The Military-industrial Scientific Research System of the Academic Master Chapter 890

Chapter 890: Teaching academicians a lesson

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 relatively long.

Especially some of the equipment needs to be ordered from abroad.

The efficiency of European enterprises can only be said to be understood by everyone.

Hence, Chang Haonan's project 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 with 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 subsequent problems of system model and system theory can be solved by him.

Going forward, the Electronic Technology Group will be concerned 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 will go to Beijing for a meeting at the end of April.

It just saves you the trouble of running around.

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 out of 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.”

The fifth ring road in Beijing, although most of it is open to traffic at this time, is still a bit desolate overall.

However, on the contrary, it gives 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? It's far away from the academic circle, but close to the academic circle. This is the kind of place you're talking about.”

“This is the first time I've heard this statement.”

Wang Xiaomo followed Chang Haonan up the steps of the main building:

“But the summary is really in place…”

Walking and chatting along the way, the two soon arrived at the door of the conference room on the top floor.

A few days ago, Chang Haonan had already started preparing the required information here.

Therefore, when Wang Xiaomo pushed the door open, he first saw 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 was lazy and moved all the blackboards he had written down during the discussions and calculations in the previous days.

"This is…"

Suddenly being in a sea of mathematical symbols, I am afraid 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 we come up with!”

Looking at Wang Xiaomo who was ready to take notes, Chang Haonan took off his coat and then loosened the top button of his shirt:

“This is a new idea that I only came up with after listening to your introduction last month.”

He said and 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 cause the instantaneous bandwidth of the signal to be limited, and sub-array delay or unit phase shifting needs to be used. structure 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 excessive volume and total weight.”

“I just happened to be working on a laser processing project recently, which is to use 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 held his chin with one hand and tapped a ballpoint pen rhythmically on the cover of his notebook with the 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 speaking, Wang Xiaomo slowly spoke:

“I know that about 10 years ago, the American Hughes Company 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 in the end it was abandoned.”

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 A total of 32 groups of photoelectric conversion processes are required, which means it will be noisy."

Hearing Chang Haonan hit the point directly, Wang Xiaomo's hand holding the pen stopped:

“So...can you solve this problem?”

"certainly."

The former showed a smile:

"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..."

Speaking of this, Chang Haonan turned back and pointed to the blackboard behind him:

“For example, to switch the delay channels just mentioned, purely optical methods can be used, such as fiber Bragg reflection grating, fiber dispersion prism, or spatial optical path switching. In short, there are many ways to completely avoid those 32 sets of photoelectric conversion..."

“Using the light control array directly...can avoid this loss problem”

Wang Xiaomo didn't know when he had sat up completely straight:

“But that involves a new theoretical system... Among other things, the delay models of optically controlled arrays and electronically controlled arrays are very different.”

“This happens to be the part I'm good at.”

Chang Haonan was already excited at this time and strode to the second blackboard:

“Let's first use a relatively simple one-dimensional line array as an example.”

"Assuming 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 serial number inside the sub-array. In the actual array, each sub-array configuration 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 shift in the 0-2π phase range..."

“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…”

By the time he got to this point, Wang Xiaomo had already opened his notebook to a blank page and was writing furiously—

Although he is not from a theoretical background, it is not difficult to see that Chang Haonan is constructing a mathematical model of a light-controlled time-delay phase-controlled linear array.

As long as it is slightly generalized, 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 on 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.

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, we 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 signal model simulation of the optical control array?”

This is obviously much simpler than he, or any other estimate except Chang Haonan.

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)

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