Large scale integrated phased array solves the problem of short millimeter wave propagation distance

Because of its rich bandwidth resources, millimeter wave band is gradually becoming the "golden band" for the development of broadband satellite communications, 5g and even the future 6G mobile communications. However, the short wireless transmission distance of millimeter wave restricts its application. The integrated phased array is one of the key technologies to solve the limited propagation distance of millimeter wave wireless communication.
The traditional millimeter wave phased array is usually implemented based on compound semiconductor chip. Due to the high production cost, its application range is greatly limited. In the past six years, you Xiaohu, Zhao Dizhen and other scholars from the State Key Laboratory of mobile communication of Southeast University, together with Zijinshan Laboratory of network communication and security and Tianrui Xingtong Technology Co., Ltd., have continued to tackle key problems, breaking through the inherent bottle neck of complementary metal oxide semiconductor (CMOS) devices, successfully developed Ka band millimeter wave CMOS phased array chips, and explored high-density hybrid PC B-PROCESS large-scale integrated phased array solution has the characteristics of ultra-high integration and ultra-low cost.
Recently, the "top ten scientific and technological progress of Chinese colleges and universities" in 2020 was announced, and the research project of "CMOS millimeter wave chip and large scale integrated phased array" was selected.
Extending millimeter wave transmission distance with phased array
Millimeter wave generally refers to the radio spectrum in the range of 30ghz to 300GHZ. Compared with the traditional mobile communication radio spectrum, the frequency is much higher. The wavelength of millimeter wave ranges from 1 mm to 10 mm, which is the origin of the name "millimeter wave".
"The bandwidth of millimeter wave is very wide, which is equivalent to widening the lanes of expressways several times, so it can carry more information transmission. However, a major bottleneck of millimeter wave is its short wavelength, which is easier to be absorbed by the atmosphere and water, and also easily blocked by buildings, so the propagation distance is short. Whether this problem can be solved is one of the key points to determine whether millimeter wave can be used in 5g and satellite communication You Xiaohu said that in order to solve this problem, the scientific research team tackled difficulties from two technical directions.
Large scale phased array is the key technology to solve the problem of limited propagation distance of millimeter wave. Phased array is an electromagnetic wave receiving and transmitting system. The higher the frequency and shorter the wavelength of electromagnetic wave, the smaller the antenna unit is, and it can accommodate more antennas in the same area. More than one antenna, densely arranged into a square array, constitutes the antenna array.
You Xiaohu explained: "generally speaking, radio waves propagate in a spherical shape, so the signal transmission energy is relatively scattered. The use of phased array can make the signal propagate along a certain direction and concentrate the energy in a relatively unified direction, so as to extend the propagation distance. Just like a flashlight, it aims at the target and covers accurately. The transmission distance can be extended from several meters, tens of meters to 30000 kilometers or even farther, which can be used for mobile communication and satellite mobile communication with longer distance. "
At the same time, the scientific research team is also trying to solve the problem of signal radiation shielding, "for example, multiple distributed millimeter wave phased array base station front ends can be deployed, so that at least one millimeter wave base station front end can be connected with the user's mobile phone at any location, which not only solves the problem of transmission distance, but also solves the problem of signal shielding, and can realize large traffic transmission at the same time." You Xiaohu said.
Ingenious design to solve CMOS process problems
There are many semiconductor production processes, including SiGe process, compound semiconductor process and CMOS process. You Xiaohu said that in the early development of the industry, phased arrays were made of compound semiconductor materials, but in the past five years, the industry has begun to focus on millimeter wave integrated circuits based on CMOS technology. CMOS technology is the most widely used technology in the industry. Most mobile phones and electronic products are processed based on CMOS technology, which is also the easiest process to achieve low cost, high integration and large-scale mass production.
"However, when the signal transmission frequency is relatively high, this process mode will have some negative characteristics, such as sensitivity to temperature, relatively high noise figure, and it is difficult to raise the transmission power to a very high level. How to solve these problems through ingenious design is not a small challenge. " You Xiaohu gave an example. The research team designed a series of circuits with new architecture, which skillfully used the inherent characteristics of each electrode of CMOS transistor to reduce power consumption and improve gain without introducing additional noise, thus solving these technical problems.
In addition, the R & D team has formed a phased array system with stable performance by using high-density hybrid multilayer circuit board technology, overcoming the technical consistency problem faced by mass production of millimeter wave phased array. In order to realize large-scale batch manufacturing, process state stable control, automatic monitoring and inspection, product yield improvement, and provide guarantee for large-scale batch production of phased array products, the R & D team proposed standardized splicing technology to flexibly splice small-scale phased array subarrays into large-scale phased array required by users.
Finally, after six years of technical exploration and innovation, the project team successfully developed 4096 channel transceiver integrated phased array, which is the most integrated and largest CMOS millimeter wave integrated phased array in the world, and its key technical indicators such as equivalent omnidirectional radiation power are far ahead of similar international research. At the same time, the noise figure of the chip is only 3dB, and the efficiency of the transmitting channel is up to 15%.
The results have been applied in a large scale
CMOS millimeter wave chips and large-scale integrated phased array, which are becoming more and more mature, have gone out of the laboratory and are gradually realizing industrialization. You Xiaohu said that at present, CMOS millimeter wave chips and large-scale integrated phased array have been widely used in large-scale applications. More than 30 manufacturers are developing their own products around this technology, and the results have been widely used in vehicle, ship and UAV broadband satellite mobile communication and millimeter wave 5g fields.
"Now the millimeter wave terminal can be installed in cars, ships and UAVs to realize communication with satellites. If you drive to a very remote area where there is no mobile communication signal, you can receive satellite signals through the vehicle mounted millimeter wave terminal, and then convert the received signals into WiFi." You Xiaohu imagined that in the future, this technology can be directly applied to mobile phones to interconnect with LEO satellites. When there is a signal in the ground mobile communication system, the mobile phone can receive the ground signal, and when the ground signal is weak, the mobile phone can automatically receive the satellite signal, ensuring the stable and smooth connection of mobile communication anytime and anywhere. However, he said frankly that it may take 5-10 years or more to realize this vision.