How AESA radar work (theory) ?

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laos

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Unread post26 Apr 2014, 01:39

A typical fire control AESA radar on a fighter have around 1000 MIMIC chips. Each chip can emit and receive electromagnetic impulses. Is it possible then that AESA radar “paint” a target with each impulse spread among 1000 frequencies ?
If yes, each chip receive only the impulse he emits.
Let's have an example - a clasic radar with 10kw peak power and 150km range to 1m2 target. A Aesa version with 1000 chip and impulse spread on 1000 seperate frequencies shoud have significantly shorter range due to the fact that each chip receive only 1/1000 the energy the clasic version does.
Where is a mistake in my thinking because AESA does not have significantly shorter range?
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Unread post26 Apr 2014, 02:08

Typically, each T/R module is operating at different phases of the same-ish frequency, not on differing frequencies as you said. This shift in phase is how the beam is electronically steered. Additionally, because there are so many emitters, AESA radars have much smaller side lobes than MSA radars.
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Unread post26 Apr 2014, 03:04

A single transmitter emits a broad wave that expands outward in nearly a spherical pattern (probably more of a hemisphere). It takes a large number of transmitters emitting at precisely set phases to focus the wave into a beam.
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Unread post30 Apr 2014, 08:41

Theoretically it's possible that each T/R module acts as an own radar, so that each one uses different frequency and works independently from other T/R modules. This would result in radar that forms huge amount of beams (as many as there are modules), but the effective range would be very small. That kind of radar would not work. So the AESA radar works as others have described and uses all or number of T/R modules in co-operation to create radar beam(s). Beam shape is created controlling the phase of each module so that radar signals created by each module either constructively or destructively affect the beam. Basically the constructive effect is used to create the main beam by most of the modules and some modules "sharpen" the beam by destructive effect. This very precise control of the radar beam is also is why AESA radars have very extremely sidelobes compared to MSA and even PESA radars.

AESA radars have much better range compared to other radar systems as they have much smaller transmission and receiving losses. For example if both AESA and PESA/MSA radar have the transmitter power of 10kW, then the actual transmitted power (in the radar beam) in the AESA radar will be about twice the power in PESA/MSA radar. This is because the transmitter is in the antenna with very little in between in AESA radar. In PESA/MSA radar the transmitter itself is in the back end of the radar and there is a lot more lossy equipment in between it and the antenna. AESA also enjoys similar advantage in receiving the radar signals as the receiving element Low Noise Amplifier is again in the antenna (in T/R modules). In MSA/PESA radars it's located in the back and there are lossy equipment between it and the antenna. AESA radars can usually work with signals that are half the strength required by MSA/PESA radars. Another factor is that AESA radars usually have higher duty factors than MSA/PESA radars. This means that their average power is higher compared to their peak power than in MSA/PESA radars. Average power is the power that affects radar performance, peak power really does not. Other thing is that modern AESA radars can have very high power levels as T/R module technology has improved a lot. I bet APG-81 has higher peak power compared to for example APG-68 or APG-65/73 or even MSA APG-63 or APG-71. It most likely has several times the average power.

All this means that AESA radars have operating ranges that are much better than in MSA or PESA radars. What's more that they can achieve a very large FOV without sacrificing target update times or even range that much. While MSA or PESA fighter radars can search only few hundred square degrees of the sky while tracking targets, AESA radars can search for thousands of square degrees while tracking targets. The net increase in performance potential is huge, but the downside of AESA technology is that they require a lot of software and computing power to work effectively. This is why they are more expensive and development takes quite a lot of time.
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Unread post14 Jul 2014, 08:36

The $10B Next Generation Jammer Is ‘On Track, On Schedule’
14 Jul 2014 Colin Clark

"...Very little has been said publicly by Raytheon or the Navy about the NGJ, its technologies or its capabilities. Yuse continued that trend, very politely. He described the system as covering both offensive and defensive electronic warfare. It is “initially focused heavily on the air-to-ground mission for air defense.”

Perhaps the most intriguing tidbit from our conversation, which occurred July 2, was Yuse’s mention of “an AESA array that can do EW, coms, radar, SIGINT all at the same time.” Most observers know that AESA can handle EW and radar. But there’s been very little public discussion of AESA’s ability to perform Signals Intelligence (SIGINT) or its ability to serve as a communications array. Aviation Week‘s Amy Butler and I asked Lockheed’s head of the F-35 program on Thursday about whether AESA could serve as a communication’s device, and we got the “I’m not sure I can discuss that” answer.

AESA as a communications device makes sense given its digital nature. If you can turn voice into zeroes and ones, then you should be able to send and receive that information.

Initially, the jammer will be installed on the Navy’s dedicated electronic warfare platform, the EA-18 Growler. Yuse said the pods could also be installed on aircraft such as the Navy’s unmanned UCLASS with relatively few changes required: “It is a very flexible design that does not require a lot of aircraft modifications — we kind of refer to it as smart pod.”

The pod includes algorithms with a data library to read the existing threats or targets and to offer responses. Part of the reason few changes are required for new aircraft is that the pod contains virtually everything needed. “From an operational standpoint it’s pretty independent. It’s not very intrusive into the aircraft’s avionics.”

Source: http://breakingdefense.com/2014/07/the- ... -schedule/
RAN FAA A4G Skyhawk 1970s: https://www.faaaa.asn.au/spazsinbad-a4g/ AND https://www.youtube.com/channel/UCwqC_s6gcCVvG7NOge3qfAQ/
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Unread post05 Nov 2018, 21:52

hornetfinn wrote:Theoretically it's possible that each T/R module acts as an own radar, so that each one uses different frequency and works independently from other T/R modules. This would result in radar that forms huge amount of beams (as many as there are modules), but the effective range would be very small. That kind of radar would not work. So the AESA radar works as others have described and uses all or number of T/R modules in co-operation to create radar beam(s). Beam shape is created controlling the phase of each module so that radar signals created by each module either constructively or destructively affect the beam. Basically the constructive effect is used to create the main beam by most of the modules and some modules "sharpen" the beam by destructive effect. This very precise control of the radar beam is also is why AESA radars have very extremely sidelobes compared to MSA and even PESA radars.

AESA radars have much better range compared to other radar systems as they have much smaller transmission and receiving losses. For example if both AESA and PESA/MSA radar have the transmitter power of 10kW, then the actual transmitted power (in the radar beam) in the AESA radar will be about twice the power in PESA/MSA radar. This is because the transmitter is in the antenna with very little in between in AESA radar. In PESA/MSA radar the transmitter itself is in the back end of the radar and there is a lot more lossy equipment in between it and the antenna. AESA also enjoys similar advantage in receiving the radar signals as the receiving element Low Noise Amplifier is again in the antenna (in T/R modules). In MSA/PESA radars it's located in the back and there are lossy equipment between it and the antenna. AESA radars can usually work with signals that are half the strength required by MSA/PESA radars. Another factor is that AESA radars usually have higher duty factors than MSA/PESA radars. This means that their average power is higher compared to their peak power than in MSA/PESA radars. Average power is the power that affects radar performance, peak power really does not. Other thing is that modern AESA radars can have very high power levels as T/R module technology has improved a lot. I bet APG-81 has higher peak power compared to for example APG-68 or APG-65/73 or even MSA APG-63 or APG-71. It most likely has several times the average power.

All this means that AESA radars have operating ranges that are much better than in MSA or PESA radars. What's more that they can achieve a very large FOV without sacrificing target update times or even range that much. While MSA or PESA fighter radars can search only few hundred square degrees of the sky while tracking targets, AESA radars can search for thousands of square degrees while tracking targets. The net increase in performance potential is huge, but the downside of AESA technology is that they require a lot of software and computing power to work effectively. This is why they are more expensive and development takes quite a lot of time.


With Pesa radars the noise figure its around 4-6 db if this picture is correct.

Image

I have a question, if noise figure is 4-6 db, does it mean radar need receive from target more than 4-6 db for get detection?

I think 4-6 db is around 4-5 m2...so any fighter less than 4 m2 RCS would be not detect...ummm, i am very confused about it.
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Unread post05 Nov 2018, 23:00

hornetfinn wrote:Theoretically it's possible that each T/R module acts as an own radar, so that each one uses different frequency and works independently from other T/R modules. This would result in radar that forms huge amount of beams (as many as there are modules), but the effective range would be very small.


Not quite. For an AESA array to be able to steer, T&R modules near each other need to be on the same frequency and sending the same signal. By varying the timing between the modules, the beam can be steered/focused. The more modules that are involved, the better the job of steering. You can split up the array into groups, but each group will need enough modules to steer the beam.

http://www.radartutorial.eu/06.antennas ... na.en.html

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Unread post06 Nov 2018, 08:26

falcon.16 wrote:With Pesa radars the noise figure its around 4-6 db if this picture is correct.

Image

I have a question, if noise figure is 4-6 db, does it mean radar need receive from target more than 4-6 db for get detection?

I think 4-6 db is around 4-5 m2...so any fighter less than 4 m2 RCS would be not detect...ummm, i am very confused about it.


Yes, that's true that in PESA radars the noise figure is significantly higher than in AESA radars. This is because there are more lossy elements in the signal path. This means that in PESA radar the received signal needs to be significantly stronger than in AESA radar to overcome the internal noise.

Decibel is just a ratio (dimensionless unit) and you are thinkin about dBm which is decibel-milliwatts which has reference to milliwatt (a unit). In the picture PESA has noise figure of 3.05 - 0.25 dB = 2.8 dB. This means the received signal from target needs to be almost 2 times higher in PESA than in AESA to be detected. That alone gives AESA almost 20 percent longer range.

One has to remember that the same losses also affect transmit path and the actually transmitted radar signal power is quite a bit lower in PESA than in AESA radar if the power generated by the transmitters is the same. The loss is pretty much the same in transmit path as in receive path meaning that with same transmitter power the AESA will have about 40 percent longer range when both transmit and receive paths are considered.

And that's not all. AESA antennas tend to have higher gain than PESA antennas which means the antenna is more efficient to transmit and collect radar signals. This further improves range and other qualities. Of course current AESA radars can also transmit at higher power levels than best PESA radars and in the future the difference will only get bigger.
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Unread post06 Nov 2018, 09:28

SpudmanWP wrote:
hornetfinn wrote:Theoretically it's possible that each T/R module acts as an own radar, so that each one uses different frequency and works independently from other T/R modules. This would result in radar that forms huge amount of beams (as many as there are modules), but the effective range would be very small.


Not quite. For an AESA array to be able to steer, T&R modules near each other need to be on the same frequency and sending the same signal. By varying the timing between the modules, the beam can be steered/focused. The more modules that are involved, the better the job of steering. You can split up the array into groups, but each group will need enough modules to steer the beam.


Sure. You are talking about practical AESA array and I was just talking about theoretical array with each module acting as independent radar. That theoretical array would not be able to steer the beams and the range woud be incredibly short and other performance figures horrible. Basically totally useless system although possible. In real world radar applications, there would need to be at least several dozen modules forming a single beam to be useful for anything.
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Unread post06 Nov 2018, 17:33

hornetfinn wrote:
falcon.16 wrote:With Pesa radars the noise figure its around 4-6 db if this picture is correct.

Image

I have a question, if noise figure is 4-6 db, does it mean radar need receive from target more than 4-6 db for get detection?

I think 4-6 db is around 4-5 m2...so any fighter less than 4 m2 RCS would be not detect...ummm, i am very confused about it.


Yes, that's true that in PESA radars the noise figure is significantly higher than in AESA radars. This is because there are more lossy elements in the signal path. This means that in PESA radar the received signal needs to be significantly stronger than in AESA radar to overcome the internal noise.

Decibel is just a ratio (dimensionless unit) and you are thinkin about dBm which is decibel-milliwatts which has reference to milliwatt (a unit). In the picture PESA has noise figure of 3.05 - 0.25 dB = 2.8 dB. This means the received signal from target needs to be almost 2 times higher in PESA than in AESA to be detected. That alone gives AESA almost 20 percent longer range.

One has to remember that the same losses also affect transmit path and the actually transmitted radar signal power is quite a bit lower in PESA than in AESA radar if the power generated by the transmitters is the same. The loss is pretty much the same in transmit path as in receive path meaning that with same transmitter power the AESA will have about 40 percent longer range when both transmit and receive paths are considered.

And that's not all. AESA antennas tend to have higher gain than PESA antennas which means the antenna is more efficient to transmit and collect radar signals. This further improves range and other qualities. Of course current AESA radars can also transmit at higher power levels than best PESA radars and in the future the difference will only get bigger.


I understand now, thanks.
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Unread post06 Nov 2018, 20:48

PFM... :lmao:
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Unread post07 Nov 2018, 07:16

hornetfinn wrote:[
Decibel is just a ratio (dimensionless unit) and you are thinkin about dBm which is decibel-milliwatts which has reference to milliwatt (a unit). In the picture PESA has noise figure of 3.05 - 0.25 dB = 2.8 dB.


Uh, this should've been "In the picture PESA has 3.05 (PESA NF) - 0.25 dB (AESA NF) = 2.8 dB higher noise figure (NF) than AESA".
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Unread post07 Nov 2018, 16:13

hornetfinn wrote:
hornetfinn wrote:[
Decibel is just a ratio (dimensionless unit) and you are thinkin about dBm which is decibel-milliwatts which has reference to milliwatt (a unit). In the picture PESA has noise figure of 3.05 - 0.25 dB = 2.8 dB.


Uh, this should've been "In the picture PESA has 3.05 (PESA NF) - 0.25 dB (AESA NF) = 2.8 dB higher noise figure (NF) than AESA".


Yes i understood.

2.8 db better transmitting + 2,8 db better receiving = 5,6 db

It is as 5 times better Aesa range than Pesa Range.
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Unread post07 Nov 2018, 22:40

Resolution not range !
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Unread post08 Nov 2018, 07:34

falcon.16 wrote:
hornetfinn wrote:
hornetfinn wrote:[
Decibel is just a ratio (dimensionless unit) and you are thinkin about dBm which is decibel-milliwatts which has reference to milliwatt (a unit). In the picture PESA has noise figure of 3.05 - 0.25 dB = 2.8 dB.


Uh, this should've been "In the picture PESA has 3.05 (PESA NF) - 0.25 dB (AESA NF) = 2.8 dB higher noise figure (NF) than AESA".


Yes i understood.

2.8 db better transmitting + 2,8 db better receiving = 5,6 db

It is as 5 times better Aesa range than Pesa Range.


Decibel is logarithmic and 5.6 dB means power gain of 3.63 which means PESA needs to transmit 3.63 times stronger signal to achieve similar range performance from internal losses. With equal transmitted (average) power the PESA will have 40 percent shorter range (for example 140 km instead of 200 km).

AESA radars can have much higher average power than equivalent PESA radars and also have more efficient antennas with higher gain. All together means that AESA can have pretty much twice the range of equivalent PESA radar. With GaN technology that performance gap will become even bigger.

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