Chapter 619 What magnetron? No need for that

Simply put, pulse Doppler is a way of transmitting and processing radar signals, but phased array is mainly a way of generating signals, but this generation method can bring many other benefits.

There is no contradiction between pulse Doppler technology and phased array. Using pulse Doppler does not mean you cannot use phased array.

In fact, all phased array radars can use PD technology.

It’s just that these two methods each represent the biggest characteristics of a generation of radar, so they are used to divide radar generations, that’s all.

But the difference between pulse Doppler and phased array is that it is more specific and detailed, so not as many people know about it as phased array.

To give an inappropriate example, everyone knows the word "bird", but many people may not know what birds like "Silly Gugu" or "Xiangxiang Chicken" are.

Even in the 21st century, if you ask a non-military fan what a phased array radar is, they may be able to give a few words, but if you ask them what a "pulse Doppler radar" is, I'm afraid most of them won't be able to tell you.

As an advanced radar that is still under development by the Americans, the first PD radar to be put into use was the one on the F-4J, which did not appear until 5 years later. At this point in time, it is natural that Mr. Liu did not know about the PD radar for the time being.

"You don't know about pulse Doppler (PD) radar?"

"I don't know, Mr. Gao, tell me, tell me."

Mr. Liu immediately became interested. Mr. Gao has a lot of good things here. Maybe he just thinks when he has nothing to do, and he has a lot of wonderful ideas.

In fact, the principle of this radar is easy to understand. As the name suggests, it is a pulse radar that uses the Doppler principle for detection. However, what are the benefits of doing so is not something that Mr. Liu can figure out in a short time.

Gao Zhendong had to introduce the principles and typical applications of PD radar, a pulse radar that uses Doppler ranging. Because it can easily introduce many digital signal processing technologies, and thanks to the strong adaptability of digital signals to various signal processing algorithms, it has strong capabilities for back-end processing of radar signals. Before the emergence of phased array radar, PD was the ultimate answer to solving fighter radar problems.

It can solve the problems of ranging, speed measurement, guidance, downward looking, downward shooting... and the effect is very good.

The phased array radar mentioned here refers to the active phased array. As for the so-called passive phased array, its kinship with the active phased array is not as close as that with the PD radar. It can be regarded as the PD radar with the ultimate development of the antenna.

Of course, this will cause confusion again. The reason is still the same: PD and phased array are the products of two different division methods, and there are places where they can be integrated with each other at their roots.

Therefore, Gao Zhendong is not very interested in airborne passive phased arrays because the cost is too high and the benefits are mediocre.

Of course, not all active phased arrays are good. For example, the Japanese one can only see 37 kilometers, which is not as good as using a whole PD.

After listening to Gao Zhendong's general explanation of the principle, General Manager Liu, who is indeed the top domestic expert in airborne fire control radar, understood the principle roughly, and soon realized that this thing looked good, but...

"Mr. Gao, this thing looks good, but with our current conditions, there are many insurmountable obstacles." Mr. Liu was very calm and objective.

Gao Zhendong nodded: "It should be possible. Tell me about it. I don't have as deep a understanding of the current situation as you do, so your opinions and experience are very important. Let's see if the current conditions can support it."

"Let's put aside the specific signal processing technology for now. Those things are invisible and intangible, and it's hard to explain them in a short time. Let's look at the hard conditions first."

Signal processing technology is the biggest reason why we have been working on PD for decades but have achieved nothing. We simply don’t know what technology, algorithm, or conditions to use to process these signals.

But this technology cannot be explained in a few words, and today’s comrades have no idea how difficult it is. It seems that it can be done by just writing and drawing on paper.

"I just listened to your introduction. It seems to me that the first thing about this thing is that the signal frequency must be accurate, right? Without this basic condition, it is impossible to use the Doppler shift phenomenon to detect the target. If the frequency is not accurate, who knows how much the echo signal has shifted?"

Mr. Liu has a strong ability to identify problems and is indeed very experienced. He pointed out a current situation that Gao Zhendong was unaware of.

"But the reality is that we simply cannot generate a frequency-stable radar signal."

??? Gao Zhendong was confused. He couldn’t even do this?
"No, not even this? Isn't it enough to generate stable frequency oscillation, frequency modulation, power amplification, and then output it through the antenna?"

Hey, you say you don’t know, but you know everything. I say you know, but you really don’t know, Mr. Liu complained in his heart.

"That's right, Chief Engineer Gao. The generation of a stable and accurate oscillation signal has indeed been solved through the phase-locked loop technology you provided, but there are some problems with the power amplification."

Only then did he remember that the problem of generating stable and accurate signals had to be solved by others. No wonder they looked like "how difficult is that?". Perhaps in other people's minds, this was not a big deal.

Thinking of this, Mr. Liu's heart warmed up. A stable signal is of great benefit everywhere, even if it is not a PD radar. Maybe Chief Engineer Gao can help?

"Power amplification?" There are many methods or devices to amplify the power of signals. These methods or devices are alternately rising and developing in a spiral, and are now at a special node.

"Yes, enlarge it. We are using magnetrons now, and they are imported magnetrons."

Magnetron is a signal power amplifier device commonly used in early radars. In fact, everyone has used this thing. One of its civilian branches is called a microwave oven.

Mr. Liu's words fully illustrate the seriousness of the problem. We cannot produce this thing ourselves, but this is not the most serious thing.

"There is a problem with the magnetron. The frequency cannot be accurately made. In addition, due to the existence of the resonant cavity, the frequency is low and the bandwidth is small, making it difficult to output high-power signals in the form of pulses." The problem that Mr. Liu mentioned is the biggest one.

This is equivalent to taking the two basic principles of PD radar: pulse and Doppler shift, and this thing can't do either one.

In other words, it cannot be done now. The magnetron itself is also developing in spiral. Later, some special types of magnetrons could do it, and they were also used in advanced shipborne passive phased arrays. But that is another story. We cannot rely on that thing in the short term.

As an expert in the field of radar, Mr. Liu's analysis is still very accurate and to the point, and his considerations are also correct. This is indeed the first obstacle to becoming a PD at this stage. There is not even a signal, and there is no way to do it at all.

Gao Zhendong listened and said in confusion: "Oh, magnetron, I know. But we don't use magnetron, we use traveling wave tube."

Now it was Mr. Liu's turn to be confused.

“What is a traveling wave tube?”

"Traveling wave tube is..." Gao Zhendong was about to say that this was a power amplifier device developed by the Citigroup guys in the late 50s and early 60s, but suddenly he remembered that something was wrong.

Fuck! I can’t tell you this. The news is not known in China yet. It’s still unclear whether Lubyanka knows about it or not. Otherwise, the radar of the Russian fighter jets wouldn’t be so bad now.

The most advanced Sapphire-21 of the Russians is still a weakling. In addition to the fact that the radar system is still a single-pulse, it is also closely related to the power. If the power is not good, then the power amplifier device will naturally not be good.

Well, I have no choice but to accept this. As for what the Citigroup thing is called, it’s none of my business. The translated names are very similar, which shows that great minds think alike. Good designs always lead to the same result.

No problem!
Gao Zhendong quickly prepared himself mentally and wrote down the words "traveling wave tube" on a piece of paper. He smiled and said, "The traveling wave tube is a new type of signal amplifier device that I just designed. Its basic performance can be summarized in four words: high gain, accurate frequency, high frequency, and wide bandwidth!"

A traveling wave tube is a device that emits a high-energy electron beam into a signal electromagnetic field and transfers energy to the electromagnetic field through the electron beam, thereby amplifying the signal power.

This thing happens to perfectly meet all the requirements of PD radar for power amplifier devices under existing conditions.

Mr. Liu and his entourage, who had no idea that Gao Zhendong had already thought through something, were surprised and delighted when they heard this.

What surprised me was that this Chief Engineer Gao could actually do this? I had never heard of it before.

The good news is, of course, that the new device has promise. Even if you don’t work on PD, this thing can still be very useful.

The greater the gain, the greater the transmission power.

Accurate frequency is of great benefit to signal processing, even when using analog circuits.

A higher frequency means more accurate distance measurement, even when using the pulse time difference method.

High bandwidth is similarly beneficial for accuracy.

As for Gao Zhendong's bragging, it was not within their consideration. What a joke! Would he lie to you?

Even if it takes some time from design to implementation, there will be no problem in principle. Such top experts have to respect themselves. If there are minor problems, they can be corrected. It is better than not seeing the way forward.

If you ask why Mr. Gao hesitated just now, it was probably because of confidentiality, and after careful consideration he decided to reveal a little bit to us.

No wonder they didn't even consider the magnetron issue. This problem doesn't exist there!
This is the highest level of understanding - what is the problem? There is no problem. I don’t know this problem because I have already overcome it.

"Mr. Gao, that's great! Let's put this problem aside for now." Now Chief Engineer Gao was asked to take out this thing called a traveling wave tube. He was worried. Anyway, this project could not be completed in two or three days. It was enough to have the technical source.

(End of this chapter)