AESA as part of EW system

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hornetfinn

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Unread post14 Jan 2015, 14:32

It's well known that AESA radars have been also been designed to act as part of EW system. Mostly this has been thought to be very narrowband capability as even current AESA radars are fairly narrowband systems (maybe few GHz total bandwidth). I've been thinking that AESA radars should have far larger bandwidth for EW purposes than for radar purpose as it's receive- or transmit-only as opposed to transmit-and-receive and certain other reasons . When looking through some radar related patents, I came across this very interesting patent from Westinghouse Electric Corp. (they should really know this stuff) filed almost 30 years ago:

http://www.google.com/patents/US4823136

The transmit-receive cells are fully functional at broadband and narrow band radio frequencies. In the narrow band of 9.2 to 10.2 GHz, the active antenna system would operate as a radar system. In the broadband range of 2.0 GHz to 20.0 GHz the active antenna system is fully functional in electronic countermeasures and radio frequency jamming.


This would suggest that AESA radars can actually work as very broadband EW antenna for both ESM and jamming purposes.
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KamenRiderBlade

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Unread post14 Jan 2015, 16:10

How big with the TR modules have to be to support that range of frequencies?

What type of platform would be carrying them?
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hornetfinn

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Unread post15 Jan 2015, 14:51

I think we can assume that T/R modules are optimized mainly for radar frequencies and in fighter radars that’s currently X-band. Modern AESA radars usually have about 1-3 GHz total bandwidth using GaAs technology. Let’s say the radar has 3 GHz total bandwidth and that’s centered on 10 GHz. That means the radar uses frequencies between 8.5 and 11.5 GHz. The T/R module spacing is usually about 0.6 times the highest frequency wavelength. That would result in about 1 wavelength spacing when using 20 GHz. This means that jamming 20 GHz would work well in about ±30 degree sector. It could likely receive over larger sector.

At lowest end 2 GHz the spacing would be close to 0.1 times the wavelength. That would result in quite serious mutual coupling effect when two adjacent modules are transmitting or receiving (although the effect is much more severe in transmission). Mutual coupling would result in lower efficiency and loss of power. There are research papers that show that even with 0.1λ (maybe even 0.05) these losses can be kept at fairly low level with proper design. Still the power output would suffer compared to normal operating frequency. Of course there would still be a lot of power available compared to current fighter internal or podded systems. The jamming power could also be much more precisely transmitted in very tight beams, so the ERP (effective radiated power) of the system would be very high in comparison to older systems.

IMO, it’s likely that for example AN/APG-81 (or any other really modern AESA designed also for EW) can operate effectively as an EW antenna at least in that 2-20 GHz range. It’s possible that it could operate even over larger frequency range but at the expense of power and/or transmission angle. I see the value of NGJ or similar jammer pods especially in the potential to be used against the low frequency radars (UHF and VHF) more effectively. Otherwise radar system should be very capable of used against enemy radars.
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KamenRiderBlade

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Unread post16 Jan 2015, 07:02

On a slightly different note, why would the Brits use a rotating AESA on their new carrier?

Wouldn't a large fixed AESA be better than a rotating AESA?

And on rotating radars, why have only transmitters / receivers on 1 side, why not on two or 3 or more sides.

Is the cost that much greater to add more transmitters / receivers, or is there some sort of technological / physical phenomenon that would cause interference?
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hornetfinn

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Unread post16 Jan 2015, 12:16

KamenRiderBlade wrote:On a slightly different note, why would the Brits use a rotating AESA on their new carrier?

Wouldn't a large fixed AESA be better than a rotating AESA?

And on rotating radars, why have only transmitters / receivers on 1 side, why not on two or 3 or more sides.

Is the cost that much greater to add more transmitters / receivers, or is there some sort of technological / physical phenomenon that would cause interference?


I think the main reason is cost. With rotating AESA antenna you save money on T/R modules, processing requirements, power requirements and thus also weight and space requirements. Another reason is what's the main purpose of said radar. In carriers it's for long range air surveillance and not for engaging enemy aircraft or missiles. For that the relatively slow target update time is not much of a hindrance. An advantage of such rotating single antenna is that it can be installed higher up than fixed systems or at least it's much easier because of lighter weight and lower space requirements. This of course gives somewhat longer distance to radar horizon.

Usually rotating radars have only one antenna face, but there are some radars with two antenna faces also like Sampson used in UK Type 45 destroyers:
http://www.baesystems.com/product/BAES_021434?_afrLoop=1133009282973000&_afrWindowMode=0&_afrWindowId=null#!%40%40%3F_afrWindowId%3Dnull%26_afrLoop%3D1133009282973000%26_afrWindowMode%3D0%26_adf.ctrl-state%3Digynsuvd4_158

Russians have also shown similar arrangement to be available for Pantsir S1 AD system, although it's unclear what's the current status of the system.

There is no other reason besides cost, complexity, weight and power requirements for having only one antenna face for rotating AESA (or PESA) antennas.
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hornetfinn

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Unread post16 Jan 2015, 13:31

If somebody read the patent I mentioned in first post, it's referred to from another very interesting patent describing a missile AESA radar seeker (also from Westinghouse Electric Corp., filed in 1990).

http://www.google.nl/patents/US5061930

It describes using such seeker for both active- and semiactive missile guidance and also for jamming of enemy radars. That patent seems to have antiship missiles in mind, but it might be that future AAMs will have their own jamming capabilities to spoof enemy radar systems. Of course that capability would increase costs of missile systems and IIR based missile warning and tracking systems might make that capability less useful. Other use might be using small UAVs with similar small AESA arrays as expendable jamming systems to overcome powerful defenses. How about SDB II like weapon or future ARM with capability to jam the enemy radar systems (like SAM radars) that are protecting the targets?

With AESA facing AESA I see the electronic battle getting really high intensity compared to most current capabilities. Current jammers will be almost ineffective against AESA radars and AESA jamming making most current (MSA and PESA) radars extremely vulnerable. Of course those capabilities will take a long time before widespread use because of costs and complexity.
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KamenRiderBlade

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Unread post16 Jan 2015, 19:33

I'm wondering when somebody will develop a AAM that has dual Radar / IR seekers in 1 head with thrust vectoring vents like the CUDA.

If you can design a missile like that, your PK for that missile goes up.

Add in remote course correction, it'll be next to impossible to avoid unless you use something like a anti-missile missile where a tiny missile deploys to counter said missile or have active IR lasers strong enough to destroy missiles protect fighter aircraft in a 360 spherical manner like the F-35's DAS system.
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Unread post24 Apr 2016, 12:54

Quick question, do PESA and AESA radars still use Pulse dopler shift to guage range?
Reportedly, sudden "breakstop" maneuvers can hinder the dopler shift returns and cause an aircraft to be momentarily invisible to a radar lock.

Im sure the PESA and AESA systems have moved passed this, but what meathod do they use now? Will a motionless hovering target be invisible to these types of radars?
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basher54321

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Unread post25 Apr 2016, 12:49

zero-one wrote:Im sure the PESA and AESA systems have moved passed this, but what meathod do they use now? Will a motionless hovering target be invisible to these types of radars?


If talking about a helicopter the fast moving rotor blades have always been an issue.

Maybe something like STAP combined with some of the AESA advantages.
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Unread post25 Apr 2016, 13:51

zero-one wrote:Quick question, do PESA and AESA radars still use Pulse dopler shift to guage range?
Reportedly, sudden "breakstop" maneuvers can hinder the dopler shift returns and cause an aircraft to be momentarily invisible to a radar lock.

Im sure the PESA and AESA systems have moved passed this, but what meathod do they use now? Will a motionless hovering target be invisible to these types of radars?


Yes they do, although they don't gauge range but rather to gauge relative speed (closing or receding) of the target. Doppler shift is used to differentiate target returns (which are usually moving) from ground returns which are static (and can be huge in number and strength).

AESA (and to lesser degree PESA) have several things that make that tactic less workable than against legacy MSA radars. As mentioned, STAP is probably the most advanced technique available to detect targets from ground and can make radar almost imprevious to such tactics. STAP has been implemented in both PESA and AESA radars. ESA radars can also use many other tricks as they can revisit detected targets often and can vary frequency, bandwidth, PRF and other such parameters very quickly and this makes them less affected by the tactic. In addition sensor fusion will make the tactic very likely to fail as for example IRST sensors don't get confused with the tactics and radars in other friendly fighters will likely also keep tracking as it's very difficult to fool many widely separated radars at once.
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jetblast16

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Unread post25 Apr 2016, 15:17

' sudden "breakstop" maneuvers can hinder the dopler shift returns and cause an aircraft to be momentarily invisible to a radar lock'

The "beam maneuver" can momentarily render a target invisible to another aircraft's pulse doppler radar if it has a velocity gate; that is, a minimum return speed. This typically involves flying perpendicular to the other aircraft's radar, until your relative velocity falls below its 'velocity gate' (a speed threshold for eliminating--ignoring--unwanted ground clutter or returns).
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