Reviewing the development history of base station antenna, every time makes people's blood pound, because it witnesses every leap of mobile communication technology, and also records the youth and memories of generation after generation of communication people.
Over the past few decades, from 1G to 5G, from 2.4Kbps to 10Gbps, the rapid development of mobile communication network behind, inseparable from the base station antenna technology innovation breakthroughs.
The base station antenna is the mobile network's “tentacles”, responsible for sending and receiving wireless signals to the user, and is the mobile network is in the distance near the user's nearest equipment, but also to people in the towns and villages everywhere in the equipment.
Although they are all wrapped tightly in shields and don't look too different, they have changed dramatically over the years ......
1G: Omni-directional antenna
In the 1990s, the price of a “big brother” could easily exceed 10,000 yuan, while people's wages ranged from a few dozen to several hundred. Considering the small number of mobile users and the low call volume of a single station, the operator's network construction principle is to prioritize coverage.
Therefore, 1G base stations use omnidirectional antennas, with a cylindrical or stick antenna to provide 360-degree omnidirectional coverage.
An omnidirectional antenna transmits and receives signals uniformly in all directions, which inevitably brings about the problem of inter-cell frequency interference, but due to the sparse number of stations and the large station spacing at that time, the interference was not too obvious.
It is well known that the coverage shortfall of mobile networks is in the uplink. In the field of mobile communication, we call the signal transmission link from the base station to the cell phone the downlink, and conversely, from the cell phone to the base station, the uplink. Since the transmit power of cell phones is much lower than that of base stations, site coverage is limited by the uplink.
From the 1G era to the early 2G days, to improve the uplink, spatial diversity techniques are usually used, i.e., two spatially separated receiving antennas are deployed on a tower. To ensure isolation, the separation distance between the two antennas is at least 10 wavelengths, e.g., 3.3 m for 900 MHz and 1.67 m for 1800 MHz.
2G: Directional antenna, dual-polarized antenna
Into the 2G era, the introduction of digital technology pushed the cost of equipment down dramatically, and the mobile industry ushered in a golden age of vigorous development. At the same time, antenna technology ushered in unprecedented innovation and development.
The first is sectorization, that is, from omnidirectional antenna development to directional antenna.
With the rapid growth of mobile users, operators' network construction principles began to change from “coverage priority” to “enhance capacity”. One of the techniques to improve capacity is sectorization, i.e., dividing the previous 360-degree omnidirectional coverage into three sectors, each covering 120 degrees.
As a result, the antenna form has evolved from a “stick” to a flat directional antenna, which is encased in a wider housing.
The benefits of directional antennas are not only increased system capacity, but also higher antenna gain due to more concentrated signal radiation, enabling longer coverage distances.
However, since the base station is divided into three sectors, each sector requires the installation of two space diversity unipolarized antennas, which means that the number of antennas on the tower multiplies, not only requiring more sky space, but also increasing the workload of network construction and maintenance.
Perhaps it is for this reason that the base station antenna has seen another major technological advancement - the evolution from a unipolarized antenna to a dual-polarized antenna.
As a kind of inductive device, the antenna will produce electric and magnetic fields, voice and data signals transmitted or received by the electric field. Polarization is the direction of vibration of the antenna's electric field. Radio wave transmissions all operate with some kind of polarization, such as vertical polarization, where the electric field is perpendicular to the ground, and horizontal polarization, where the electric field is parallel to the ground.
Considering that the posture of people talking on the phone is more compatible with vertically polarized signals, early base station antennas generally used single-polarized antennas based on the vertical polarization method.
In contrast, dual-polarized antennas stack two sets of arrays with polarization directions orthogonal to each other (usually +45 degrees and -45 degrees), which can be used to take in two unipolarized antennas in the past in the form of a single antenna's appearance, while ensuring sufficient isolation. In appearance, the biggest difference between dual-polarized and single-polarized antennas is that dual-polarized antennas have two antenna ports corresponding to two antenna arrays of +45-degree and -45-degree polarization.
Dual-polarized antenna breaks the deployment space limitations brought about by spatial diversity, so that the base station antenna can be easily installed on masts, support poles, holding poles, light poles, and other more small footprint communication pole tower facilities, so that the distribution of base stations is becoming more and more dense, and the network coverage is becoming more and more extensive.
3G: Multi-band, multi-beam, remote ESC
The 3G era ushers in the large-scale deployment of dual-band or multi-band antennas.
Each generation of mobile network will allocate new frequency band, antenna as the wireless signal transceiver key device, of course, also need to support the new band. Into the 3G era, in the face of 2.1G and other new frequency bands introduced, operators need to add new antennas to support the new frequency bands on the basis of the original network, once again facing the tower space and load-bearing constraints, the complexity of operation and maintenance issues, at the same time, as some markets have appeared in the tower model, some operators are also faced with the problem of rising tower rental costs.
Therefore, the industry has a strong “single antenna to support dual-band or multi-band” demand, that is, dual-band or multi-band antenna.
In the past, the industry designed one antenna for one frequency band, but now how to realize a single antenna to support multiple frequency bands? There are two ways: one is that the antenna supports a wider frequency range and can cover two or more bands; the other is to integrate an array of radiating elements for different bands into a single antenna housing and ensure that each does not affect the other. Due to the limited frequency bandwidth supported by the radiating elements, the former is only applicable to bands whose frequencies are close to each other; therefore, the latter is more common.
The 3G era also gave birth to remote ESC antenna inclination technology.
Antenna tilt angle, refers to the angle between the main antenna flap and the horizontal plane, it directly affects the network coverage, interference and load balancing, in the mobile network optimization is an extremely important parameter.
There are two ways to adjust the antenna inclination angle: mechanical and ESC. Initially, the mechanical method is used, relying on tower workers to climb up the tower to manually adjust the antenna bracket to tilt the antenna in the desired direction. This approach is obviously very time-consuming and labor-intensive and is not suitable for large-scale network maintenance and optimization.
Compared with manual mechanical adjustment, remote ESC antenna utilizes the signal phase of the oscillator to accurately control the beam tilt, and the operator can adjust the tilt angle by means of remotely controlling the phase shifter inside the antenna. At the same time, for multi-band antennas, ESC antennas can realize independent control of the electrical down tilt angle of each frequency band.
In addition, in the face of 2.5G and 3G introduction of mobile data services, the number of mobile users accelerated growth, the demand for mobile network capacity is further increased, multi-beam antennas came into being.
In the past, an antenna has only one main radiation direction, called single-beam antenna, and one pair of antennas is responsible for the coverage of one sector. Compared to single-beam antennas, multibeam antennas can be assigned multiple beams with main radiation directions, splitting a sector into multiple narrower beams and realizing single-antenna multi-cell splitting.
As a multi-beam antenna has the super ability of “single antenna supporting multiple cells”, the system capacity can be doubled without adding additional antenna equipment, so it is especially suitable for dense urban areas, large-scale activities and other high-capacity hotspot scenarios.
4G: MIMO antennas, multi-port antennas
LTE introduced MIMO technology into cellular networks, so the most beautiful landscape in the 4G era is the MIMO antenna.
MIMO, Multiple-Input Multiple-Output, refers to the deployment of multiple antennas at the transmitter and receiver ends to transmit data streams simultaneously, respectively, to achieve exponential improvement in system capacity and reliability without increasing spectrum resources and transmitter power.
The higher the order of MIMO, the higher the number of antennas, the stronger the system performance. Therefore, we often see 4T4R or even 8T8R antenna configurations in the 4G era. 4T4R means four transceiver antennas are logically configured on the base station side; 8T8R means eight transceiver antennas are logically configured.
Typically, antennas supporting 4T4R have 2 built-in cross-polarization arrays, and 8T8R has 4 cross-polarization arrays. As mentioned above, a dual-polarized antenna comes with two feed ports, and so on, 4T4R with 4 ports and 8T8R with 8 ports.
On one side, it supports high-order MIMO, and on the other side, it faces the coexistence of 2, 3, and 4G multi-standard and multi-band, which requires one physical antenna to support more frequency bands, and thus, the number of antenna ports in the 4G era goes straight up to a new level.
For example, China Mobile's 4G era network has GSM900, FDD900, GSM1800, FDD1800, TD-FA, TD-D multiple bands multiple standards, in order to make a physical antenna to support these bands and to support TD-LTE 8-channel, the industry introduced the 4488 antenna, i.e., 4 ports to support 900M, 4 ports to support 1800M, 8 ports to ports support F&A bands, and 8 ports support D bands.
As each port is connected to the RRU through the feeder line, the multi-port antenna makes the feeder line on the tower more and more dense, and from a distance, it seems as if the antenna has grown a thick black beard.
This obviously does not look very beautiful, but also to the installation and maintenance work more difficult. Perhaps it is out of such considerations, the industry has appeared in the antenna and RRU “combined” program.
This solution not only looks better, is easier to deploy and maintain, but also eliminates feeder losses and saves more power. A further development is the highly integrated active and passive AAU.
5G：Massive MIMO AAU
As you know, one of the most critical technologies for 5G wireless is Massive MIMO. Wireless devices that support Massive MIMO technology are called AAU (Active Antenna Unit).
Massive MIMO AAU has two main features: large antenna array size and many RF channels. For example, a typical AAU supporting 3.5GHz 64T64R has 192 antenna units and supports 64 transceiver channels.
This brings two technical advantages: first, in the face of 5G higher frequency, signal coverage ability is weaker, Massive MIMO can adjust the amplitude and phase of multiple antenna units to achieve beam fouling, so that the wireless signal energy is more concentrated, pointing more accurately, so as to enhance the coverage ability and reduce the signal interference; second, it is possible to concurrently serve multiple users through multiple data streams, to enhance the system capacity.
Massive MIMO strongly support the development of 5G, the future of this technology will be “super large-scale MIMO”, “very large-scale MIMO” continued to evolve. In the face of the 6G era or the introduction of 7GHz and other higher frequency bands, the AAU will be upgraded from 64TRx to 128TRx, 256TRx or even 512TRx, and the number of antenna units will be upgraded from 192 to hundreds or even more than a thousand.
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