Naval missile guidance thread - SAM systems
- Thread starter Iron Man
- Start date
Might be wrong for me to generalize.
Let me show you modern examples.
Here you see the DAC and ADC right on the card itself along with the FPGA.
So thus what you are illustrating above, is all in now in a single card.
Here is the anatomy of a modern AESA module.
The amps are near the connectors, and the A/Ds are right behind it in one card. This one is simpler, as it doesn't have an FPGA on it.
Let's go back to Phazotron's module for its Zhuk AE. You can see four amps, the ADs on the PCB, and then the FPGA.
We have some problem with the language. T/R module does not necessarily mean this set is entirely on a single card. Often this whole set, which can be better described as a subarray of four T/Rs, is also called a module.
Here is another example.
Something like this is already being made in a single card.
Now this is PESA.
The phase shifters are arranged under the waveguides, and the signal has to be fed and pass through them. There is not much else behind the phase shifters.
Then there are these long lines that feed the signal to the array like this.
You contrast that to the AESA where the AD and DA chips are in the same PCB with the HPA, LNA chips right behind the antenna, and the FPGA doing a lot of other things.
The phase shifters are arranged under the waveguides, and the signal has to be fed and pass through them. There is not much else behind the phase shifters.
Then there are these long lines that feed the signal to the array like this.
You contrast that to the AESA where the AD and DA chips are in the same PCB with the HPA, LNA chips right behind the antenna, and the FPGA doing a lot of other things.
I never said it can work.
What I said there is nothing of it in the applied world.
How many SSPA do you need to cluster to get a desired power? Let's say you want an array that you plan to make a 1mw central amp. You are provided with 500w SSPA to make this cluster. You will need 2000 SSPA then. But there's a problem. The SSPA power isn't going to scale arithmatically, and for every SSPA you add, some efficiency is lost. You might be better off with fewer, more powerful TWT units than having more, less powerful SSPA units.
No, that's not the argument. The point is that you can have a SSPA amplify the signal from a waveform generator before going into the TWTA of a PESA radar. Please read back my original post where I provided a reference to an article from the Microwave Journal.
You claimed that the key to the superior frequency agility of AESA are the SSPA, but failed to explain why.
In fact, a TWTA has by far the largest bandwidth of microwave amps, so it is difficult to understand how a SSPA architecture could beat it in frequency agility.
Yes to boost the signal by cascading with the SSPA, and smoothing out the linearity. This brings up the TWT and VET devices to the same linearity expected of SSPA devices, however you now have the cost and complexity, as well as the increased breakdown points, of having both a VET and an SSPA. I like to see the complexity of power supply that is needed there, with one requiring high voltage at least 1000v, and the other needing at least a 100 amp.
Frequency bandwidth, or frequency variability, is not the same as frequency agility. With solid state you can change state instantaneously, while vacuum or electron tubes, even if they are still agile, there is a bit of a warm up, build up, then deceleration.
Another thing is that with VETs are constantly running at high power, and with LPI you need to shift down to low power.
Do you just make this up as you go?
There are systems since the 1970's that are able to change their frequency on a pulse to pulse basis. The space within which you can frequency hop is restricted by the bandwidth of your HPA.
Therefore, no reason to believe that AESA is in any way more frequency agile than PESA.
Then explain why everyone is going AESA, even the Russians.
I am not convinced about everyone going AESA.
But let's see what we established so far in this thread:
1. Frequency agility: no difference between PESA and AESA
2. Beamforming on receive. Both PESA and AESA can do this.
3. Digital beamforming on receive: both PESA and AESA can do this.
4. Beamforming multiple beams on transmit: only useful in rare circumstances due to severe reductions in PA product. PESA radars with multiple transmitters and subarrays can also do this.
5. Phaseshifter before HPA. Only AESA. Leads to a different, likely cheaper phase shifter that needs to handle much lower power levels. Distinct advantage of AESA due to lower losses on transmit.
6. No corporate waveguide architecture with 0.1dB/m losses. Distinct advantage of AESA
7. Peak power: clear advantage of PESA due to VED HPAs.
Something to discuss further: digital on transmit?
Some things we haven't discussed, and revolve between the choice of SSPA vs VED. While almost all AESAs use SSPA for their HPA, we cannot rule out an implementation using VEDs because the improvement in the technology has reached a point where TWTA can compete in size with SSPA and beat them in overall package volume/weight. That's why they tend to be the better choice for UAVs.
1. Theoretically higher MTBF. This is not always clear cut. SSPA are not as durable as VEDs in space applications for example. They also tend to have more problems with the power supply compared to VEDs. Many times VED based systems turn out to be more durable.
2. No maintenance required for SSPAs. Clear plus.
3. No warmup time. Clear plus.
4. Available manufacturing capacity of SSPAs. Clear plus.
I'm not convinced about that. State changes between a large CRT vs. much smaller device with solid state transistors. LPI also operates on low power. There is also the timing from long feed lines vs. being much closer to the antenna. There is also linearity, and noise power that favors the SSPA, especially the GaN SSPA.
I don't know what "improvement in technology" you are referring to, when much of the defense industry isn't pursuing VED devices, not even the Russians. If you want to use an SSPA upon a TWT to improve linearity, you will end up having another power supply for the SSPA, because TWT requires high voltage but SSPA requires high amp. That's not going to beat a pure SSPA system in terms of heat and weight, since you now also have to cool and power the SSPA added on the TWT. As for heat, shift to GaN means SSPA will be cooler and more power efficient, this means smaller power supply and less obstrusive cooling systems.
TwT are not a universally better choice for UAVs. They are chosen for a specific purpose. TWTs are used with SAR, as SAR often uses extremely high frequencies. That's the advantage of TWT over solid state, very high frequencies over Ka band, and SAR is used for terrain mapping. But SSPA is gradually going pushing this boundary. If you are not going to use SAR, UAVs are moving into conformal arrays, which is a type of AESA that is non planar. These arrays can blend with the body form of the UAV.
A single VED powering a PESA isn't more reliable than more than 1000 elements of an AESA. If the single VED fails, there goes the entire radar. If a single element fails on the AESA, it results only in a tiny degradation of performance. How many elements need to fail all at one time before you achieve significant degradation, and even that, the radar can still function? What are the chances of this happening?
In a naval system, the AESA also allows an engineer to replace a broken module through the back of the array, even during the middle of the sea. This is assuming a fixed type AESA set on deckhouse or an integrated mast. In a naval AESA, with four arrays, you can easily have up to over 20,000 elements alone in a ship in a combined total, let's say with four arrays the size of the SPY-6 or Type 346A.
Here for example, you can access the AESA panels from within to conduct repairs and module replacement.
Still plenty of manufacturing capacity for vacuum tube type amps, especially for microwave ovens.
And of course, an SSPA can be made so much smaller as you can see with solid state HPA and LNA here.
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