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RF Prediction Accuracy
with 2 MHz DFD Error - another emitter
Sinusoidal RF patterns (e.g. spin-tuned magnetron) give the radar an
inherent ECCM capability since they appear to be random from pulse
to pulse. RF prediction is needed in order to control a
DRFM or VCO properly so that up-range false targets can be generated
effectively.
In order
to see how accurately the PRED-RF can predict the sinusoidal RF
pattern of an emitter, a test is conducted where DFD words are
generated by the PCT and fed into the PRED-RF. 40 acquisition
loops are performed starting at different places (i.e. phases) in
the pattern in order to look at overall performance. Each
acquisition loop consists of 1000 PRI and the PCT counts the number
of times that PRED-RF is able to correctly predict the RF of the
next pulse. To be correct, the predicted RF needs to be within
5 times the resolution of the DFD and be available at least one half
PRI before the arrival of the pulse. A histogram of the error
can be found in the "Results" section of this CD.
RF
Prediction accuracy is emitter dependant.
In order to demonstrate this, the performance against a second
emitter is tested.
This video clip shows 2 traces of an oscilloscope display. The
Blue
trace shows the error recorded on the VCO control signal - 1
division = 10 MHz of error. The
Yellow
trace shows the predictors "Lock" output signal which goes high when
the algorithm locks onto the RF pattern.
In this
case the signal is a sinusoidal RF with:
Mean RF:
9100 MHz
Deviation: 200 MHz
Sinusoidal Period: 2.333 ms
PRI: 50
us (approximately 47 PRI per RF cycle)
The DFD
resolution is 1 MHz and the DFD error is 2 MHz.
click here to begin video clip
As shown
below, the PRED-RF is about 93% effective in predicting this RF
agility pattern.
This
video can be contrasted with the videos of the first emitter -
for this emitter, the errors are somewhat smaller and the Prediction
Effectiveness is higher (93% vs 90%) even though the input errors
are equal.
This can
be further demonstrated by looking at the instantaneous input error
(caused by the DFD) vs the output error (predicted RF - actual RF).
This video clip shows 2 traces of an oscilloscope display. The
Blue
trace shows the error recorded on the VCO control signal - 1
division = 10 MHz of error. The
Yellow
trace shows the input error to the PRED caused by the DFD.
There is good correlation between these 2 signals - the PRED-RF is
adding little in the way of error.
click here to begin video clip
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