Chapter 890: A Lesson for Academicians
The first half of April was generally calm.
After proving through the principle prototype that picosecond-level pulse laser can indeed achieve controllable non-thermal processing, the most important thing is naturally to start producing an engineering prototype.
Since the specific application environment and hardware layout must be taken into consideration, the engineering prototype cannot be simply put up on a shelf like the principle prototype.
It’s about getting as close to the final product as possible.
This also means that the production process will be longer.
Especially some of the equipment needs to be ordered from abroad.
The efficiency of European companies can only be said to be understood by everyone.
So, Chang Haonan’s project at hand has also entered a tepid stage.
But this is not a bad thing.
After the work intensity of the entire project team decreased, he finally got the opportunity to discuss the idea of "phase control of antenna array elements by photoelectric signals" with Academician Hou and Huo Penghua.
In the end, several people came to a unanimous conclusion.
At least in principle, the idea of optical beamforming networks is feasible.
What Chang Haonan wants is this "possible in principle".
The following problems of system model and system theory can be solved by him.
Going forward, the Electronic Technology Group will worry about the specific implementation.
Originally, Chang Haonan was planning to go to Luzhou in person.
As a result, I called and learned that Academician Wang Xiaomo was going to Beijing for a meeting at the end of April.
It just saves you the trouble of traveling.
……
Although it is not a serious meeting, it is still a serious academic exchange, and it is definitely not appropriate at the dinner table.
So, Chang Haonan simply chose the meeting place in the conference room of the main building of the New Torch Laboratory.
“You chose this place well.”
After getting off the car, Wang Xiaomo tightened her leather jacket, looked around and commented:
“The environment is good , not far from the city, but not too noisy.”
"It's a place for academics."
Although most of the Fifth Ring Road in Beijing was open to traffic at this time, it was still a bit desolate overall.
However, it gave the Torch Laboratory a bit of a paradise feel.
Chang Haonan himself is very fond of this place, so he is not modest:
"How do you say that...far from the academic circle, but close to the academic circle, so to speak This is the kind of place.”
"This is the first time I have heard this statement."
Wang Xiaomo followed Chang Haonan up the steps of the main building:
"But the summary is indeed in place..."
< br>"..."
Walking and chatting along the way, the two soon arrived at the door of the conference room on the top floor.
As early as a few days ago, Chang Haonan had already started preparing the necessary information here.
So, when Wang Xiaomo pushed the door open, he saw at first sight several blackboards filled with formulas and circuit model diagrams.
This situation should have been more suitable for PPT.
But it is too troublesome to make PPT.
Leave it to students to do, but students don’t understand.
You can't let Academician Hou work as a coolie for him, right?
So, Chang Haonan simply got lazy and moved over all the blackboards that he had written down during the discussions and calculations a few days ago.
"This is..."
Suddenly in a sea of mathematical symbols, I am afraid that even Newton or Gauss would be confused for a few seconds.
However, Wang Xiaomo was mentally prepared after all, and recovered quickly. "Last time we met in Nanzheng, I guessed that there must be something hidden in your kid's head..."
While he found a seat with a good view and sat down, he half-jokingly said to Chang Haonan:
“Come on, let’s see what new tricks our manager Chang has come up with! "
Looking at Wang Xiaomo who was already ready to take notes, Chang Haonan took off his coat and then loosened the top button of his shirt:
"This is what I heard last month. I just came up with a new idea after you introduced it.”
As he spoke, he went straight to the first blackboard:
“You told me in Nanzheng that when the phased array radar performs wide-angle scanning, the radar’s transit time and aperture effect will change. As a result, the instantaneous bandwidth of the signal is limited, and sub-array delay or unit phase-shifting structures need to be used to improve this problem. However, the real-time delay lines of traditional microwave waveguides or cables have large losses, strong dispersion, narrow frequency bands, and are bulky and bulky. It’s still beyond the standard.”
“I just happened to be working on a laser processing project recently, which uses optical fiber links to replace cables to transmit signals, so I was thinking about whether optical fiber can also be used in radar.”
Wang Xiaomo holds his chin with one hand and taps rhythmically on the cover of his notebook with a ballpoint pen in his other hand.
This is his habitual action when thinking.
"Simply using optical fiber for TTD is not a particularly new idea."
While Chang Haonan finished his sentence, Wang Xiaomo slowly said:
"I know about 10 Years ago, the American company Hughes tried this method, but there were too many photoelectric conversion processes in the middle. In the end, it was said that there was an extra 40 decibels of signal loss, and it was abandoned in the end.”
But. Chang Haonan had already guessed that the other party would mention this case, and nodded immediately:
"I have also found information on the project you mentioned."
"However, although they used optical fibers for TTD, the process of switching each delay channel still used an electrical switch consisting of multiple lasers plus an n1:n2 fiber coupler plus multiple photodetectors. Each switch structure is To create a total of 32 photoelectric conversion processes of 4*8, it is inevitable that the noise will be high.”
Hearing Chang Haonan hit the point directly, Wang Xiaomo’s hand holding the pen stopped:
“ So... can you solve this problem?"
"Of course."
The former smiled:
"So I thought, since we have already considered using fiber optics, it is better to go all the way to the end and build the entire back-end into a set of optical beam forming networks, and finally use photodetectors to demodulate and recover radio frequency or microwave signals to emit electromagnetic waves. In this way, only one electro-optical-electric conversion process is needed to realize an optically controlled phased array radar..."
At this point, Chang Haonan turned back and pointed to the blackboard behind him:
"For example The switching of the delay channels just mentioned can be purely optical, such as fiber Bragg reflection grating, fiber dispersion prism, or spatial light path switching. In short, there are many ways to completely avoid those 32 groups of photoelectric conversion..."< br>
“Using the light control array directly... can avoid this loss problem”
Wang Xiaomo didn’t know when he had sat up straight:
"But that involves a new theoretical system... If nothing else, there is a big difference between the delay models of optically controlled arrays and electronically controlled arrays."
"This happens to be me The part I’m good at.”
Chang Haonan was already excited and strode to the second blackboard:
“Let’s use a relatively simple one-dimensional line array first. As an example. ”
“Assume that the number of units contained in each sub-array is ns=N/M, then each unit can be expressed as ail, where i is the sub-array serial number and l is the antenna unit inside the sub-array. Serial number, in the actual array, each sub-array is configured with a delay unit that can provide 2^b1 time shift units. Each unit in the sub-array has a b2-bit phase shifter, which is used to complete the phase range of 0-2π The phase shift..."
"For any direction θ in space, the spatial time difference between any adjacent units is τ=dsinθ/c, and for the operating frequency f, the corresponding phase difference is φ=kdsinθ..."
"..."< br>
When it came to this point, Wang Xiaomo had already opened his notebook to a blank page and started recording it vigorously——
Although he was not from a theoretical background, it was not difficult to see that Chang Hao Nan is constructing a mathematical model of a light-controlled time-delay phased linear array.
With a little promotion, it can become a planar array model.
"The phased array antenna can not only be regarded as a spatial domain filter, but also a time domain filter whose transfer function varies with different spatial directions. Suppose the signal input to the first unit of the uniform linear array is s(t)= e^(jωt), then the transfer function of the optically controlled phased array in the pointing direction is H(ω)={Msin[ns/(2c)]dsinθ0(ω-ω0)}/[sin{(1/2c) ]dsinθ0(ω-ω0)}..."
As the explanation gradually progressed, Chang Haonan began to add some new content to the blackboard from time to time.
Some of them were omitted and not written down at the time, and some were newly thought of during the calculation process.
The structure of the entire mathematical model gradually became clear.
“Swish, swish, swish…”
Wang Xiaomo wrote down the last character on the current blackboard as quickly as possible, and then stopped writing.
Judging from the total number of blackboards in this conference room, Chang Haonan's introduction is probably only about half done.
However, he can now see a lot of valuable information from it.
“In other words, you only need to determine three key values: the spatial delay operator vector of the array, the beam pointing phase shift vector within the array, and the delay operator vector within the array, to complete the design of the optical control array. Signal model simulation? "
This is obviously much simpler than his or any estimate other than Chang Haonan's.
In other words, even from an engineering perspective, this idea of using photoelectric signals to control phase differences for scanning is fully potential to be realized!
(End of this chapter)