Chapter 891 Multi-Band Phased Array Antenna

“From the perspective of signal processing algorithms, this is indeed the case.”

Chang Haonan took two steps back, stared at the blackboard for a few seconds, and then answered:

"But shouldn't we have known this before...?"

Wang Xiaomo's question was a little beyond Chang Haonan's expectations.

Because he had not expected that the other party or other researchers in the field of radar engineering would focus on this.

"Before?"

Wang Xiaomo turned his head and looked at the blackboards he had just talked about, with some confusion in his tone:

"But you haven't written anything related to this model expression before?"

"No...I'm not talking about before this."

Chang Haonan waved his hand:

"I mean... before today."

“Isn’t it a consensus that the mathematical model of an optically controlled linear phased array…or any linear phased array, includes three vectors?”

This question has not been responded to.

But it is not difficult to see the answer from Wang Xiaomo's eyes——

"Could it be?"

"hiss……"

Chang Haonan originally thought that he had simply derived a model expression when the independent variables were known.

The result is that a towering building rises from the ground...

If it were in the field of theoretical mathematics, then in order to get the complete process, he would have to first prove that "the model only contains three vectors".

Fortunately, the engineering field doesn’t care much about these details, as long as they can match the actual situation, there is no big problem.

So, after this brief episode, Chang Haonan's introduction went on smoothly.

However, the following content is much more logical in comparison...

"The pulse signal sent by the radar system will be affected by factors such as target scattering and propagation path during the propagation process, resulting in the broadening of the time and frequency domains of the echo signal. Therefore, in order to improve the resolution, the echo signal needs to be pulse compressed. This process is usually completed in the time or frequency domain using matched filtering or related signal processing..."

He talked as he walked, and occasionally added some additional content on the blackboard.

Finally, after more than an hour, he came to the last blackboard.

At this time, Wang Xiaomo's pen had already stopped.

Compared with the previous part, although the latter half is larger in terms of pure computational complexity, it is much easier to understand because it does not have such exaggerated jumps.

This also gave him more time to think about some issues in the field of radar engineering.

"..."

“……通过卷积由式上式可以求出阵列的脉冲压缩输出结果：s(t)在匹配匹配滤波器后输出为s‘(t)=∑(n=1，N)e^(jφ){e^[j2π(f(t-(t0-t))+u(t-(t0-t))T)-e^(j2πf(t-(t0-t)))]}……”

Chang Haonan pointed to the lower right corner of the blackboard, the end of all the equations.

Then he turned around, took two steps forward, and sat back at the conference table.

Then he opened the laptop that had been on the table from the beginning but had never been turned on:

"Based on this model, I conducted numerical simulations on pulse compression of optically controlled phased arrays and fully phase-shifted phased arrays in a typical case."

He turned the computer 180 degrees and pushed it in front of Wang Xiaomo:

"From these two result graphs, we can see that the maximum pulse pressure of the full phase-shifted phased array is 4.21dB lower than the maximum pulse pressure of the optically controlled delay array, which means that the signal-to-noise ratio is lost by 4.21dB."

“另外，子阵延时光控阵列的脉压的4dB宽度为5.12ns，旁瓣高度为-13.84dB，峰值时间位置为49.9989ms；而全移相阵列的脉压4dB宽度为7.088ns，旁瓣高度为-26.32dB峰值时间位置为49.9952ms。”

"Therefore, the main lobe of the LFM signal in the full phase-shift array is widened after pulse compression, the peak time position deviates greatly, and a certain signal-to-noise ratio is lost. In addition, the spectrum structure of the broadband LFM signal of the full phase-shift phased array is no longer a rectangular distribution, which will result in the resolution after pulse compression being lower than expected."

Staring at the normalized amplitude-time curve on the computer screen, Wang Xiaomo did not speak immediately.

There is no doubt that, judging from the results obtained by Chang Haonan, the optically controlled phased array has advantages in mechanism that traditional phased array radars cannot achieve.

Especially in the field of wide-angle scanning, which he had previously paid great attention to.

While waiting for the computer to start up and open the document for a few minutes, Wang Xiaomo had already roughly calculated several results on his notebook.

Conservatively estimated, thanks to the broadband characteristics and low loss of fiber TTD, the available scanning angle of the single-sided optically controlled phased array will be able to be expanded to ±75° or even ±80°.

This is a huge improvement for fixed single-sided or double-sided array antennas.

but……

Not big enough.

Almost at the same time as he saw the simulation results on the computer, he came up with a more radical idea.

"Mr. Chang."

Wang Xiaomo put the ballpoint pen aside:

“What if we don’t pursue expanding the scanning angle?”

"what?"

Chang Haonan was stunned by this question.

You said before that you wanted wide-angle scanning, and I calculated the result for you, but now you don’t need it?

What's going on?

Seeing his surprised expression, Wang Xiaomo quickly continued to explain:

"What I mean is, since scanning angle and instantaneous bandwidth are a pair of contradictory indicators, and since optically controlled phased array radar can achieve a large scanning angle under the same bandwidth, can we also change the idea and achieve a high bandwidth under the same scanning angle?"

After hearing this idea, Chang Haonan lowered his head and thought.

Then he frowned slightly.

Then his eyes lit up.

"It should be... yes!"

After all, he was not a radar professional, and the calculations he had just made were only theoretical deductions from the mathematical and physical levels, so his ideas on the application level were actually a bit limited.

When he was in Nanzheng before, Wang Xiaomo had been talking about the problem of wide-angle scanning, so his calculation results have been moving in this direction.

But now that he was reminded by the other party, his thoughts were immediately opened up -

The bandwidth of radar is not the same as the bandwidth of network.

It is not a unit of speed, but a unit of frequency.

Refers to the frequency bandwidth that the radar antenna can adapt to under normal working conditions.

We often say that a radar "operates in a certain band".

This band range is the bandwidth.

In most cases, the radar's back-end module does not care about the frequency band.

But the adaptability of the transmitting/receiving antenna is very poor.

So overall it will show narrowband characteristics.

However, as Wang Xiaomo just said, optically controlled antennas can completely overcome this problem.

The demand for wide-angle scanning for China's future main equipment, whether it is the rotatable double-sided/single-sided array of early warning aircraft or ground-to-air missile system, or the four-sided array to be used on warships, can be summarized as "it's best to have, but it's okay without."

But broadband is another matter.

To exaggerate a bit, it is even possible to achieve dual-band or even multi-band detection through the same array!

"If the scanning angle remains unchanged at 120° or 90°."

Thinking of this, Chang Haonan pulled the computer back in front of him and began typing on the keyboard rapidly.

The complex simulation process just now was naturally completed on a supercomputer, and here only a screenshot of the result is shown.

But if we just convert the bandwidth and scanning angle, the performance of the PC is still sufficient.

Time passed minute by minute, and Wang Xiaomo, who was sitting opposite, finally lost his patience and walked around the desk to behind Chang Haonan, hoping to see the result as soon as the calculation was completed.

Chang Haonan input a series of calculation commands, but the calculation process itself did not last too long.

The results quickly appeared on the computer screen.

"Well... broadband performance in different bands is actually somewhat different."

Chang Haonan read it quickly and then concluded:

"Generally speaking, for the S-band and adjacent frequency bands commonly used by search radars, if the search range is controlled at ±60°, the frequency range can cover about 2.7Ghz, which is basically a complete frequency band plus a less complete frequency band."

"If the range is adjusted to ±45°, the frequency range can cover up to 3.7Ghz, which is two complete frequency bands, or one complete band plus two less complete bands..."

"For higher frequency ranges, the available bandwidth will be slightly reduced accordingly. For example, for the X-band commonly used by fire control radars, even if the scanning range is controlled at ±45°, it can only cover 2.9Ghz..."

Wang Xiaomo clenched his right fist and tapped his chest lightly.

Obviously, this result was a bit too surprising for the old comrades.

After a short pause, he spoke:

"It doesn't matter. Fire control radar has higher requirements for resolution. Pursuing a large bandwidth is probably not as meaningful as a large scanning angle. Let's focus on the search radar."

"For example, the sea-based 346 radar, which is almost finished testing, operates in the S band, but the guidance and command system of the HQ-9 air defense missile operates in the C band. We originally planned to install an additional set of transceiver antennas under the main radar array, but if the radar can operate in both the S and C bands at the same time, we can save this trouble..."

Chang Haonan thinks more long-term:

"The shipborne four-sided array only needs a ±45° operating range, so the radar can even work in the L, S and C bands at the same time, such as 1Ghz to 4.7Ghz. In this way, the 346 radar can even directly replace the 517A radar to obtain a certain anti-stealth and ultra-long-range detection capabilities..."

517A is the model with the clothes-drying-rack-shaped antenna at the rear of the 052C/D destroyer. It is an old predecessor that has been in service from the 50s to the 21st century.

Although the overall performance is somewhat behind, due to the nature of the P band, it still has certain anti-stealth and long-range surveillance potential.

This is something that a simple S-band radar cannot match in principle.

Therefore, until the later 052D and even 055, they were modified again and again and continued to be used.

But if the 346 radar itself can operate in the L band, which has similar properties to the P band, the demand for 517A will be greatly reduced.

Wang Xiaomo and Chang Haonan looked at each other and almost simultaneously saw the huge potential of this technology in each other's eyes.