EO-8 Flashcards
What does the radar use doppler shift to calculate what?
Target relative velocity
If the target is moving towards the radar system..
the doppler shift will be positive (returned frequency is higher than the transmitted RF)
If the target is moving away from the radar system…
the doppler shift will be negative (returned frequency is lower than the transmitted RF)
What is the relationship of the target’s relative velocity and the actual speed of the target?
They are not the same. (Velocity = speed & direction)
What is the relationship of relative velocity and true velocity?
At any angle >0 and <90, the measured relative velocity is less than the true velocity of the target.
What technique is employed by pulsed radar systems to measure the velocities of targets?
Pulse doppler processing
Pulse Doppler processing
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.
Coherent Processing Interval (CPI)
An interval in which pulses are transmitted
In the case of a pulse constant waveform, what is the CPI?
A predetermined time interval
In the case of a dwell-and-switch, what is the CPI?
One dwell period
Digital Signal Processing Bandwidth (BWDSP)
The inverse of the sample period for a set of data
In pulse doppler processing, the BWDSP is equal to what?
The PRF
What are the 3 categories of Pulsed Doppler waveforms?
High PRF, Medium PRF, and Low PRF
How are PD modes distinguished?
By the ambiguity regions in both range and velocity.
Describe the relationship between the maximum unambiguous range (MUR) and the PRF.
As PRF decreases, the MUR increases; As the PRF increases, the MUR decreases
What pulse doppler system is better at determining range?
A low PRF (LPRF) system.
When does the relative velocity of a target become ambiguous?
If the true doppler shift is greater than the PRF.
Low PRF (LPRF) waveform
Targets are detected unambiguously in range but ambiguously in velocity.
Medium PRF (MPRF) waveform
Targets are detected ambiguously in both range and velocity.
When are MPRFs typically used?
When two aircraft are traveling in the same direction. (tail chase scenario)
When the targets are ambiguous in both range and velocity, how can those ambiguities be resolved?
By using a dwell-and-switch modulation.
High PRF (HPRF) waveform
Targets are detected unambiguously in velocity but ambiguously in range.
When are HPRFs typically used?
- Targets will be incoming at a high relative velocity (head-to-head airborne scenarios)
With HPRF waveforms, how can we resolve range ambiguities?
By using frequency modulated ranging (FMR).
Frequency Modulated Ranging (FMR)
A method of indirectly measuring range using linear frequency modulation.
While using the FMR technique, what is common for a radar system to do?
Use many different FM rates
In relation to FMR, what is required to determine range and velocity of a single target?
It takes 2 different sweep rates. (Zero is considered a rate)
In relation to FMR, what is required to determine range and velocity of multiple targets?
The radar must sweep at least one more rate than the number of targets the radar is trying to differentiate.
