Chapter 890: Teach the Academicians a Lesson

The first half of April was generally calm.

After proving that picosecond pulse lasers can indeed achieve controllable non-thermal processing through the principle prototype, the most important thing is naturally to start producing an engineering prototype.

Due to the need to consider the specific application environment and hardware layout, the engineering prototype cannot be simply built like the principle prototype.

Instead, it must be as close to the final product as possible.

This also means that the production process will be relatively long.

In particular, some of the equipment needs to be ordered from abroad.

The efficiency of European companies can only be said to be understood by those who understand.

Therefore, 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 was reduced, he finally got the opportunity to discuss the idea of ​​"phase control of antenna array elements by optoelectronic signals" with Academician Hou and Huo Penghua.

In the end, several people came to a unanimous conclusion.

At least in principle, the concept of optical beamforming network is feasible.

And what Chang Haonan wants is this "principle feasibility".

He can solve the problems of system model and system theory later.

And the specific implementation level will be taken care of by China Electronics Technology Group.

Originally, Chang Haonan was going to Luzhou in person.

But he called and found out that Academician Wang Xiaomo would go to Beijing for a meeting at the end of April.

It just saved him the trouble of traveling.

…

Although it was not a serious meeting, it was at least a serious academic exchange, and it would definitely not be appropriate to have it 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 a good place."

After getting off the car, Wang Xiaomo tightened his 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 made the Torch Laboratory look like a paradise.

Chang Haonan himself also likes this place very much, so he is not modest:

"How does that saying go... Far from the academic circle, but close to academia, this is what it means."

"This is the first time I've heard of this saying."

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

"But the summary is indeed very accurate..."

"..."

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 materials here.

Therefore, when Wang Xiaomo pushed the door in, he saw several blackboards filled with formulas and circuit model diagrams at first glance.

This situation should have been more suitable for PPT to play.

But making PPT is too troublesome.

Give it to students, and students don't understand.

You can't let Academician Hou do hard labor for him, right?

So, Chang Haonan simply took a break and moved all the blackboards written during the discussion and calculation process a few days ago.

"This is..."

Suddenly being in a sea of ​​mathematical symbols, even Newton or Gauss would be stunned for a few seconds.

However, Wang Xiaomo was mentally prepared and recovered quickly.

"Last time in Nanzheng, I guessed that you must have something in your head..."

He found a place with a good view and sat down, and said to Chang Haonan half-jokingly:

"Come on, let's see what new tricks our President Chang has come up with!"

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

"This is a new idea that I thought of after listening to your introduction last month."

He went straight to the first blackboard:

"When you told me in Nanzheng, phased array radar is in the process of entering When scanning at wide angles, the transit time and aperture effect of the radar will lead to the limitation of the instantaneous bandwidth of the signal, and it is necessary to use subarray delay or unit phase shift structure to improve this problem. However, the real-time delay line of traditional microwave waveguides or cables has large loss, strong dispersion, narrow bandwidth, and excessive volume and total volume. "

"It just so happens that I am working on a laser processing project recently, which is to use optical fiber links instead of cables to transmit signals, so I wonder if optical fiber can also be used on radar. "

Wang Xiaomo held his chin with one hand and tapped the cover of his notebook with a ballpoint pen in the other hand.

This is his habitual action when thinking.

"Using optical fiber for TTD is not a particularly new idea."

While Chang Haonan was finishing his sentence, Wang Xiaomo slowly said:

"I know that Hughes Corporation in the United States tried this method about 10 years ago, but there were too many photoelectric conversion processes in the middle, and it was said that there was an extra 40 decibels of signal loss in the end, and it was finally abandoned."

Chang Haonan had long guessed that the other party would mention this case, and nodded immediately:

"I have also found information about 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... you can solve this problem?"

"certainly."

The former showed a smile:

"So I thought, since we have already considered using optical fiber, 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..."

Having said this, Chang Haonan turned back and pointed at 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 light 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 completely sat upright:

"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 the part I'm better 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..."

"..."

When he got to this point, Wang Xiaomo had already opened his notebook to a blank page and started 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 phased linear array.

And 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 on the blackboard from time to time.

Some were missed and not written down at the time, and some were newly thought of during the calculation process.

And 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 was 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!