Chapter 548: Clutter is not impossible to deal with

Apart from the tactics themselves, the Air Force and the Defense Work Committee were extremely interested in another matter.

——Move the radar into the sky.

The topic of the seminar gradually shifted from leapfrog tactics to the Tu-4 special aircraft's aerial blind spot filling.

"Comrades, in this operation, when the enemy aircraft entered the blank area controlled by the ground radar station, the Tu-2 special aircraft originally used to attack the P-4V played a very good role in filling the blind spot. This method greatly improved our combat initiative and control of the airspace. So this time, we also want to see if we can do more in this regard."

When everyone heard this, they thought it made sense and started to speak up.

In particular, the comrades who had attended several previous related meetings with Gao Zhendong had long admired Gao Zhendong's idea of ​​"radar into the sky" and had given it more thought.

"Well, this is a good idea. Comrade Gao Zhendong mentioned this idea before. If you ask me, not only radars, but also commanders and so on can go up to the sky together."

"Yes, an airborne command post. With a few planes like this, we can control the coastal areas tightly. If we deploy a few more inland as a mobile force, the enemy will have nowhere to hide no matter where they come from."

"But radar is a problem. Do we have such good radar?"

"We don't have many Tu-4s in total. If we use them all for this, we won't have any heavy bombers left."

"For radar, you can consider using an imitation of the old Russian Conus radar. With a 7-meter antenna, the Tu-4 may still be able to carry it."

The Connus radar is the one that was originally placed on the Tu-4 early warning aircraft. As a radar that can simultaneously measure distance, direction and altitude, it should be the radar with the best overall performance we have at this stage within the size and weight restrictions. However, this radar has a weakness.

"There is no need to consider the quantity of Tu-4s. The main thing to consider is whether its performance is sufficient." At this time, the "Sixth Master", who was about to use up all the English letters, was already in the process of being produced domestically.

Moreover, the Tu-4 is more suitable for this task than the Tu-16 because it can stay in the air longer under the same conditions. It is outdated as a bomber, but it is quite sufficient as an early warning aircraft.

Even if the Tu-16 cannot take over in the short term, it is not a big problem. For domestic combat targets in the short term, the Tu-4 and Tu-16 are actually a bit mediocre.

Especially the Tu-4, which is few in number, flies slowly, has a short range, and a small payload. It is useful as a deterrent, but in actual combat, it is probably just like that.

"The Conus-like radar is good, but its ability to handle ground clutter is limited." A comrade who should be working on radar pointed out the biggest problem of the Conus-like radar in one sentence.

This was also the biggest reason why our first-generation early warning aircraft eventually died. The original scientific researchers tried their best and finally solved a series of problems including engine modifications and huge changes in aerodynamic shape, allowing the aircraft to carry a 7-meter diameter and 2-meter thick antenna cover and fly steadily in the sky.

But in the end, the poor anti-ground clutter performance of the Connus radar made all these efforts come to naught.

"How poor is the ground clutter handling capability of the Conus-like aircraft?" asked the Air Force comrade.

The comrade thought for a moment and replied, "We have never put this radar into the air, but according to theory and experience, it will fail if it is below XXXX meters."

The four-digit failure altitude instantly made the Air Force comrades lose interest. The days of the P-2V wreaking havoc had not been long gone, and the ground clutter problem was still fresh in their memory.

In fact, the radar's reliable "look and shoot down" capability still existed as an advanced function on radar until the 80s, which shows how troublesome it was.

Looking at the faces of the air force comrades, Gao Zhendong raised his hand: "Comrades, I do have some opinions on this issue."

After hearing his words, many people immediately became excited. This comrade always had a clear point. If he said he had an opinion, it meant there should be some solutions.

Especially for the comrades from the Defense Work Committee and the Air Force, Gao Zhendong's "opinion" was extremely important to them.

Seeing everyone looking at him, Gao Zhendong said, "First of all, I think it is not meaningless to send the radar into the sky, even if we cannot deal with ground clutter for the time being. At least we have a means of early warning for targets coming from high altitudes. Generally speaking, targets coming from high altitudes are very threatening and common at this stage."

When the comrades in the Air Force heard this, they thought it made sense. They had also considered this, but still felt unwilling to accept it. Other comrades, on the other hand, felt that Gao Zhendong's idea of ​​solving the problems that could be solved first was feasible.

"Well, that makes sense. Low-altitude targets are invisible to ground radar anyway, so at least we should control the high-altitude targets first."

"Well, high-altitude and high-speed penetration is the main method of penetration now. Being able to solve this problem is actually not bad."

"But with the popularization of terrain radar, the penetration method is now shifting towards low-altitude penetration."

"Yes, our Attack-5 is designed for low-altitude penetration, even at the cost of sacrificing combat radius." Seeing that everyone had their own ideas, Gao Zhendong added the second half of his sentence.

"Besides, ground clutter is not completely unmanageable."

Comrades were furious at once. They thought that this problem would not be solved in China now, or even in the next 10 or 20 years. They couldn't even come up with theoretical ideas, let alone solve it in actual engineering.

Therefore, Gao Zhendong's words were not a big deal to people outside the radar industry, but his colleagues in the radar industry were almost pinching Gao Zhendong's neck and shouting "Tell me quickly, tell me quickly."

The same goes for the comrades in the Air Force. They are not engaged in radar, but they use radar, so they know very well what this sentence means.

Let alone them, if the Russians heard what Gao Zhendong said, they would have to worship Gao Zhendong. They really solved the ground clutter problem of fighter radars when it came to the MiG-23. Before that, it was just that.

Thinking about it again, Gao Zhendong was the first person who advocated "flying radar into the sky". Maybe he had some idea that led him to make this suggestion.

Everyone stared at Gao Zhendong, but the leader of the Defense Work Committee said something that poured cold water on everyone. Want to listen? Then the scorer.

"Comrade Zhendong, you and the comrades working on radar should go to a branch meeting place nearby. We will discuss other issues here first."

It is not uncommon to have multiple branch venues for a seminar, but it is very rare to have a branch venue temporarily.

Gao Zhendong and the eagerly awaited radar-related comrades, led by the conference staff, came to another small meeting room. Looking at the comrades with eager eyes, Gao Zhendong continued what he had not finished saying just now.

"I have analyzed the signal characteristics of the radar and I think we can use phase detection to indicate moving targets."

Moving target indication (MTI) and moving target detection (MTD) are typical ground clutter processing technologies.

The latter is more effective, but requires higher technical skills, so it’s a little early to use it now.

But MTI can be used.

"Due to the Doppler effect of moving targets, the radar echo reflected by the moving target will shift in phase, while the radar echo of fixed targets such as the ground, hills, and buildings will not have this phase change."

This principle alone confused several comrades at the scene. At that time, they really didn't understand it. Even though they knew about the Doppler effect, which was known for more than 100 years, they didn't know how to use it.

Most explanations of the Doppler effect describe what is directly seen as a frequency shift, but what is implied is that the phase also shifts.

"Then how can we make use of this phase shift?" I couldn't think of it. I couldn't think of it at all.

"By subtracting the previous signal from the latter signal, the stationary ground object signal will be filtered out, while the changing moving target signal will be retained. This is its basic principle. Although there are many defects, it can at least basically solve the ground clutter problem within a certain range."

Knowing that his comrades were still unclear about the specific operation of this thing, Gao Zhendong drew the block diagram of the delay line cancellation filter on the blackboard.

Simply put, the previous radar signal is input into a delay device, delayed for a period of time, and then subtracted from the next signal.

Using a delay device actually serves the purpose of storing the previous radar echo signal, but the cost of a delay device is much lower than that of waveform storage. This is a very clever design.

After Gao Zhendong said this, the comrades working on radar immediately understood that this was a good idea!
"Boss Gao, this idea of ​​yours is brilliant!"

"Doppler effect, delay cancellation filtering! I never thought of it."

Although he is not a radar major, time domain and frequency domain analysis of signals was a professional basic course in Gao Zhendong's previous life. With this foundation, plus the basic knowledge of downward-looking and downward-firing radar that he looked up during network alignment, he has no problem explaining an MTI.

"However, this method has obvious flaws. The target distance is clear, but the target's motion state is very vague. To a certain extent, it can only indicate whether a moving target exists, but it knows nothing about the state of the moving target. This is why I call it moving target indication - it can only indicate. Of course, there are also some flaws that are restricted by other boundary conditions. For example, the slower the target, the more difficult it is to detect."

MTI has many flaws, but it has one advantage: the technical requirements are much lower than those of MTD, and it can be done without a computer and does not involve in-depth digital signal processing, which is not the case with MTD.

By the way, the MiG-23 uses MTI.

For Gao Zhendong, MTI is not good enough, but for comrades working on radar, this thing is very good!
This is not satisfactory enough, you want to go to heaven, Mr. Gao!
(End of this chapter)