Counterstealth radars

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michaelemouse

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Unread post05 Jun 2019, 23:43

hornetfinn wrote:Sure long wave radars have better ability to detect stealth aircraft. In the F-117 shootdown in 1999 the VHF P-18 managed to detect the F-117s at 30 km away or closer. P-18 can detect regular small fighter at about 120-160 km away at the altitude the F-117 was flying. So the stealth properties definitely affected that VHF radar significantly.

So yes such low frequency radars can be useful for early warning because high frequency radars are more affected by shaping and RAM. Problem is that such low frequency radars are large and rather expensive and prone to jamming and hard kill measures due to their size and high power transmissions.



Low-freq radars also have the disadvantage that even if you can see the enemy, you know what type of unit it is, you have a pretty good idea of its range, speed etc. That doesn't mean your missile is going to hit. You need frequently updated precise targeting data if you want to hit something from 50km away while that something is trying to avoid dying and then kill you. I'm not sure a targeting quality track could be had with VHF or UHF radar. The impression I get is that it would be like trying to shoot someone with a rifle at 300 meters by hip-firing. It's romantic in its enthusiasm.

I understand why low-freq radars would have higher SWAP requirements than high-freq ones and be more vulnerable to hard-kills but why is it more prone to jamming? I would have thought their large size and high power transmissions would give them an edge so there's something I'm not getting.
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hornetfinn

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Unread post06 Jun 2019, 06:55

michaelemouse wrote:I understand why low-freq radars would have higher SWAP requirements than high-freq ones and be more vulnerable to hard-kills but why is it more prone to jamming? I would have thought their large size and high power transmissions would give them an edge so there's something I'm not getting.


That's mostly because the frequency range is significantly smaller and jamming power does not need to be spread over large frequency range. For example VHF frequency range is only 270 MHz (30 to 300 MHz) whereas X-band frequency range is 4000 MHz (8 to 12 GHz). So 10 kW jamming power would mean only 2.5 Watts for each MHz in X-band case and 37 Watts in VHF case meaning about 15 times higher effective jamming power. So comparatively low frequency radar will be more affected by jamming if similar power levels are used.

Another thing is that there will be a lot lower number of VHF radars than say X-band radars in the battlefield. So jammers can concentrate on smaller number of threat radars which will further increase the jamming effects.

Larger size and high power does give some advantages in jamming resistance which will counteract those above things somewhat. But still low frequency radars will likely be more affected by jammers.
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michaelemouse

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Unread post06 Jun 2019, 20:20

hornetfinn wrote:
michaelemouse wrote:I understand why low-freq radars would have higher SWAP requirements than high-freq ones and be more vulnerable to hard-kills but why is it more prone to jamming? I would have thought their large size and high power transmissions would give them an edge so there's something I'm not getting.


That's mostly because the frequency range is significantly smaller and jamming power does not need to be spread over large frequency range. For example VHF frequency range is only 270 MHz (30 to 300 MHz) whereas X-band frequency range is 4000 MHz (8 to 12 GHz). So 10 kW jamming power would mean only 2.5 Watts for each MHz in X-band case and 37 Watts in VHF case meaning about 15 times higher effective jamming power. So comparatively low frequency radar will be more affected by jamming if similar power levels are used.

Another thing is that there will be a lot lower number of VHF radars than say X-band radars in the battlefield. So jammers can concentrate on smaller number of threat radars which will further increase the jamming effects.

Larger size and high power does give some advantages in jamming resistance which will counteract those above things somewhat. But still low frequency radars will likely be more affected by jammers.



That's a good explanation, thanks. I hadn't thought about it in terms of Jamming power divided by the number of MHz in the relevant frequency bands. Frequency hopping can only take you so far when you have a limited number of hopping options.
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