RF Prediction Accuracy with 2 MHz DFD Error

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.

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: 150 MHz

Sinusoidal Period: 1.667 ms

PRI: 400 us (approximately 4 PRI per RF cycle)

The DFD resolution is 1 MHz and the DFD error is 2 MHz. 

click here to begin video clip

Although the oscilloscope trace shows features such as lock time and error voltage it is difficult to see how accurate the predictions are overall.  The PCT as the ability to measure the PRED effectiveness when performing RF prediction.  The vertical bar on the right side of the figure below shows that the PRED is issuing a predicted RF value that is within 5 MHz of the actual RF value virtually 90% of the time.

In contrast, when the DFD error was only 1 MHz, the PRED-RF achieved about 95% effectiveness.

It is also interesting to look 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. 

This can be contrasted to the results provided for a 1 MHz DFD error which shows considerably less output error.  It can also be compared to the results for the other emitter which again shows a different error profile.

The prediction depends heavily on the quality of the data being fed into the predictor.

click here to begin video clip