Chapter 620: Reverse Card?

If the signal generation problem has been solved, then what remains is the signal detection and processing. The detection can be done with certainty as long as the signal power is large enough.

Then finally, there is another one.

"But our signal processing technology is very weak, and we don't have much to do with the signal itself. We can use your DJS-60D to calculate the processed signal results, but it can't solve the fundamental problem of target detection."

Signal processing technology is the real stumbling block.

Gao Zhendong was not panicked about this.

"In this way, with a good signal source, we can walk on two legs, one is analog, and the other is digital. I know a little about both aspects."

In fact, Gao Zhendong is more familiar with digital signal processing, which he can directly and brute-force obtain the desired results by piling up computing power. To some extent, by piling up hardware math coprocessors, the ready-made algorithms he has are easier to use than analog circuits.

However, there is a problem in digital signal processing that has not yet been solved, and that is high-speed AD. Generally speaking, when a signal is converted into analog-to-digital, the sampling rate needs to be more than 10 times the signal frequency in order to obtain better waveform data.

This is a very severe challenge for existing devices, and it is very troublesome even if other signal preprocessing operations are performed first.

As for direct sampling and full digital processing, although this kind of thing is cool, it is nothing but a fantasy for current devices, so don't even consider it.

Therefore, Gao Zhendong's idea is to walk on two legs. When digital processing cannot be done in a short time, it is also possible to use analog circuits for Doppler processing. At least the analog Doppler processing of the APG-4 of the F-59J has a good effect.

At least it is much stronger than the MiG-23, and it is on the same level as the F-5J five years later, so it is not bad.

As for radar principles, Gao Zhendong had collected some information in his previous life out of personal interest, especially the PD radar, which was not the latest but had a wide range of applications. When phased array technology was still being kept secret, PD technology content was relatively easy to find.

The knowledge from the technological environment decades later would be a real dimensionality reduction blow if applied to today.

With the principles of radar and the corresponding technical means of analog processing, Gao Zhendong still had some knowledge. But he should not forget one thing, that is, courses such as signals and systems, and time domain and frequency domain analysis of signals were his professional courses in his previous life.

With the knowledge from the previous life and the brain of this life, it is not a problem to explain the principles to everyone. With these targeted theoretical knowledge, I believe these comrades will have their own ways.

It's like the guy who works in HIFI. He may not understand the real principles, but if you ask him to build a tent, he can do it very well.

Seeing that Gao Zhendong was confident, and considering that the Defense Work Committee had already tacitly approved of this radicalism, and even in order to cover up the possible consequences of this radicalism, the Defense Work Committee strongly retained the RP-1 imitation work.

Since these big guys dare to take a gamble, there's nothing wrong with him following suit.

In case PD fails, it won't be a problem to use the intermediate results of PD to make a low-spec radar with single pulse + moving target indication. There is nothing to be afraid of. This thing is definitely better than the imitation RP-1.

The traveling wave tube proposed by Gao Zhendong gave him great confidence. As the saying goes, great power can produce miracles. Now that he has great power, he might as well look forward to a miracle.

The comrades who bear the main responsibilities are brave enough to fight and fight hard. It would be incompetent if we just hide in the back. Besides, they are not completely unprepared. They have taken everything into consideration, from devices to theories.

Don’t be fooled by people who say “I know a little bit” modestly. In fact, what they mean is “Don’t be afraid, I will teach you.”

"Okay, in that case, we'll do it according to PD Radar." Mr. Liu made up his mind that it would be great if this cross-generation could be achieved.

The young people who came with him were also ready to go. They were definitely the group that rushed in the most fiercely, roaring and yelling. They were determined to do something big if they were going to do it.

They watched as Gao Zhendong rejected most of the plans that they had been thinking about for a long time, but they didn't seem unhappy at all. They were still very angry.

"Chief Engineer Gao, everything is almost ready. Take a look at this antenna..."

Gao Zhendong burst out laughing, leaving Mr. Liu confused. Is this antenna thing funny?
Gao Zhendong didn't know how to explain it either, mainly because he remembered the famous meme from his previous life - "the inverted card artifact", and he couldn't help it.

The inverted Cassegrain antenna comes from the antenna structure used by the Russians from the MiG-21 to the Su-27. In fact, this thing is also used by others, such as John Bull's Tornado, and many ship radars also use it.

The reason why only the Russians came up with this joke is mainly because we use it a lot and we don't use it well. Mr. 8 has been trying to develop the card-reversing artifact for decades without success.

In addition, the Su-27's basic radar is large and heavy, and its parameters seem to be off the charts, but its actual BVR capability is at the bottom of our third-generation aircraft. Not to mention other things, even the unused Block 2 can rub it. So the unhappy domestic military fans gave it this nickname.

The reason why Gao Zhendong was so happy was not because Mr. Liu used the inverted card antenna this time. In fact, it was precisely because he did not use the inverted card antenna, but used the father of the inverted card - the Cassegrain antenna.

It is estimated that although the space in the nose of the aircraft has increased a lot, the high focal diameter ratio requirement of the parabolic antenna is still not good for combat, so he chose the Cassegrain antenna with a relatively low focal diameter ratio requirement.

However, the Cassegrain antenna was not actually used for a long time on fighter jets and was replaced by an inverted Cassegrain antenna. The main reason was that the signal center was blocked and the sidelobe level was high.

The inverted card solves the problem of the Cassegrain antenna. What's interesting is that if someone who doesn't know much about radar sees the complete inverted card antenna, there is a high probability that he will mistakenly think that it is a phased array.

In fact, it is impossible to use this thing as a phased array antenna. Instead, there is another type of antenna that can realize the phased array capability, that is, the flat slot antenna.

Although the plate gap looks like a flat plate, it is actually mostly formed by many waveguides put together. It is a bunch of independent tubes. If the signal part is well designed, it can indeed realize the principle of phased array, but the number of units may not be too large.

Having said that, as a fairly popular antenna form in second-generation aircraft, the performance of the inverted card antenna is still good at this time. Before the birth of the flat slot antenna, this was considered one of the antenna structures with the best overall performance for fighter jets.

But it started to fall behind after the 90s and even after 2000. The reverse card of the second-generation aircraft is really a magic weapon, and the third-generation aircraft that still uses the reverse card is a bit of a magic weapon.

However, the inverted card can really be used on PD radar, as the antenna and radar system have little to do with each other.

Gao Zhendong had no idea how to explain Mr. Liu's puzzled look, so he got straight to the point: "Nothing, nothing, I just remembered something else. So, Mr. Liu, why don't we use an inverted Cassegrain antenna here?"

This is where Gao Zhendong was confused. If he remembered correctly, the RP-1 radar that General Liu copied earlier, the one installed in the middle of the air intake with a range of "up to" 3 kilometers, used an inverted card. He should not have been unaware of this. Gao Zhendong had seen photos of that thing in his previous life and could tell it at a glance. Its features were too obvious.

Mr. Liu smiled and said, "The RP-1 uses a reverse card, and its performance is too poor, so we use this one."

Gao Zhendong originally wanted to suggest using the inverted card first. After all, the poor performance of the RP-1 radar had nothing to do with the inverted card antenna. The inverted card was more suitable for use on fighter jets than the Cassegrain. The reason why that thing couldn't see far was purely a matter of technology and size. However, when the words came to his lips, he held back because something moved in his heart.

Let’s talk about this matter later. Anyway, no matter whether you use the positive card or the reverse card, it will not have much impact in the end.

I have said no enough, and it would not be good to say no again.

"Well, that's how it is...antenna...let's leave it like this for now." Gao Zhendong said vaguely.

Mr. Liu probably understood something of what Gao Zhendong meant, but seeing that Gao Zhendong didn't say anything else, he just left it alone for the time being.

"Then, Chief Engineer Gao, I will revise this first and send it to the Defense Working Committee?" Mr. Liu, who had gained a lot, put away the notebook.

Gao Zhendong nodded: "Well, let's do it as quickly as possible. The Gong-5 multi-purpose model is making very good progress now. It would be a pity if there is no good radar in the end."

Judging from the feedback from the Cifei Factory, they are making good progress and things have been generally going smoothly so far.

If research and development in later generations was extremely time-consuming, then in this era, the speed of research and development is relatively much faster, because the technology is not so complex, precise, and extreme, and the progress of research, manufacturing, and testing is much faster.

After seeing off Mr. Liu and his companions, Gao Zhendong flipped through a set of drawings.

If you only look at the outer shell picture, you can see that it is a rectangular box with a basically square cross-section, and it doesn't look very big.

This is exactly the thing he and Mr. Liu mentioned just now, the traveling wave tube.

He did not find a traveling wave tube design that would reach the most advanced level decades later, but he was able to find one that met the conditions of the current era or was slightly ahead of others.

The good thing about this thing is that it can exchange size for performance, but Gao Zhendong did not make it too big. He had some other ideas. Using great force to create miracles is one way, but he has his own considerations on how great the force should be.

After checking them carefully, he packed all the drawings into bags and sealed them. He called a comrade from the confidential room of the Third Factory and asked him to send the drawings to the Defense Work Committee and ask the comrades from the Defense Work Committee to select a relevant professional factory to produce a batch on his behalf.

At the same time, Gao Zhendong specifically pointed out that the production plant of this thing has requirements for the personnel structure. In addition to meeting basic confidentiality requirements, there cannot be comrades from foreign countries.

(End of this chapter)