Chapter 666: Try this, it's awesome

If the signal-to-noise ratio can be improved by 20 dB, then the problem caused by splitting the traveling wave tube into two will no longer be a problem.

Between a little bit of weight and volume loss, plus a slightly increased system complexity, and such a huge improvement in signal-to-noise ratio, anyone who is not a fool would know what to choose.

One of Mr. Liu's subordinates suddenly had an idea: "Chief Engineer Gao, can we increase the number of traveling wave tubes to get a higher signal-to-noise ratio?"

Gao Zhendong shook his head: "That's not necessary. The reason for splitting it into two is that there are only two important nodes in this structure, and it happens to be split and opened at these two positions. If more nodes are added, the cost will be more than worth it. Under this indicator requirement, this signal-to-noise ratio is enough, and too much is as bad as too little. But if possible, we can consider other ways of splitting it. We will talk about this later."

The comrade understood and nodded while taking notes.

Gao Zhendong turned around and looked at Mr. Liu: "How are the simulation results using the Cassegrain antenna?"

Speaking of this, Mr. Liu shook his head somewhat bitterly: "Just like what you suggested at the time, it seems that we still have to use the inverted card antenna. Simulation calculations show that the central lobe performance of the Cassegrain antenna is too poor, while the side lobes are thriving."

Mr. Liu is well aware that the simplified conditions and optimal theoretical calculations are so bad that the actual machine results will generally be even worse.

The Cassegrain antenna was quickly eliminated and rarely used in fighter radars. The reason is that the output signal characteristics are really not good, which is even worse for fighter radars, which are already limited in size and weight and have limited output power.

Although the emergence of the traveling wave tube improved the signal source, they knew that the maximum possible value was 10, but due to the Cassegrain antenna, they only achieved 6, which was unacceptable to Mr. Liu and his colleagues.

Even though we later made fun of the "inverted antenna" every day, in fact, the inverted antenna was indeed a good antenna solution in that era, otherwise the Russians would not have always used it on the Flanker. The "Tornado" fighter jointly developed by John Bull and Hans Cat also used this in the early days.

"Fortunately, the problem was found during the theoretical simulation stage, and not much time was wasted. We are going to design an inverted card antenna, which, theoretically, will be much better." Mr. Liu still feels very lucky.

The beauty of the inverted card antenna is that although it seems that there is a reflective surface in front blocking the radar waves, in fact, the two reflective surfaces twist the polarization direction of the signal, just like polarized light. The first reflection of the reflective surface in front is all reflected back to the second reflective surface. After the second reflective surface reflects and twists the polarization direction of the signal, it can penetrate the first reflective surface and be emitted unimpeded.

Gao Zhendong nodded and said with a smile: "Well, your idea is good, but I have an antenna here, you might as well take it back and test it before deciding which one to use."

After saying that, he opened something that he had prepared before the meeting.

When Mr. Liu and his team took a look, it looked a bit like a signal reflection surface of an inverted card antenna, but they could not tell where the feed source was, nor could they see any obvious signal reflection transmission path.

On the back of this "antenna", there is a general waveguide interface, which is the interface for the signal output from the traveling wave tube.

Small gaps can be seen on the surface of the antenna. After a closer look, several comrades realized that this thing looks like a flat plate, but is actually made up of thin tubes.

"Chief Engineer Gao, what is this?" Mr. Liu was a little puzzled. This thing was really new and he had never seen it before. But Chief Engineer Gao certainly couldn't be joking with everyone.

Gao Zhendong pointed at the antenna and said, "This is a sudden idea of ​​mine. It's called a flat slot antenna!"

Flat panel gap? After thinking about it, this name is really very descriptive!
It looks like a flat plate with gaps running through it.

In fact, the simplest flat slot antenna is just a metal plate with many slots on it. It’s just that the antenna is too simple, and Gao Zhendong feels that it is a bit mediocre.

When Mr. Liu heard the name, he knew the secret might be in these gaps. He estimated with his eyes and thought about it in his head, and seemed to have figured out a solution.

"Chief Engineer Gao, the signal from this antenna is transmitted through these small gaps? I see that the size of these gaps seems to be exactly half of the wavelength of the radar we use."

Gao Zhendong gave a thumbs up: "As expected of a CEO, that's it."

The reason why Gao Zhendong did not bring this thing up before was because he was not sure whether he could make it.

He did have a very detailed paper on flat slot antennas, but after all, that paper was about X-band antennas, and the radar they were planning to develop was C-band, which could take into account both search and guidance, but had a longer wavelength than the X-band. In this technical environment, it was easier to do something.

How to change the X-band antenna to C-band is the problem facing Gao Zhendong. The knowledge searched out is different from the items extracted from the system store. There is no adaptive modification. Advanced is advanced, and sometimes, this advancement is a trouble.

Gao Zhendong made the first version of the flat slot antenna, actually a long time ago. The last time Mr. Liu and his team came, the first version was already almost there, but there were some performance issues, and Gao Zhendong has been making improvements.

This process was still a bit difficult. After all, he didn't major in this field. No matter how smart he was, he had to digest all the knowledge in the paper before he could figure it out.

He digested and improved it at the same time. After so long, it was finally close. The theoretical calculation indicators were very good, and the only thing left was the actual machine test. However, the third factory did not have the conditions for this actual test, so it had to be sent to General Manager Liu. After saying this, he took out a calculation manuscript: "Strictly speaking, this can be called a broadband waveguide slot antenna. The slot is made on the waveguide tube. These waveguide tubes can be regarded as linear array antennas, and then they are combined into a flat slot antenna."

Mr. Liu has very sharp ears and heard some key elements right away.

"Linear array? Combination? Chief Engineer Gao, what do you mean? Array?"

Chief Engineer Gao is planning to do something big. He wants to make a phased array?
This is the reason why Gao Zhendong did not develop a pure flat slot antenna. The waveguide slot array can actually realize the phased array to a certain extent.

Although it cannot be compared with the active phased array with a large number of T/R units, as a fighter radar, compared with the later traditional passive phased array, the gap between the properly designed waveguide slot array and it is not particularly large.

Because this thing is essentially a simple phased array.

Gao Zhendong smiled and shook his head: "Let's test it first. This is the design result of theoretical calculation. We don't know whether it can be realized or not. Let's test it first."

Haha, I see. Chief Engineer Gao is not being cautious and does not want to reveal his ambition too much. Chief Engineer Liu took over Gao Zhendong's calculation manuscript and looked through it in conjunction with the antenna entity.

"I was wondering why the two gaps are different. It turns out that they realize polarization in two directions..."

"Center frequency 5.3GHz, bandwidth 0.4GHz? Am I reading this correctly?"

Gao Zhendong smiled and said, "It's called broadband waveguide slot antenna. If we don't make the bandwidth bigger, wouldn't it be unworthy of the name? The bandwidth range of the traveling wave tube is already large. If we don't make the antenna bandwidth bigger, wouldn't it be a waste?"

Mr. Liu nodded, then shook his head. He said, "No, no, no. Chief Engineer Gao has all these tricks."

"Vertical and cross polarization are lower than -40dB, and horizontal polarization linear array mutual coupling is lower than -20dB. Not bad, really good..."

Mr. Liu, who had been talking to himself, suddenly raised his voice: "The difference between the first side lobe and the main lobe signal is 15dB!!"

Mr. Liu suddenly felt like a serf who had risen from the dead and was singing. The unsatisfactory spatial distribution of radar signal energy output had always been a major problem that troubled them, and was basically at the same level as the gain.

Parabola, Cassegrain, inverted card, all these twists and turns are just to ensure these performances.

Then Chief Engineer Gao quietly came up with an antenna with such an ideal energy distribution and a certain phase control potential.

For Mr. Liu, let alone phased control or electronic scanning potential, even if there is no electronic scanning capability, the main and side lobes of the radar signal are enough!

"Boss Gao, is this true?"

Gao Zhendong did not guarantee it: "This is the theoretical calculation. You have to test it yourself to know the specific situation. But the probability of success is very high. I am still quite confident."

This is nonsense. This thing will not be used too much in the future. Before phased arrays became popular, this thing dominated the market for high-performance fighter radars.

Mr. Liu was so happy: "Mr. Gao, let's go back and try it now."

Gao Zhendong smiled and said, "You guys give it a try. If it succeeds, you can consider reducing the rated power while keeping the gain the same, making the traveling wave tube smaller, and then dividing the linear array into several groups, using different traveling wave tubes to drive different groups of antennas..."

Mr. Liu slapped his thigh and said, "I understand! This is phase control!"

Isn't this a phased array? No wonder Chief Engineer Gao just mentioned that there are other ways to group traveling wave tubes. It turns out that it was prepared for this purpose.

Gao Zhendong nodded and smiled, "Yes, although this can only achieve electronic scanning in one direction, and the other direction still needs mechanical scanning, but at least one direction can be scanned quickly. Considering that the electronic scanning angle of this method may not be particularly large, it is recommended that the antenna retain mechanical scanning capabilities in both vertical and horizontal directions."

Mr. Liu nodded repeatedly: "Yes, yes, yes, this way, the functions of searching and tracking and multi-target scanning will have a basis for realization, haha."

He smiled very happily.

(End of this chapter)