In the past two decades, the key technologies of communication have changed, and we have witnessed the transformation of mobile communication from 1G to 4G LTE. During this period, the key technologies of communication are changing, and the amount of information processed is doubling. The antenna is an indispensable component to achieve this leapfrog promotion.
Antenna, the electromagnetic wave that is propagating, or the opposite transformation, that is, transmitting or receiving electromagnetic waves. Simply say, whether it is a base station antenna or a mobile terminal, the antenna acts as middleware for transmitting signals and receiving signals.
The fifth-generation communication technology—5G has entered the standard-setting stage, and major operators are actively deploying 5G equipment. Undoubtedly, 5G will bring a new experience to users, it has a transmission rate ten times faster than 4G, and puts new requirements on the antenna system. In 5G communication, the key to achieving high speed is millimeter wave and beam-forming technology, but the traditional antenna obviously cannot meet this demand.
The first generation of mobile communications used almost all omni directional antennas. At that time, the number of users was small and the transmission rate was low. At this time, it was also an analog system.
The second generation of mobile communication technology, we entered the cellular era. The antenna at this stage has gradually evolved into a directional antenna, and the general lobe width includes 60° and 90° and 120°. Taking 120° as an example, it has three sectors.
The antennas of the 1980s were mainly dominated by single-polarized antennas, and the concept of arrays has begun to be introduced. Although omni directional antennas also have arrays, they are only vertical arrays, and single-polarized antennas have planar and directional antennas. In terms of form, the current antenna is very similar to the second generation antenna.
In 1997, dual-polarized antennas (±45° cross-multi-polarized antennas) began to enter the historical arena. At this time, the performance of the antenna has been greatly improved compared with the previous generation. Whether it is 3G or 4G, the main trend is a dual-polarized antenna. In the 2.5G and 3G era, many multi-band antennas appeared. Because the system at this time is very complicated, such as GSM, CDMA, etc. need to coexist, multi-band antenna is an inevitable trend. In order to reduce costs and space, multi-band has become the mainstream at this stage. By 2013, we introduced the MIMO (Multiple-Input Multiple-Output) antenna system for the first time. Originally a 4x4 MIMO antenna. MIMO technology has increased communication capacity, and the antenna system has entered a new era, from the original single antenna to the array antenna and multiple antennas.
However, now we need to look into the distance, 5G deployment has started, what role will antenna technology play in 5G, and what impact will 5G have on antenna design? This is the problem we need to explore.
In the past, the design of the antenna was usually very passive: after the system design was completed, the indicator was added to customize the antenna. However, the current concept of 5G is still unclear. R&D personnel who do antenna design need to be prepared in advance to provide solutions for 5G communication systems, and even influence the customization and development of 5G standards through new antenna solutions or technologies.
From the experience of cooperation and exchange between mobile communication companies in the past few years, there are two major trends in base station antennas in the future.
First, from passive antennas to active antenna systems.
This means that the antenna may be intelligent, miniaturized (co-designed), and customized.
Because the future of the network will become more and more detailed, we need to customize the design according to the surrounding scenes, for example, the station in the urban area will be more elaborate, rather than simple coverage. 5G communication will use high-frequency bands, obstacles will have a great impact on communication, and customized antennas can provide better network quality.
Second, the trend is a systematic and complex antenna design.
Such as beam array (implementation of space division multiplexing), multi-beam shaped stadium antennas and multi/high-frequency bands. These all place high demands on the antenna, which will involve the entire system and compatibility issues. In this case, the antenna technology has surpassed the concept of components and gradually entered the design of the system. The evolution of antenna technology: from the single array of antennas to multiple arrays to multiple units, from passive to active systems, from simple MIMO to massive MIMO systems, from simply fixed beams to multiple beams. For base stations, a major principle of antenna design is miniaturization. The antennas of different systems are designed together. In order to reduce the cost and save space, the antennas are small enough. Therefore, the antennas need multi-band, wide-band, multi-beam, MIMO/Massive MIMO, and MIMO isolation. Massive MIMO antenna has some special requirements for the hybrid coupling of antennas. In addition, the antenna also needs to be tunable. The first generation of antennas was mechanically used to achieve tilt angles, and the third generation achieved remote ESCs. 5G is very attractive if it can achieve self-tuning.
For mobile terminals, the requirements for the antenna are also miniaturized, multi-band, wide-band, and tunable. Although these features are now available, the 5G requirements will be more demanding. In addition, the antenna of 5G mobile communication faces a new problem - coexistence. To implement Massive MIMO, multiple antennas are required for transmission and reception, that is, multi-antenna (8-antenna, 16-antenna...). The biggest challenge for such a multi-antenna system to the terminal is coexistence. How to reduce the mutual influence to the couple, how to increase the isolation of the channel... This puts new requirements on the 5G terminal antenna.
Specifically, it will cover the following three points:
Reducing the mutual influence, especially the different functional modules, the mutual interference between different frequency bands, which was not considered by the academic community before, but this problem does exist in the industry; decoupling, in the MIMO system, the mutual antenna Coupling not only reduces the isolation of the channel but also reduces the radiation efficiency of the entire system. In addition, we can't expect to rely entirely on high-band millimeter-waves to address performance gains, such as 25GHz, 28GHz...60GHz, all with system problems;
De-correlation, which can be solved by an antenna and circuit design cooperation, but the bandwidth of the solution is very limited by the circuit, and it is difficult to meet the bandwidth of all frequency bands.
Antenna technology for 5G systems
This includes the design of a single antenna and the technology at the system level, as mentioned above at the system level, such as multi-beam, beam-forming, active antenna array, Massive MIMO, etc.
First, the antenna design, the technology developed based on the concept of super material will be of great benefit. Metamaterials have been successful in 3G and 4G, such as miniaturization, low profile, high gain and band.
Second, the substrate or package integrated antenna. These antennas are mainly used in the frequency band with high frequency, that is, the millimeter wave band. Although the antenna size in the high-frequency band is small, the loss of the antenna itself is very large, so it is preferable to integrate the antenna and the substrate integration or a smaller package on the terminal.
Third, the electromagnetic lens. The lens is mainly used in high-frequency bands. When the wavelength is very small, a medium can be used to go to the focus. The high-frequency antenna is not large, but the wavelength of the microwave segment is very long, which makes the lens difficult to use. It will be great.
Fourth, the application of MEMS. At very low frequencies, MEMS can be used as a switch. In mobile terminals, if the antenna can be effectively controlled and reconstructed, an antenna can be used. Taking an electromagnetic lens as an example, this design introduces a concept: an electromagnetic lens is placed in front of a multi-unit antenna array (here, a lens applied to the low-end frequency band of microwave or millimeter wave, unlike a conventional optical lens), when light When incident from an angle, spots are generated on a focal plane, which concentrates a large amount of power, which means that the main part of the entire capability is received in a small area.
When the incident direction changes, the position of the spot on the focal plane also changes. The direction of incidence and the position of the energy on the array or on the focal plane are in one-to-one correspondence. Conversely, if the antenna is excited at different positions, the antenna will radiate in different directions, which is also one-to-one correspondence. If multiple cells are radiated on the focal plane, radiation of multiple carrier beams can be generated, which is called beam-forming; if switching between these beams, beam scanning occurs; if these antennas are used simultaneously, Massive MIMO can be implemented. This array can be large, but high gain radiation can be achieved with very few arrays per beam.
Ordinary arrays, if they have the same size, each time the energy is received, all the cells must receive energy in this area. If only one unit is placed in a large area, the energy received is only a very small part; The difference in the array is that the same caliber can receive all the energy with only a few units without any loss. Different angles come in, and these energies can be received simultaneously in different places.
This greatly simplifies the entire system. If there is only one direction per work, only one local antenna can work, which reduces the number of simultaneous working antennas. The concept of sub-array is different. It is to make the local multi-antenna form a sub-array. At this time, the number of channels is reduced as the number of sub-array units increases. For example, a 10×10 array, if it becomes a sub-array with 5×5, then it becomes only four independent channels, and the total number of channels is reduced, the complexity is reduced, the coverage efficiency is increased, and the antenna can be added. The filtering characteristics of the array (shielded interference signals) and so on.
In the future, the antenna must be designed together with the system instead of being designed separately. It can even be said that the antenna will become a bottleneck of 5G. If the bottleneck is not broken, the signal processing on the system cannot be realized, So the antenna has become the key technology of 5G mobile communication system. An antenna is not just a radiator. It has filtering characteristics, amplification, and suppression of interference signals. It does not require energy to achieve gain, so the antenna is more than just a device.
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