Over the past two decades, we have witnessed the shift in mobile communications from 1G to 4G LTE. During this period, the key technologies of communication are changing, and the amount of information processed has multiplied. The antenna is an indispensable component to achieve this leapfrog.

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What is the future antenna technology of 2G to 5G?
Over the past two decades, we have witnessed the shift in mobile communications from 1G to 4G
LTE. During this period, the key technologies of communication are changing, and the amount of
information processed has multiplied. The antenna is an indispensable component to achieve this
leapfrog.
According to the industry definition, an antenna is a transducer that transforms a guided wave
propagating on a transmission line into an electromagnetic wave propagating in an unbounded
medium (usually free space), or vice versa, that is, transmitting or receiving electromagnetic
waves. Popularly speaking, whether it is a base station or a mobile terminal, the antenna acts as
a middleware for transmitting signals and receiving signals.
Now, the next-generation communication technology, 5G, has entered the end of the
standard-setting phase, and major operators are actively deploying 5G devices. 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 beamforming technology, but the traditional antenna obviously cannot
meet this demand.
Circuit characteristics and radiation characteristics are important indicators of base station
antennas, such as gain, lobe width, front-to-back ratio, standing wave ratio, isolation, third-order
intermodulation, and so on. As the antenna age increases and the intermittent high power input,
the RF path temperature rises rapidly, accelerating the aging of the material, causing the
attenuation of its radiation characteristics to affect the entire base station system.
What kind of antenna does 5G communication need? This is a problem that engineering
developers need to think about.
A new round of technology and industrial transformation, represented by information technology,
is gradually gestating and upgrading. With the proliferation of video traffic, the growth of user
equipment and the popularity of new applications, there is an urgent need for the rapid maturity
and application of the fifth-generation mobile communication system (5G), including mobile
communications, Wi-Fi, high-speed wireless data transmission, without exception. The need for
faster transfer rates, lower transfer latency, and higher reliability. In order to meet the high data

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rate requirements of mobile communications, one needs to introduce new technologies to
improve spectrum efficiency and energy utilization efficiency, and the second is to expand new
spectrum resources.
Broadband antenna miniaturization
Passive antenna activation
Fixed antenna reconfigurable
HF antenna integration
Military antenna civilization
Two new types of antenna technologies, including tightly coupled terminal antennas based on
coupled resonator decoupling networks; MIMO based on metamaterials (super-surface), Massive
MIMO antenna array coupling reduction and performance improvement techniques. Through the
testing and evaluation of passive parameters, active parameters, and MIMO parameters, the
obvious advantages and broad application scenarios of these two new types of antennas in 5G
are confirmed.
In this context, large-scale multi-input and multi-output technology (Massive MIMO) has become
an irreversible core technology for improving spectrum efficiency in the next generation of
mobile communication systems. Multiple Input-Output Technology (MIMO) can effectively utilize
multiple spatial channels existing between multiple antennas between transceiver systems to
transmit multiple mutually orthogonal data streams, thereby improving data throughput without
increasing the communication bandwidth. Rate and stability of communication. Massive MIMO
technology goes one step further on this basis. Based on limited time and frequency resources,
hundreds of antenna units are used to serve up to dozens of mobile terminals simultaneously,
which further improves data throughput and energy usage. effectiveness
Evolution and trend of mobile communication base station antenna
The base station antenna is developed along with network communication, and engineers design
different antennas according to network requirements. Therefore, in the past few generations of
mobile communication technologies, antenna technology has also been evolving.
The first generation of mobile communications used almost all omnidirectional 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.
By 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 omnidirectional 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 dual-polarized
antenna.
In the 2.5G and 3G eras, multi-band antennas have emerged. Because the system at this time is

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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, the deployment of 5G has started, what role
does antenna technology play in 5G, and what effect will 5G have on antenna design? This is a
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 another perspective, array antennas, multi-band antennas, and multi-beam antennas
constitute the "magic triangle" for the development of base station antennas.
Massive MIMO
The base station is equipped with a large-scale antenna array, which utilizes spatial freedom
formed by multiple antennas and effective multipath components to improve the spectrum
utilization efficiency of the system.
Multi-beam antenna
Multi-beam antennas use multiple beams to split the sector, increasing capacity.
2G to 4G base station antenna development
In the 2G/3G era, the antenna is mostly 2 ports.
▲GSM antenna
▲CDMA antenna
▲ LTE-FDD independent 2-port antenna (2T2R)
In the 4G era, with the massive use of MIMO technology and multi-band antennas, we saw that
the antenna on the tower is like a big beard.
▲ LTE-FDD independent 4-port antenna (2T4R)
▲CDMA (1T2R)/LTE-FDD (2T4R) 6-port dual-band antenna
▲LTE-TDD 8T8R 8-port antenna
Together with the RRU on the tower, the scene on the tower is quite spectacular...
What might the future base station antenna look like?
With the evolution of the C-RAN network structure, the RRU is far away, and various hidden
antennas will appear...
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.
The first is 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

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coverage. 5G communication will use high-frequency bands, obstacles will have a great impact on
communication, and customized antennas can provide better network quality.
The second trend is the systematic and complex antenna design.
For example, beam array (implementing space division multiplexing), multi-beam 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 simple fixed beams to multiple beams.
Design level trend
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 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 frequency
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:
1. 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;
2. Decoupling, in MIMO systems, the mutual coupling of the antenna 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;
3. De-correlation, which can be solved by the antenna and circuit design coordination, but the
solution bandwidth is very limited through the circuit, 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, beamforming, active antenna array, Massive

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MIMO, etc.
From the perspective of specific antenna design, the technology developed by the
metamaterial-based concept will be of great benefit. Metamaterials have been successful in 3G
and 4G, such as miniaturization, low profile, high gain, and band.
The second is 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.
The third is an 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.
The fourth is 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.
If multiple cells are radiated on the focal plane, radiation of multiple carrier beams can be
generated, which is called beamforming; 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 this energy 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
the subarray 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.
Millimeter wave antenna design
Another key technology of 5G is the high-frequency band (millimeter wave) transmission.
Traditional mobile communication systems, including 3G and 4G mobile communication systems,
whose operating frequencies are mainly concentrated below 3 GHz, and the spectrum resources
have been extremely crowded. The communication system working in the high-frequency band
has rich spectrum resources available and is more likely to occupy a wider continuous frequency
band for communication, thereby meeting the requirements of 5G on channel capacity and
transmission rate. Therefore, in November 2015, the World Radiocommunication Conference
WRC-15, in addition to determining 470~694/698 MHz, 1427~1518 MHz, 3300~3700 MHz, and
4800~4990 MHz as important frequencies for 5G deployment, It has also been proposed to study
several frequency bands within 24.25~86GHz in order to determine the frequency bands needed

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for future 5G development.
5G will have two bands of low-frequency band and millimeter wave, and the wavelength of
millimeter wave is very short and the loss is very large, so in 5G communication, we must solve
this problem.
5G low-frequency band: mainly refers to the frequency band below 6GHz.
Recently, the Ministry of Industry and Information Technology issued a draft opinion indicating:
The 3.3G-3.40GHz frequency band is basically confirmed as the 5G frequency band and is limited
to indoor use in principle;
In the 4.8G-5.0GMHz frequency band, the specific frequency allocation is determined according
to the needs of the operator.
The 4.4G-4.5GMHz band is added, but it cannot cause harmful interference to other related radio
services.
5G high-frequency band: mainly refers to the frequency band above 20GHz.
China is mainly collecting opinions in the high-frequency bands of 24.75-27.5GHz and 37-42.5GHz,
and the test is mainly carried out at 28GHz in the world.
Millimeter wave mobile communication also has shortcomings such as short transmission
distance, poor penetration and diffraction capability, and vulnerability to the climatic
environment. Therefore, high-gain antenna arrays with adaptive beamforming and beam steering
capabilities are naturally the key technologies for 5G applications in the millimeter range.
However, considering the above-mentioned system, the actual application scenario and
application environment of the antenna array, when the 5G base station with the Massive MIMO
antenna array is built, the volume of the antenna array cannot be large due to the limited space.
When the physical size of the antenna array is limited, the mutual coupling and interference
between multiple antenna elements will inevitably lead to the degradation of the antenna
performance, mainly in the following aspects:
(1) The antenna side lobes are relatively high, which has a great influence on the beam scanning
capability of the array;
(2) The signal-to-noise ratio is deteriorated due to mutual interference between the antenna
elements, which directly affects the data throughput rate;
(3) The energy that enables effective radiation is reduced, resulting in a decrease in antenna array
gain and low energy utilization efficiency.
In summary, in the low-frequency band and high-frequency band applicable to 5G, it is urgent to
find an effective theory and design method for improving the performance of the space-limited
Massive MIMO antenna array, which can reduce the size of the antenna array and maintain the
original Antenna array performance.
The first solution is a substrate integrated antenna (SIA).
This kind of antenna is mainly based on two technologies: the loss caused by the medium when
the air waveguide is transmitted is small, so the air waveguide can be used for feed transmission.
However, there are several problems. Because it is an air waveguide, it is very large in size and
cannot be integrated with other circuits, so it is suitable for high-power, large-volume
applications. The other is microstrip technology, which can be mass-produced, but It is inherently
a loss of transmission medium and it is difficult to construct a large-scale antenna array.

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Based on these two technologies, a substrate integrated waveguide technology can be produced.
This technique was first proposed by the Japanese industry. In 1998, they published the first
paper on waveguide structure for dielectric integration. It was mentioned that the waveguide
was realized on a very thin dielectric substrate, and the electromagnetic waves were blocked by
small columns to avoid Expanded on both sides. It is not difficult to understand that when the
distance between the two small columns is the one-quarter wavelength of the small fish, the
energy will not leak out, which can form high efficiency, high gain, low profile, low cost, easy
integration, low loss Antenna.
This scheme is suitable for the application of millimeter waves on the base station, and there is
another scheme on the mobile terminal.
The second solution is to design the antenna in a package integrated antenna (PIA).
Because the biggest problem with the antenna on the chip is that the loss is too large, and the
size of the chip itself is small, the design of the antenna will increase the cost, so it is almost
impossible to obtain large-scale applications in engineering. If the antenna is designed with a
package (larger than the chip) as a carrier, not only a single antenna but also an antenna array
can be designed, which avoids the limitation in size, loss, and cost of the directional antenna on
the silicon.
In fact, the antenna can be designed not only inside the package but also at the top, bottom and
around the package. Another point to be aware of is whether the PCB can be used as an antenna.
The answer is yes. The key bottleneck is not the material itself, but the design and processing
problems that the material brings. However, the PCB is only suitable for the frequency band
below 60 GHz, and LTCC is recommended after 60 GHz, but after 200 GHz, LTCC also has a
bottleneck.
To sum up
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
a 5G mobile communication system key technology. 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.