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Old 06-21-2019, 08:57 AM   #1
mattag08
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Default Radar Warning Receivers

Background: RWRs track a wide spectrum of radar-band frequencies and use various signal processing techniques to determine what is and is not a military search or fire control radar. The signals are processed and analyzed against known threats. The RWR will then return a warning along with the type and threat level based on this processing.

From the point of view of a player with no classified knowledge of EW, but a background in physics and computing, there are areas where DCS's RWR modeling seems to fall short:

1. Radar wash and radar limits - aircraft often receive an FCR lock ("spike") indication, FCR guidance (missile launch) indication, or active radar missile homing indication when the source radar is of no threat to the aircraft in question or is well outside reasonable parameters. The beam width of a typical FCR is generally less than 1°. As a rule of thumb, this means the width of the beam is less than 1 NM for each 60 NM the radar energy travels. At ranges of less than 10 NM, the beam width is on the order of 0.1 NM.

Currently in DCS, lock and guidance indications, which occur in a situation where the radar antenna is trained on a specific target and no longer sweeping, appear on the RWR of other nearby aircraft with an extremely high frequency, even when the aircraft is significantly offset outside of the normal beam width. Additionally, for threats such as active radar homing missiles, the active radar missile warning indication appears for a significant period of time after the missile is no longer a threat. In fact, the aircraft can be behind the missile's seeker head and still receive the threat indication.

2. Radar strength and rejection - It stands to reason that RWRs have logic filters that would eliminate physical impossibilities from being displayed. Radio emissions follow the inverse square law. RWRs can detect the strength of the emission and determine the range, and thus threat level, of the source radar based on a threat catalog. Likewise, this catalog would know the maximum possible detection and launch ranges of the platforms involved. This mean an RWR should, for instance, reject a launch/guidance warning from a source radar that is beyond a reasonable distance to engage the aircraft. For example, an F/A-18C that launches an AIM-7 would generate a launch warning for any aircraft that received sufficient energy to indicate that the F/A-18C was at a reasonable range to guide a semi-active missile. Allowing for error and unknown factors (such as missile improvements), this range would likely be 40 NM at most (since a reasonable range for the missile is at best, 20 NM).

Additionally, the known capability of the FCR radar itself would be taken into account. If the radar is only capable of detecting fighter-sized targets at approximately 40 NM. It would be reasonable for the RWR to reject any radar guidance warnings of a strength that indicates that the particular radar is outside of 40 NM.

Currently in DCS it is possible to receive missile guidance and lock warnings from platforms well outside of their detection range let alone that particular platform's best missile Rmax. This physical impossibility should be filtered out by the RWR.

3. Warning decay times - RWRs must balance probability of warning (POW) against false alarm rates (FAR). This means that there is some signal processing time that must occur for the RWR to determine whether or not the received radar energy is in fact a threat radar and then to classify that threat. Higher confidence reduces false alarms, but increases the processing time. However, in aerial engagements, this increased processing time also comes at another price, the inability of an aircraft to know when he is "naked". In other words, how quickly the pilot is made aware that the enemy has stopped locking, guiding, or searching for his aircraft. This information is vital in beyond visual range missile engagements.

Currently in DCS, warning decay times are excessive. Multiple seconds elapse between a threat disappearing and the warning stopping. At best, 1-2 seconds is the longest period a threat should remain after the source signal is lost.

All of these issues means that RWR usage in DCS is difficult at best and worthless at other times. A DCS pilot simply cannot rely on the RWR to produce accurate, useful warnings in a busy battlespace. Only in small-scale, set-piece air battles can a pilot expect to be able to use the RWR to a reasonable degree.

The above is based on my personal testing and observations in the sim and my own reading and knowledge on the various physical principles involved. I would be interested to know what other people think or if there is other evidence that demonstrates that DCS's RWR modelling is actually accurate.
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