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    2021-10-21 17:39:49
    What is a Cell Phone Antenna?


    Ⅰ Introduction
    Ⅱ Concept explanation
    Ⅲ The development of cell phone antennas
    Ⅳ Cell phone antennas in the 5G era

    Ⅰ Introduction

    The cell phone antenna is a small antenna device on the mobile phone to receive and transmit electromagnetic waves. When you use a smartphone to make calls, send text messages, play online games, etc. a series of communication behaviors every day. Have you ever considered that the phone's antenna module is responsible for all of this? The smartphone will become a stand-alone game console if there is no antenna.

    cell phone antenna.jpg

    cell phone antenna

    The radio transmitter's radio frequency signal power is transferred to the antenna via the feeder (cable) and radiated by the antenna as electromagnetic waves. After the electromagnetic wave arrives at the receiving location, it is followed by the antenna (only a small part of the power is received) and sent to the radio receiver through the feeder. You can see that the antenna is an important radio device that transmits and receives electromagnetic waves. Without an antenna, there is no radio communication.

    Ⅱ Concept explanation

    Antenna input impedance

    The input impedance of the antenna is the impedance value obtained by looking at the antenna end from the interface between the transceiver and the antenna. This value has a great influence on the radiation efficiency of the antenna, the fluctuation of the antenna's in-band gain, and the power capacity of the antenna's front end.

    Working frequency and working bandwidth

    The bandwidth of the antenna refers to the range of the frequency band. The operating frequency refers to all frequencies within the bandwidth of the antenna. Multiple indicators limit the working bandwidth. Therefore, the narrowest bandwidth among them needs to be selected. In mobile phone antennas, the bandwidth defined by factors such as directional pattern bandwidth and polarization bandwidth is greater than the impedance bandwidth. Therefore, in mobile phone antennas, the bandwidth range that meets the required standing wave is generally used as the working bandwidth of the antenna.

    Beam pattern

    The antenna beam pattern describes the relationship between the energy radiated by the antenna and any position in space. Through the pattern, we can know the relative or absolute intensity of the electromagnetic wave radiated by the antenna at each position in space. There is no doubt that the horizontal pattern of the cell phone antenna should be omnidirectional. In fact, the beam pattern of the cell phone antenna is not important. The radiation characteristics of the cell phone antenna and the radiation characteristics of a single antenna are not the same. The pattern of the cell phone antenna only requires that the horizontal plane is approximately omnidirectional.

    Directivity and antenna gain

    The directivity of an antenna is related to its beam pattern, so the directivity is also a function of the azimuth angle, which is defined as follows: D(θ,ψ)=[radiation intensity of the antenna in the (θ,ψ) direction]/[omnidirectional antenna Radiation intensity]

    Because the radiation efficiency of the antenna itself must be considered, the antenna gain is usually to replace the directivity. The relationship between the two is:


    The radiation efficiency of the antenna is related to the amount of energy lost in the electromagnetic wave radiation process.

    The energy loss that may occur during the process of energy transmission and reception of the antenna includes energy reflection caused by impedance mismatch at the antenna input, energy loss caused by the material of the antenna itself at high frequencies, and consumption in the propagation medium energy. The gain of the cell phone antenna does not represent the efficiency of the cell phone. The indicator that really represents the antenna gain characteristics should be the average effective gain of the antenna. It is related to the use environment, usage mode, cell phone structure, and cell phone design method of the cell phone antenna.

    Ⅲ The development of cell phone antennas

    The earliest big cell phone antenna was an external antenna, which was a low-frequency analog signal antenna. 

    Built-in antennae were utilized by NOKIA in the 2G period, which was stamped from thin stainless steel sheets. Later, in order to reduce costs, FPC (printed circuit boards) appeared. FPC is characterized by its soft material and can be attached to curved surfaces. It has advantages over metal antennas in terms of space utilization. FPC antennas are still the mainstream antenna technology until now.

    Built-in antenna.png

    Built-in antenna

    With the development of technology, the LDS antenna technology came into being. It is to directly engrave the antenna with a laser on a specially processed plastic molding material. We can see this technology in current mid-to-high-end cell phones. 

    MIMO technology

    Multi-input Multi-output (MIMO) is an abstract mathematical model that describes a multi-antenna wireless communication system. It can use multiple antennas at the transmitting end to send signals independently. Using multiple antennas at the receiving end and restoring the original information is a concept of space-division multiplexing.

    Without increasing bandwidth or total transmission power consumption, MIMO can dramatically enhance data throughput and transmission distance. The primary concept of MIMO is to make use of the spatial freedom given by many transmitting and receiving antennas to increase the spectrum efficiency of a wireless communication system, resulting in higher transmission rates and better communication quality.

    MIMO technology can be used in wireless communication networks to communicate with base stations. It can also be used in WiFi networks to communicate with wireless routers. We usually use A*B MIMO to indicate the number of antennas. For example, 2*2 MIMO means 2 channels of transmission and 2 channels of reception. Its theoretical transmission capacity is twice that of SISO.

    It is expected that terminals would use a greater number of MIMO technologies in the future 5G network.

    Ⅳ Cell phone antennas in the 5G era

    The size remains the same, the quantity increases

    The antenna is an important part of wireless communication equipment. It transmits and receives electromagnetic wave signals. The antenna is a wire with a specified length, which can be manufactured on PCB and FPC.

    FPC antenna.jpg

    FPC antenna

    The wavelength of the wireless signal is strongly correlated with the antenna length. In most cases, it must be 1/4 or 1/2 of the electromagnetic wavelength. The electromagnetic wavelength of the 900Mhz frequency band in the 2G era, for example, is 20-30cm, while the antenna size is roughly 7.5cm.

    The current 4G communication band is 0.8-2.6GHz, and the main communication frequency band used by 5G is also below 6GHz. Therefore, there will be no major changes in the size of cell phone antennas using the 5G Sub-6G frequency band. It will remain at the centimeter level.

    However, 5G will employ additional antennas, or MIMO technology, in order to meet increased speed needs. For example, 4×4 MIMO has 4 transmitter antennas and 4 collector antennas.

    The increase in the number of antennas will require the shape of multiple antennas to be re-arranged, putting new requirements on the back cover and wiring of the cell phone to achieve better efficiency. The Huawei Mate30 Pro 5G has a total of 21 antennae, 14 of which are 5G antennas.

    Difficulties of cell phone antenna design in the 5G era

    There are two 5G frequency bands, low frequency, and high frequency. The low-frequency band is 3~5Ghz. It is similar to the current 4G band, and the antenna can follow the current design. However, in order to meet the 5G transmission rate requirements, the number of antennas must be increased.

    We can solve that problem by using MIMO multi-antenna technology in the low-frequency band. But it doesn't work in the high-frequency band. As mentioned above, the higher the frequency, the shorter the wavelength. In the 5G high-frequency band, the communication wavelength is only about 10mm (millimeter wave). Physics tells us that the shorter the wavelength, the greater the transmission attenuation.

    R&D personnel said that fingers and faces will have a "proximity effect" in front of the 5G millimeter-wave antenna. Not only will it cause the signal to drop, but it may also even directly shield the signal.

    However, the greater challenge is yet to come.

    Today's popular full-screen design will become the biggest challenge for antenna design in the 5G era. The most difficult aspect of the full-screen design is not the screen design, but the antenna design. Generally speaking, the antenna in the cell phone radiates 360° in all directions. It is necessary to avoid metal in a certain range near it. This range is the "clearance zone".

    The clearance area of antennas is often on the "chin". However, the full-screen design greatly reduces the area of the "chin". And a whole metal screen completely covers the front of the phone, which places very high requirements on the antenna design.

    Specifically, because 5G millimeter waves are very short, interference from metals will be more serious, requiring at least a 1.5mm headroom. When the hand or face is blocking the phone, the phone signal will start looking for the lowest bit error rate frequency band. Therefore, when designing a 5G terminal, the antenna installation location must be appropriate from the beginning.

    In addition to receiving performance, space coverage and heat dissipation issues must also be considered. The wider the spatial coverage, the more conducive to the user's wireless experience, but the wider the spatial coverage, the design of the cell phone is often sacrificed. In addition, in order to prevent damage to the antenna system due to improper heat dissipation, we should pay attention to the control of materials when designing the whole machine.

    The challenges brought about by 5G antenna design are likely to force manufacturers to abandon the metal back cover and change the shape and size of the fuselage. If you don't have an intuitive impression of this, then take a look at the latest 5G module of Moto Z3, and you will have the answer.

    Solution-antenna array

    The difficult antenna design does not mean that smartphones in the 5G era will definitely become ugly. The smartphone market in the 5G era may usher in a new round of reshuffles. Truly powerful manufacturers will stand out and continue to provide consumers with products with good looks and functions.

    In fact, 5G antenna design is difficult. But it doesn’t mean that there are not solutions. At present, the industry is generally optimistic about the antenna array (multi-antenna unit) design. That is to say, an antenna system composes of many identical single antennas arranged according to a certain rule.

    The current 5G millimeter-wave antenna arrays are generally based on phased arrays. There are specific implementation methods including AoB (Antenna on Board, that is, the antenna array is located on the system motherboard), AiP (Antenna in Package, that is, the package where the antenna array is located on the chip Inside), and AiM (Antenna in Module, that is, the antenna array and RFIC form a module). At present, the AiM method is the main trend.

    AiM's millimeter-wave antenna arrays generally use complementary radiation beams (such as broadside radiation, or wide-side radiation, and end-fire radiation, or end-fire) antenna types (such as patch antennas) to achieve wider spatial coverage. It is based on the appropriate design of the antenna feed point, to achieve dual-polarization (vertical and horizontal polarization) coverage, thereby greatly improving the range of millimeter-wave signals and coverage.

    The switching of multiple antenna arrays may also cause another problem. Switching from an antenna array with weaker performance to a gap between an antenna array with higher performance may miss a large amount of data and cause a significant decrease in user connection experience. Based on this, whether to switch the antenna array and how to shorten the time for switching the antenna array requires the cooperation of hardware engineers and software engineers, which can test the manufacturer's skills.

    In addition, the small-size phased antenna array design helps to reduce the 5G antenna's need for internal space and antenna clearance area. Therefore, it achieves a more compact body design and a higher proportion of the screen.  Qualcomm released The QTM052 millimeter wave antenna module in October 2020. It is 25% smaller than the previous generation, further reducing the space occupied by the 5G antenna on the cell phone.

    The 5G era is a brand-new era. Not only antenna design, the network layout based on 5G, the ecological chain based on 5G, and the application scenarios based on 5G all pose new challenges for smartphone manufacturers. Fortunately, challenges are also opportunities. In the 5G era, truly capable manufacturers will surely stand out and achieve a new leap in the new era.

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