
Jump to: Board index » Military Aviation » Air Power
hornetfinn wrote:There are several problems with this:
1. Like already noted, VHF/UHF radar have pretty poor resolution. Another problem is that they have poor resolution in 3 dimensions, meaning also height resolution. So this means the missile search volume would be pretty large especially at longer ranges from radar.
2. VHF/UHF radar have quite long time between track updates as they use very large rotating antennas. This is usually in the region of 5 to 20 seconds which makes the real resolution even worse as any change in target speed or heading makes the volume a lot larger.
3. IR missiles have rather narrow Field of View and thus it takes a long time to search a large volume. Of course FoV could be wider, but then range and resolution suffer immediately. Missile going Mach 3+ would have very limited time to search the volume before it could no longer engage the target even if it detected it.
4. VHF/UHF radars are very large and cumbersome systems that are pretty easily detected and geolocated as they are powerful systems with narrow bandwidth (due to low frequency used). Stealth fighters like F-22 and F-35 would very likely know where they are and what they were doing. F-117 was brought down because it had no knowledge about the existence of enemy radars.
Basically it could be done and it could work in some cases, but it's likely not very effective overall especially against fighters with modern ESM/EW systems which could detect the radar. Even if radar could operate freely, the kill probability would be pretty low due to low radar resolution and slow volume search speed for missile seeker. There are a lot of reasons why VHF/UHF radars have not been used for direct target engagements except some anti cruise missile tests. VHF/UHF radars could be used to cue engagement radars though and using sensor fusion techniques could be more of a threat.
armedupdate wrote:1. 2. But isn't resolution not incredibly bad? We aren't talking about 10 km off target? All we need is a missile to fly close enough to ignite the second stage.
3. From what I know IR missiles don't need huge FoVs if it's WVR.
4. True that.
skyward wrote:3. From what I know IR missiles don't need huge FoVs if it's WVR.
That is because the IR missiles is being told where to look by the fighter before launch.
hornetfinn wrote:armedupdate wrote:1. 2. But isn't resolution not incredibly bad? We aren't talking about 10 km off target? All we need is a missile to fly close enough to ignite the second stage.
3. From what I know IR missiles don't need huge FoVs if it's WVR.
4. True that.
It is pretty bad for missile guidance. Generally missiles need very good "weapons grade" target tracking for successful engagement like wrightwing said. Let's think about it for a moment:
VHF radar detects a target say 100 km away from the radar. Each detection has measurement accuracy of say 1000 m in azimuth, about 100 m in range and 3000 m in altitude and detection is updated every 6 seconds (pretty fast for VHF radar). These would be pretty good specs for VHF radar and range is just 100 km. What all this means is that target doing 250 m/s is going to move abut 1500 m between consecutive detections and there is going to be pretty large errors (within the measurement accuracy) in coordinates of each detection on average. If the target is going in straight line, it's fairly easy to predict where it will be next. However, when it's maneuvering even slightly, it's getting a whole lot more difficult with increasing errors in predicting where it will be. Remember that the radar must guide the missile to interception point which is always going to be in the future and missile is going to predicted point.Because of the aforementioned accuracy and slow update interval there is going to be huge uncertainty volume where the missile has to search for a target. For example just the altitude uncertainty is going to be several kilometers in best case.
Target speed calculation is also very tricky due to those errors and slow updates. Say there is 500 m error (half the measurement accuracy) in azimuth in two consecutive detections and target actually moves 1500 m between those two detections. Real speed is 250 m/s but radar could calculate the speed to be anything between 83 m/s to 416 m/s depending on error direction in two detections. Radar would naturally calculate the speed over say 10-20 detections, but then any acceleration or deceleration by the target would instantly create pretty large error until the tracking algorithm could follow. That is when radar does not miss any detections (not very uncommon especially in low frequency radars) and smoothly tracks the target. If it misses just one detection, the uncertainty volume instantly multiplies.
Basically low frequency radar is fine for targets flying straight and level at constant speed, but maneuvers and changes in speed are serious problem for them. That's why they are used for early warning and general surveillance and not for missile guidance.
element1loop wrote:Below wavelengths of about 1 meter (FM) propagation is altered by things like ducting, curvature of Earth, temperature difference, topography and/or building reflection scattering or reverberation that affects directionality of signals. With VHF (6 meter) and OTHR HF bands (<10 meters) you also have the continuous dynamic variation in properties of the Ionosphere, altering signal quality, gain and range resolution.
That can be calibrated and corrected for via having active beacons (providing soundings) or else pulse reflectors (such as a small island or reef outcrop) situated all across the footprint region of an OTHR, so the returned HF signal can be corrected for with input from these known locations of emitters and reflectors. Thus improving the contact location accuracy as conditions alter, and also informing what the conditions are, and how they're changing, when, where, and by how much. Thus how much to correct and interpolate for across the whole region. The result is the OTHR data can remain usefully accurate even with degraded conditions.
So could you likewise do the same at VHF wavelengths using the precisely known locations of disposable or else recoverable drones whose location you do know during every pulse update, and act as VHF emitter beacons or reflectors right across the scan volume of your VHF radars. Thus improving the calibration accuracy against a detected VLO bogie?
Thus the drones use SATCOM to transmit their own 3D-location and their vector, to inform every pulse returned back to the radar's processor, to separately calibrate each regional return pulse with the known beacon location data.
Now add a second or even third VHF radar to provide coverage of the same scan volume from other viewpoints for better combined angular resolution on any VLO bogie contact. Now a pulse hits the contact every 2 seconds, so any dropped pulse does not degrade location track much, it is quickly recovered, and all three radars are able to sharpen their accuracy using the drone locations and vectors, and their own triangulation of these sharper calibrated returned signals from each radar.
Then fuse and resolve a higher-resolution location for the VLO bogie.
Seems to me the location and likely vector (range) of the bogie is going to be significantly improved by doing that.
Then you get the nearest F-35 to launch a MALD to approach the VLO bogie and try to obtain a relative precision position for it. This location with respect to the MALD's known location is then relayed back via SATCOM, or else is embedded with in its own VHF beacon pulse or datalink and is relayed to all other drones, all other MALDs, and to all VHF radars, and all other F-35s.
So the nearest flight of 4 x F-35A now approaches in wide-open formation (another backs it up) towards the most likely area and they do a combined 4 x EOTS level IRST scan of the sky to locate and PID the VLO bogie(s), before the bogie(s) can counter-detect the F-35s or else eliminate the MALD. The bogie could then try to avoid the MALD, but the MALD follows and converges on it, or else a 'loyal wingman' does it.
It seems to me VHF is going to quickly lead to MALD detection/location then an EOTS PID, and a target-grade IRST data stream, for a high-PK passive BVR launch and fly-out, against a declared Bandit that doesn't necessarily know it's been engaged, or even targeted yet.
I think that is how an OPFOR would seek to exploit VHF EW ground systems and J-20 against an F-35 flight, but which VHF radars would be a very high-priority target and a (relatively) immobile system, so a very temporary anti-stealth capability would exist in the opening minutes, that could potentially engage an F-35 ... until jamming occurs.
falcon.16 wrote:I have a doubt, if for example, we can use a VHF radar and we have for example a adquisition box of 3-4 kms on accuracy, is it impossible to guide a missile enough near for in terminal phase the internal seeker radar of the missile to track and engage the stealth target?
S-300 have very big missiles which maybe have enough big radar seeker for helping to VHF radar in terminal phase to track himself the stealth fighter...
Of course, we do not know exactly which data russian missile seekers have...but maybe 4-5 kms detection range against VLO is possible.
There is some inconsistency in cited error bounds for target tracking. This chart shows worst case performance (range error = 200 m; azimuth error = 0.5° and elevation error = 1.5°), with the best case range error at 100 metres and best case azimuthal error at 0.3°. This performance is of the same order as the S-band 64N6E family of PESAs used as SAM battery acquisition radars
The goal with an EPR of 0.1 m2 (the combat unit of an RCBM or a ULTR) can be detected at a range of 600-650 km, and 0.01 m2 - 300-350 km.
Users browsing this forum: No registered users and 5 guests