Chapter 270 Passive Radar Detection

Although Chang Haonan had reduced the length of the telegram as much as possible, he still ended up writing about two to three thousand words.

And almost every sentence must be carefully considered.

After all, many of the details come from memories of previous lives, so there is definitely no way to write them down directly.

In order to increase his persuasiveness, he had to say that the maximum takeoff weight of the An-70 is only three-quarters of the IL-76MF, making it an easier reference in the future.

Fortunately, the core of this proposal, namely Antonov's lack of money, is easy to explain.

Just say it was a guess.

Everyone can guess it anyway.

It's just that Chang Haonan knew very clearly how short of money they were, so he dared to make such a bold plan.

After this operation was completed, the telegram was handed over to the director of the confidential office who had been waiting outside. The entire afternoon had passed, and it happened to be dinner time.

Standing in the cool breeze of early April, the tiredness caused by being bored in the confidential room for an afternoon disappeared in an instant.

Chang Haonan remembered that a few hours ago, he decided to have a good meal.

After hesitating for a moment, I felt that it was a bit outrageous to eat alone.

After receiving many high bonuses (by the standards of this era), and not having to spend any money on food and drink, he can now be considered a wealthy man.

Finally, he changed direction and prepared to go back and call in the comrades from the 14th Institute who came to Yan Liang on a business trip, and of course Xu Yang.

As for the name, it is just to boost morale and prepare for the next round of electronic warfare pod testing. Anyway, if we count the days, Jinling should also be shipping things over.

But when he pushed open the door of the research room, he found that everyone inside was already beaming with joy, as if they knew in advance that someone was going to treat them tonight.

"Everyone, how about we go out for dinner tonight?"

Although he was a little curious, Chang Haonan, who was in a good mood, decided to talk about the important things first.

Then he received a dozen looks with the same confusion and surprise:

"Chang Gong, didn't you go out in the afternoon?"

"Yes."

Chang Haonan nodded.

"Then how do you know that Guo Gong has come up with a good idea?"

"Yes, Dr. Xu also thinks his idea is fine."

"And we simulated it on the previous circuit, and it completely works."

"..."

Everyone was talking to each other, and Chang Haonan finally understood that this was probably a mistake.

"So, what's the idea?"

He took off the scarf around his neck and hung it next to him, walked to Guo Lin and asked.

Lin Shikuan of Institute 601 had already become an independent digital design engineer under the guidance of him and Yao Mengna, and solved many problems for the aviation industry when Chang Haonan was unable to do anything else.

It would be nice if it could be reproduced in the 14th Institute of Electrical Engineering.

"Cough-cough-"

Hearing Chang Haonan's question, Guo Lin instantly became excited.

After so long, it’s finally my turn to show off.

He instantly switched to sitting upright.

Unfortunately, there was no one with enough eyesight to hand over a pen and paper, so he had to take it from the table next to him, which reduced the B level of this set of actions a lot.

"I thought of a way to specifically confirm the enemy's location by detecting the radar signals emitted by the enemy."

"Specific location? Including distance?"

Chang Haonan instantly became interested.

The technology of passive tracking of radar radiation sources has been used in Suppressed Air Defense Operations (SEAD) since the Vietnam War. However, in fact, until the mid-90s, this detection could only obtain the target's orientation information, but could not Directly determine the distance between ourselves and the enemy.

Of course, for general anti-radiation missiles and electronic interference, this is not a problem, because even if I don’t know the target distance, as long as I always follow the direction of the radar wave, I can always find the signal source.

However, with the continuous advancement of air defense technology, the signal detectability of the radar itself is constantly decreasing, and the radar emission source can even work while moving at high speed. This results in the traditional single-station passive positioning being unable to continuously and stably track the signal emitted by the radiation source. As a result, a huge registration deviation occurred, and the efficiency of hard-killing radars through the combination of passive detection and anti-radiation missiles declined sharply in the 90s.

For example, the AGM88 Hamm could kill almost indiscriminately in 1982, but in 1999, facing the southern army with weaker resistance, the hit rate dropped to a horrific level.

This situation has also given rise to the third generation of electronic warfare aircraft represented by EA18G.

Now Guo Lin said that he could solve this problem, which really shocked Chang Haonan.

"Uh... that's not possible."

Guo Lin scratched his head in embarrassment:

"But radar signals can be sorted in complex electromagnetic environments and the most threatening one can be effectively identified. This is at least much better than our current method, which can only intermittently obtain target signals."

"Oh……"

This answer slightly dampened Chang Haonan's newly heightened thirst for knowledge.

But it’s okay, at least it’s an improvement:

"tell me the story."

"That's right. A few years ago, someone proposed a transformation algorithm based on harmonic suppression of the autocorrelation function, which can transform the pulse signal TOA from the time domain to the PRI domain, effectively suppressing the harmonics of the real PRI of the pulse signal. , that is, if we assume that the TOA of each pulse is the ideal unit shock function δ..."

"Wait a minute."

Chang Haonan directly stopped Guo Lin's introduction:

"I know the PRI, we can just go to the next section."

"Uh...ok."

Guo Lin next to him also realized that he was a little carried away and tried to introduce this basic knowledge to the other party, so he quickly collected his thoughts and continued:

"In short, as the pulse TOA of the jittered PRI signal increases, the PRI algorithm's error in the pulse phase factor will continue to increase. In addition, the accumulated pulses of the jittered signal will be dispersed into different PRI boxes."

"So I thought that this algorithm can be improved in two ways. One is to introduce the concept of a variable time starting point to avoid errors caused by phase factors, and the other is to use overlapping PRI boxes for anti-shake processing... In short , the process I designed is roughly like this.”

He was obviously prepared and took out a beautifully drawn flow chart directly from underneath and handed it to Chang Haonan.

At this time, the latter had forgotten what he had just thought about going to eat on the way. He picked up the piece of paper and lowered his head to think.

After watching motionless for more than ten minutes, Chang Haonan finally raised his head again and looked at Guo Lin next to him:

"The idea is very complete. It's pretty good for a person to think of this."

"I'm not the only one. Other comrades have also helped me correct some things these days. Fortunately, judging from the test results, the repeated frequencies of the three groups of signals can be identified simultaneously through an improved PRI transformation calculation, and There are no false PRI peaks, and the processing capabilities for strong jitter signals have been greatly improved."

Guo Lin was a little embarrassed and smoothed his hair.

He intentionally did not consult Xu Yang and Chang Haonan before this afternoon, just to see if he could figure this idea out at his own level.

"Good idea."

"However, just to identify the target signal, we can still only use electronic interference for soft kill, which may not be enough in the operations facing the new century."

"I have a straightforward personality and like to cut grass and roots. If I don't blow up the enemy's radar, it's always a hidden danger."

Chang Haonan put down the paper in his hand:

"But having said that, your idea inspired me."

"On the basis of being able to effectively sort radar signals in complex environments, there is no need for us to focus on anti-radiation operations... It should be possible to use some means to allow aircraft to use passive radar to directly detect and track targets. Ability, I mean, even if the target does not have the radar turned on, of course it would be better if it is the target with the radar turned on."

"Ah this?"

Guo Lin's expression became a little stiff.

Chang Haonan also noticed that the other party seemed to be a little bit shocked:

"However, your algorithm still has academic value. If it is published, it may be difficult to publish it in professional control journals, but there is still hope for journals that intersect aerospace and control disciplines, such as IEEE Transactions on Aerospace and Electronic Systems. .”

"Is it really okay to publish this...?"

As an employee of Institute 14, I still have this sensitivity.

"No problem. The PRI algorithm itself is not a new thing, and it is quite basic research. Rather than holding it in your own hands, it is better to publish it so that more people can see it."

"The key to implementing it into a specific model is this part that I just thought of."

"..."

This time Guo Lin was hit even harder.