Excellent illustration I will use to explain one of the many advantages of an AESA system over the current mechanically actuated dish/planar systems.
In the current mechanically actuated dish/planar system, the radar beam have a binary mode: on/off.
As the beam sweeps, the radar is in automatic search or surveillance operation. If the pilot turns the radar off, he is EM blind. He cannot surveil his area of watch, track suspects, or lock his weapons. For the current mechanically actuated dish/planar system, search/surveillance is the default operation. If the pilot switches to track, the search/surveillance operation does not go away. It is still there and is the foundation for track and lock operations. What happens is that the track operation draws upon the data of the search operation and the lock operation draws upon the data of the track operation.
The problem of resource allocation now occurs.
To put it simply, speculate that the system have 100 mb of memory. The search operation uses 50 mb. If the pilot select track, the remaining 50 mb is allocated to tracking and the more targets the pilot assigned to track, the less memory will be available per target. This often leads to target track lost even if the target or targets are within beam view. Keep in mind we are looking at 3D space dynamic targets here. This is why designers of the mechanically actuated dish/planar systems places memory limits, hardware and software based, on each mode of operation with search consuming the highest.
Target resolutions are:
- Altitude
- Speed
- Heading
- Aspect angle
Because of these hard memory limits, the granularity of target information varies from designer to designer. For example, instead of 100.001 km/h, the speed resolution is 100 km/h or even coarser. The granularity of the four target resolutions have direct effects on weapons data, as in designing missile guidance/navigation laws. The missile is much smaller than the parent launch aircraft, its resources are less, so if the missile relies on initial targeting information from the parent launch aircraft, the more precise those four target resolutions, the greater the probability of a kill. Resolution of .001 km/h is much better than .1 km/h.
Since search, track, and lock operations are so intricately tied-in to each other in the current mechanically actuated dish/planar system, this relationship is called 'coupling' and the opposite is 'decoupling'...
IEEE Xplore Abstract - Parameter optimisation in phased array radar
The flexibility of a phased array radar together with the decoupling of the search and tracking functions means that there are many more operating parameters compared with conventional track-while-scan radars. Decisions on the values of these parameters have to be made both at the design stage and in a changing operational situation. It is shown that the optimum choice of parameter values can be made which will ensure the achievement of a specified search performance for minimum mean power. The process of optimisation gives rise to powerful design concepts which can also be applied to adaptive radar management in the operational situation.
I try to avoid paywalled sources as much as possible and IEEE membership runs in the thousand$ per. But if I have to use it, I will make sure that the abstract contains the relevant keywords so the readers understand I am not making these things up.
Precisely because of the ability of an AESA antenna to generate true multiple beams, if the AESA system have 100 mb of memory, all 100 mb will be allocated to tracking the target or targets. Target resolutions will increase in granularity, producing much better targeting information to the weapons lock operation. Since there are true multiple beams, there is no need to have a broad and 'noisy' search beam. The result is that in the AESA system, the search, track, and lock operations are completely decoupled from each other, making the system overall more EM 'quiet', in a manner of speaking.
In a PESA system, since there is only one beam, there is no true decoupling of operations. The advantage of the PESA system over the mechanically actuated dish/planar system is that of faster beam direction changes. The PESA designer will have more flexibility but at best, only to half of what an AESA designer can do.
Decoupling operations is a driver in giving an AESA system more computing power and memory. Why only 100 mb ? Why not another CPU and 200 or even 500 mb of memory ? Keep in mind that these numbers are just to illustrate general ideas and operating principles. The exact design parameters are top secret, of course.
Air forces that can afford the AESA and have seen its capabilities under real world conditions are moving towards it. Those who have the cash are dismissing the PESA.