What is the advantage of a CW radar over a pulse radar wrt detection through the antenna?

Answer 18

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

Question 19

How does the beamwidth of a steered beam vary with angle off broadside (aka flat)?

Answer 19

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’))

Question 20

How does the gain vary with angle off broadside in a phased array?

Answer 20

As angle off (Theta ‘s’) increases, gain decreases, as the apparent antenna length also reduces with an increasing Theta ‘s’