EO-8

Question 1

What does the radar use doppler shift to calculate what?

Answer 1

Target relative velocity

Question 2

If the target is moving towards the radar system..

Answer 2

the doppler shift will be positive (returned frequency is higher than the transmitted RF)

Question 3

If the target is moving away from the radar system…

Answer 3

the doppler shift will be negative (returned frequency is lower than the transmitted RF)

Question 4

What is the relationship of the target’s relative velocity and the actual speed of the target?

Answer 4

They are not the same. (Velocity = speed & direction)

Question 5

What is the relationship of relative velocity and true velocity?

Answer 5

At any angle >0 and <90, the measured relative velocity is less than the true velocity of the target.

Question 6

What technique is employed by pulsed radar systems to measure the velocities of targets?

Answer 6

Pulse doppler processing

Question 7

Pulse Doppler processing

Answer 7

Samples the radar returns in time domain and converts the samples into the frequency domain using the fast Fourier transform (FFT). The radar then takes the output of the FFT and computes the relative velocity.

Question 8

Coherent Processing Interval (CPI)

Answer 8

An interval in which pulses are transmitted

Question 9

In the case of a pulse constant waveform, what is the CPI?

Answer 9

A predetermined time interval

Question 10

In the case of a dwell-and-switch, what is the CPI?

Answer 10

One dwell period

Question 11

Digital Signal Processing Bandwidth (BWDSP)

Answer 11

The inverse of the sample period for a set of data

Question 12

In pulse doppler processing, the BWDSP is equal to what?

Answer 12

The PRF

Question 13

What are the 3 categories of Pulsed Doppler waveforms?

Answer 13

High PRF, Medium PRF, and Low PRF

Question 14

How are PD modes distinguished?

Answer 14

By the ambiguity regions in both range and velocity.

Question 15

Describe the relationship between the maximum unambiguous range (MUR) and the PRF.

Answer 15

As PRF decreases, the MUR increases; As the PRF increases, the MUR decreases

Question 16

What pulse doppler system is better at determining range?

Answer 16

A low PRF (LPRF) system.

Question 17

When does the relative velocity of a target become ambiguous?

Answer 17

If the true doppler shift is greater than the PRF.

Question 18

Low PRF (LPRF) waveform

Answer 18

Targets are detected unambiguously in range but ambiguously in velocity.

Question 19

Medium PRF (MPRF) waveform

Answer 19

Targets are detected ambiguously in both range and velocity.

Question 20

When are MPRFs typically used?

Answer 20

When two aircraft are traveling in the same direction. (tail chase scenario)

Question 21

When the targets are ambiguous in both range and velocity, how can those ambiguities be resolved?

Answer 21

By using a dwell-and-switch modulation.

Question 22

High PRF (HPRF) waveform

Answer 22

Targets are detected unambiguously in velocity but ambiguously in range.

Question 23

When are HPRFs typically used?

Answer 23

• Targets will be incoming at a high relative velocity (head-to-head airborne scenarios)

Question 24

With HPRF waveforms, how can we resolve range ambiguities?

Answer 24

By using frequency modulated ranging (FMR).

Question 25

Frequency Modulated Ranging (FMR)

Answer 25

A method of indirectly measuring range using linear frequency modulation.

Question 26

While using the FMR technique, what is common for a radar system to do?

Answer 26

Use many different FM rates

Question 27

In relation to FMR, what is required to determine range and velocity of a single target?

Answer 27

It takes 2 different sweep rates. (Zero is considered a rate)

Question 28

In relation to FMR, what is required to determine range and velocity of multiple targets?

Answer 28

The radar must sweep at least one more rate than the number of targets the radar is trying to differentiate.