Chapter 891 Multi-Band Phased Array Antenna
"From a signal processing algorithm perspective, that's certainly true."
Chang Haonan took two steps back and stared at the blackboard for a few seconds before answering:
"But shouldn't this be known before...?"
Wang Xiaomo's question was a bit beyond Chang Haonan's expectations.
Because he had not expected that the other party or other researchers in the field of radar engineering would focus on this.
"Before?"
Wang Xiaomo turned to look at the blackboards where he had just talked about, with some confusion in his tone:
"But you haven't written anything related to this model expression before?"
"No...I'm not talking about this before."
Chang Haonan waved his hand:
"I mean... before today."
“Isn’t it common knowledge that the mathematical model of an optically controlled phased linear array…or any linear phased array, includes three vectors?”
This question did not receive a response.
But it’s not difficult to see the answer from Wang Xiaomo’s eyes——
"Could it be?"
"hiss……"
Chang Haonan originally thought that he had just derived a model expression when the independent variables were known.
The result is that tall buildings rise from the ground...
If it were left to the world of theoretical mathematics, then if he wanted to get the complete process, he would have to prove that "the model only contains three vectors".
Fortunately, the engineering field doesn't really care about these minutiae. As long as it matches the actual situation, it won't be a big problem.
Therefore, after this short interlude, Chang Haonan's introduction went on smoothly.
However, what follows is much more logical in comparison...
“The pulse signal sent by the radar system will be affected by factors such as target scattering and propagation path during the propagation process, resulting in the time domain and frequency domain broadening of the echo signal. Therefore, in order to improve the resolution, the echo signal needs to be pulse compressed. This process is usually done in the time or frequency domain using matched filtering or correlation signal processing..."
Talk as you go, and occasionally add some extra content on the blackboard.
Finally, after more than an hour, he came to the last blackboard.
At this time, Wang Xiaomo's pen had already stopped.
Compared with the previous part, although the latter half is larger in terms of pure calculation, it is much easier to understand because there is no such exaggerated jump.
This also gave him more time to think about some issues in the field of radar engineering.
"..."
"...Through convolution, the pulse compression output result of the array can be obtained from the above formula: s(t), after matching the matched filter, the output is s'(t)=∑(n=1, N)e^(jφ ){e^[j2π(f(t-(t0-τ))+u(t-(t0-τ))T)-e^(j2πf(t-(t0-τ)))]}......"
Chang Haonan pointed with his finger to the lower right corner of the blackboard, the end of all the calculations.
Then he turned around, took two steps forward, and sat back at the conference table.
Then I opened the laptop that had been on the table from the beginning but had never been opened:
"Based on this model, I conducted numerical simulation calculations on the pulse compression of the optically controlled phased array and the fully phased phased array under a typical situation."
He turned the computer 180° and pushed it in front of Wang Xiaomo:
"It can be seen from these two result graphs that the maximum value of the pulse pressure of the fully phase-shifted phased array is 4.21dB lower than the maximum value of the optically controlled delay array. In other words, the signal-to-noise ratio has been lost by 4.21dB."
"In addition, the 4dB width of the pulse pressure of the sub-array delayed optical array is 5.12ns, the side lobe height is -13.84dB, and the peak time position is 49.9989μs; while the 4dB width of the pulse pressure of the fully phase-shifted array is 7.088ns, and the side lobe height is -13.84dB. The lobe height is -26.32dB and the peak time position is 49.9952μs.”
"Therefore, the main lobe of the LFM signal in the fully phase-shifted array is broadened after the pulse pressure, the peak time position deviates greatly, and a certain signal-to-noise ratio is lost. In addition, the spectrum structure of the broadband LFM signal of the fully phase-shifted phased array is no longer a rectangular distribution. , which results in lower-than-expected resolution after pulse compression.”
Staring at the realistic normalized amplitude-time curve on the computer screen, Wang Xiaomo did not speak immediately.
There is no doubt that from the results obtained by Chang Haonan, the optically controlled phased array has mechanical advantages that traditional phased array radar cannot match.
Especially in the field of wide-angle scanning that he had been paying close attention to before.
While waiting for the computer to turn on and open the document for a few minutes, Wang Xiaomo had already roughly calculated several results on his notebook.
It is conservatively estimated that thanks to the broadband characteristics and low loss of optical fiber TTD, the available scanning angle of the single-sided optically controlled phased array will be expanded to ±75° or even ±80°.
This is a huge improvement for fixed single-sided or double-sided array antennas.
but……
Not big enough.
Almost as soon as he saw the simulation results on the computer, he had a more radical idea.
"Mr. Chang."
Wang Xiaomo put the ballpoint pen aside:
"What if we don't pursue expanding the scanning angle?"
"ah?"
Chang Haonan was stunned by this question.
You said you needed a wide-angle scan before, and I calculated the results for you, but now you don’t need it anymore?
What's going on?
Seeing the ghostly expression on his face, Wang Xiaomo quickly continued to explain:
"What I mean is that since the scanning angle and instantaneous bandwidth are a pair of contradictory indicators, then since the optically controlled phased array radar can achieve a large scanning angle with the same bandwidth, can we also change the idea and achieve the same scanning angle with the same bandwidth? high bandwidth?”
After hearing this idea, Chang Haonan lowered his head and pondered.
Then he frowned slightly.
Then his eyes flashed.
"It should be...ok!"
After all, he is not a radar major, and the calculation just now was only a theoretical derivation from the mathematics and physics levels, so his ideas on the application level are actually a bit limited.
When he was in Nanzheng before, Wang Xiaomo had been talking about the problem of wide-angle scanning, so his calculation results had been advancing in this direction.
But now that he was reminded by the other party, his thoughts immediately opened up——
Radar bandwidth and network bandwidth are not the same concept.
It is not a unit of speed but a unit of frequency.
It refers to the frequency bandwidth that the radar antenna can adapt to under normal working conditions.
We often say that a radar "works in a certain band".
This band range is the bandwidth.
In most cases, the back-end module of the radar does not matter the frequency band.
But the adaptability of the transmitting/receiving antenna is very poor.
Therefore, it will generally exhibit narrowband characteristics.
However, as Wang Xiaomo just said, optically controlled antennas can completely overcome this problem.
China's main equipment in the future, whether it is an early warning aircraft or a rotatable double-sided/single-sided array of a ground guidance system, or a four-sided array used on a warship, the demand for wide-angle scanning can be summed up as "it's best if you don't have it." ".
But broadband is another story.
To exaggerate, it can even achieve dual-band or even multi-band detection through the same front!
"If the scanning angle is kept at 120° or 90°."
Thinking of this, Chang Haonan pulled the computer back to him and started typing on the keyboard quickly.
The complex simulation process just now was naturally completed on a supercomputer. Here is just a screenshot of the results.
But just by calculating the bandwidth and scan angle, the performance of the PC is still sufficient.
As time passed, Wang Xiaomo, who was sitting opposite, finally lost his temper and walked around the desk to come behind Chang Haonan, hoping to see the results as soon as the calculation was completed.
A series of calculation commands were entered by Chang Haonan, but the calculation process itself did not last long.
The results were quickly displayed on the computer screen.
"Well... the broadband performance in different bands will actually be somewhat different."
Chang Haonan read it quickly and then concluded:
"In general, for the S-band and adjacent frequency bands commonly used in search radars, if the search range is controlled at ±60°, the frequency range can probably cover about 2.7Ghz, which is basically a complete frequency band plus a less Complete band.”
"If the range is adjusted to ±45°, the frequency range can cover the 3.7Ghz level, which is two complete frequency bands, or one complete band plus two less complete bands..."
"If the frequency range is higher, the available width will be slightly lower. For example, for the X-band, which is common in fire control radars, even if the scanning range is controlled at ±45°, it can only cover 2.9Ghz..."
Wang Xiaomo clenched his right hand into a fist and lightly knocked on his chest.
Obviously, this result is a bit too surprising for the old comrades.
After calming down for a while, he said:
"It doesn't matter. Fire control radar has higher requirements for resolution. I'm afraid the pursuit of a large bandwidth is not as meaningful as a large scanning angle. We should focus on the search radar."
"For example, the sea-based 346 radar, which has almost completed testing, operates in the S-band, but the guidance and command system of the Haihongqi-9 air defense missile works in the C-band. Originally, we planned to install an additional set under the main radar array. Transmitting and receiving antennas, but if the radar can be made to work in S-band and C-band at the same time, this problem can be omitted..."
Chang Haonan, on the other hand, thought more long-term:
"The ship-based four-sided array only needs a working range of ±45°, so that the radar can even work in the three bands of L, S and C at the same time, such as 1Ghz to 4.7Ghz. In this way, the 346 radar can even be directly used to replace the 517A radar, and a certain degree of Anti-stealth and ultra-long-range detection capabilities..."
517A is the model with an antenna shaped like a clothes rack on the back of the 052C/D destroyer. It is an old-timer that has been in service from the 1950s to the 21st century.
Although the overall performance has lagged behind, due to the nature of the P-band, it still has certain anti-stealth and remote warning potential.
This is incomparable to pure S-band radar in principle.
So until the later 052D and even 055, they were constantly changed and continued to be used.
But if the 346 radar itself can work in the L-band, which has similar properties to the P-band, then the demand for 517A will be greatly reduced.
Wang Xiaomo and Chang Haonan looked at each other and saw the huge potential of this technology in each other's eyes almost at the same time.