In our previous White Paper regarding Phase 1 of improving the F-16C and F/A-18C radars, we discussed advances in how we calculate detection range based on Pulse Repetition Frequency (PRF), average transmitted power, receiver noise figure, antenna area, and Signal to Noise Ratio (SNR). You can find this White Paper here:
For Phase 2 of radar model update, we will be accounting for the following:
Fluctuation of Target RCS. Real targets have complex shapes, and their linear sizes are often larger than radar wavelength. This means that radar returns from different parts of the airframe may add or cancel each other depending on their relative phase causing the RCS to fluctuate. In our approach, RCS is approximately constant during dwell, but randomly changes from dwell to dwell according to exponential distribution (this approach is known as the Swerling Case I model). This results in non-constant detection range and target detection probability.
Noise Variability. Detection probability will also depend on the noise level, its variability, and the number of Coherent Processing Intervals (CPIs) per dwell. Because the noise level continuously changes, the target may or may not be detected in a particular CPI. For example: There are three CPIs per dwell in HPRF RWS mode, and for successful ranging, the target should be detected in all three CPIs. Obviously, the probability of detection in all three CPIs is lower than the probability of detection in one of three CPIs or in three of eight CPIs (like in MPRF mode). In HPRF Velocity Search mode, Post-Detection Integration (PDI) replaces Frequency Modulation Ranging (FMR). In that mode, signals from three CPIs are summed to make noise fluctuations smaller and thus minimise the probability of false alarms. This allows lower threshold sensitivity and increased detection range without increasing false alarm probability.
Mode-Specific Range and Doppler Resolution. Closely spaced targets may not be resolved individually, and they may be displayed as a single target. Return energy off such targets may fall into a single doppler range bin and result in detection at longer ranges. Velocity resolution depends on CPI duration. So, in HPRF with three CPIs per dwell resolution is better than that in MPRF mode with eight CPIs per dwell (dwell duration is constant, so CPIs are shorter). In RAID mode, up to four CPIs may be merged into one, thus increasing velocity resolution four times. RWS HPRF mode uses linear frequency modulation for ranging, and it has poor range resolution (in order of 2 nm, which improves four times in RAID mode). In MPRF mode, range resolution is defined by range bin size and it is always equal to 150 meters.
Atmospheric Propagation Loss. The atmosphere absorbs radio waves proportional to its density. So, at higher altitudes, detection range is greater than at low altitude.
In summary, the Phase 2 changes provide a more realistic simulation of radar detection probabilities that will have more variable detection ranges, low-quality/spurious detections, more accurate RCS effects, and modelling of radar modes.
In Phase 3 we will focus on false targets, look-down performance, and improved modelling of Single Target Track (STT) mode.