Chapter 666 Try this, this is exciting
It can increase the signal-to-noise ratio by 20 dB, so the problem caused by splitting the traveling wave tube into two will not be a problem at all.
Between a small cost of weight and volume, a slight increase in system complexity, and such a large improvement in signal-to-noise ratio, anyone who is not a fool will know what to choose.
A comrade under Mr. Liu suddenly had a whim: "General Engineer Gao, can we increase the number of traveling wave tubes to obtain a greater signal-to-noise ratio?"
Gao Zhendong shook He shook his head and said, "That's not necessary. The reason why we split one into two is because in this structure, there are only those two important nodes. It just happens to be split and open at these two positions, and if it is increased, the cost will be somewhat outweighed by the losses. Under this indicator requirement, this signal-to-noise ratio is sufficient, but if possible, it can be considered. We will talk about other splitting methods later.”
The comrade understood and nodded while recording.
Gao Zhendong turned his head and looked at Mr. Liu: "You used the Cassegrain antenna, what are the simulation results?"
Speaking of this, Mr. Liu shook his head bitterly. : "Same as your suggestion at the time, it seems that we still have to use it. Card antenna. Simulation calculations show that the central lobe performance of the Cassegrain antenna is too poor, but the side lobes are prosperous.”
Mr. Liu is very clear that the simplified conditions and optimal theoretical calculations are so bad. In this way, the actual machine will generally only make it worse.
The Cassegrain antenna was quickly eliminated in fighter radars and was rarely used. This is the reason. The output signal characteristics are really not good. For the original due to the limited size and weight, the output For fighter radars with limited power, it is even worse.
Although the emergence of traveling wave tubes has improved the signal source, although they knew it could achieve 10, they could only achieve 6 because of the Cassegrain antenna. This was unacceptable to Mr. Liu and others.
Don't look at the fact that we ridiculed the "reverse card artifact" every day. In fact, in this era, the reverse card antenna is indeed a good antenna solution, otherwise Lao Maozi would not have been using it on the flanker. This was also used in the early days of the "Tornado" fighter jointly developed by John Bull and Hans Cat.
“Fortunately, the problem has been identified in the theoretical simulation stage and not much time was wasted. We are going to design a reverse card antenna, and from a theoretical point of view, the effect is much better.” Mr. Liu still feels very lucky .
The wonderful thing about the reverse card antenna is that although it seems that there is a reflecting surface in front of it blocking the radar wave, in fact the two reflecting surfaces reverse the polarization direction of the signal, just like polarized light, and the reflection in the front The first reflection from the surface is completely reflected back to the second reflective surface. After the second reflective surface reflects and reverses the polarization direction of the signal, it can penetrate the first reflective surface and be emitted without hindrance.
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 next to him that he had prepared before the meeting.
When Mr. Liu and the others took a look, it looked a bit like a signal reflection surface of the inverted antenna, but they could not see where the feed source was, nor could they see an 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.
On the surface of the antenna, small gaps can be seen. Several comrades took a closer look and found that this thing looked like a flat plate, but was actually made up of thin tubes.
"General Engineer Gao, what is this?" Mr. Liu was a little confused. This thing is really new and has never been seen before. But Chief Engineer Gao definitely can't make fun of everyone.
Gao Zhendong pointed at this antenna and said: "This is my sudden idea, it's called a flat slot antenna!"
Flat slot? After everyone thought about it, this name is really vivid!
It looks like a flat plate with slits on it.
In fact, the simplest flat slot antenna is really just a metal flat plate with many gaps on it. However, that kind of antenna is too simple, and Gao Zhendong feels that it is a bit difficult to go up or down.
As soon as Mr. Liu heard the name, he knew that the secret might be in these gaps. He evaluated it in his eyes and thought in his head, as if he had come up with some ideas.
"General Engineer Gao, is the signal of this antenna emitted through these small gaps? I see that the size of these gaps seems to be almost exactly half the wavelength of the radar we use."
Gao Zhendong stood up Thumbs up: "As expected of the boss, that's it."
The reason Gao Zhendong didn't bring this up before was because he wasn't sure whether he could make it.
He does have a paper on flat-panel slot antennas, which is very detailed, but after all, that paper is about X-band antennas, and the radar they are planning to develop is C-band, which can take into account both search and guidance. , but the wavelength is longer than the X-band. In this technical environment, it is easier to do.
How to change the X-band antenna to C-band is the question put in front of Gao Zhendong. The knowledge searched out is different from the items extracted from the system store. There is no adaptive transformation. Advanced is advanced. , sometimes, this advanced nature is a trouble.
Gao Zhendong made the first version of the flat-panel slot antenna. It was actually very early. The last time Mr. Liu and the others came, the first version was almost the same. However, there were some performance problems, and Gao Zhendong has been improving it.
This process is still a bit difficult. After all, he is not studying this. No matter how bright his mind is, he has to digest all the knowledge in that paper before he can come up with it.
He just digested and improved at the same time. After making changes for so long, he finally got it right. The theoretical calculation indicators are very good, but what is left is the actual machine test. For this actual test, the No. 3 Factory does not have this condition anyway, and it has to be sent to Mr. Liu and the others. After speaking, he took out a calculation manuscript: "Strictly speaking, this can be called a broadband waveguide slot antenna. The slots are made on the waveguides. These waveguides can be regarded as linear array antennas. Then Then they were combined into a flat slot antenna.”
Mr. Liu’s ears were bright and he heard some key elements at once.
"Line array? Combination? Chief Engineer Gao, what do you mean? Array?"
Chief Engineer Gao wants to build a big one. Do you want to build a phased array?
The reason why Gao Zhendong did not build a pure flat-panel slot antenna is here. The waveguide slot array can originally realize a phased array to a certain extent.
Although it cannot be compared with active phased arrays with a large number of T/R units, as a fighter radar, compared with later passive phased arrays in the traditional sense, a properly designed waveguide slot array is comparable to The difference is not particularly big.
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. We will wait until we test it."
Haha, I understand, Chief Engineer Gao. This is Not wanting to be on the safe side and not wanting to reveal his ambition too much, Mr. Liu took Gao Zhendong's calculation manuscript and looked through it combined with the antenna entity.
"I asked why the two gaps above are different. It turns out that they realize polarization in two directions..."
"The center frequency is 5.3GHz and the bandwidth is 0.4GHz? I didn't Is that wrong? ”
Gao Zhendong smiled and said: "The name is called broadband waveguide slot antenna. If we don't make the bandwidth wider, wouldn't we be sorry for the name? The main reason is that the bandwidth range of traveling wave tubes is already wide. If we don't make the antenna bandwidth wider, Isn’t it all in vain? ”
Mr. Liu nodded, then shook his head. It can't be compared, it can't be compared to Mr. Gao's tricks, one after another.
“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 has been talking to himself , suddenly raised his voice: "The first side lobe The difference with the main lobe signal is 15dB!”
Mr. Liu suddenly felt like he was singing. The spatial distribution of radar signal energy output is not ideal, which has always been a big problem for them, and the gain is basically the same. position.
Parabolic, Cassegrain, reverse card, all this tossing and turning is to ensure these performances.
Then Engineer Gao quietly took out an antenna with such ideal energy distribution and a certain phase control potential.
For Mr. Liu, let alone phase control or electric scanning potential, even if there is no electric scanning capability, just the main and side lobes of the radar signal are enough!
"Mr. Gao, is this true?"
Gao Zhendong didn't guarantee it either: "This is the theoretical calculation. What is the specific situation? You have to test it yourself to know. But this success The probability is very high, I am quite confident. "
This is nonsense. This thing will not be used too much in the future. Before the proliferation of phased arrays, high-performance fighter radars dominated the world.
Mr. Liu was so happy: "Mr. Gao, let's go back and try now."
Gao Zhendong smiled and said: "You guys try it, if it succeeds. You can consider increasing the gain at the expense of reducing the rated power." No change, make the traveling wave tube smaller Then divide the linear array into several groups and use different traveling wave tubes to drive different groups of antennas..."
Mr. Liu slapped his thigh: "I understand! This is phase control!"
Isn’t this just a phased array? No wonder Chief Engineer Gao just said that there are other ways to group traveling wave tubes. It turned out to be prepared for this matter.
Gao Zhendong nodded and smiled: "Yes, although this can only achieve electrical scanning in one direction, and the other direction still needs to be scanned by machine, but at least one direction can be scanned quickly. Considering this The electrical scanning angle of the method may not be particularly large, and it is recommended that the antenna retain organic scanning capabilities in both vertical and horizontal directions.”
Mr. Liu nodded repeatedly: "Yes, yes, in this way, the functions of tracking while searching and multi-target scanning will be realized, haha."
He smiled very happily.
(End of this chapter)