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Describe in detail the development of mobile phone antenna

2024-04-25 Update From: SLTechnology News&Howtos shulou NAV: SLTechnology News&Howtos > IT Information >

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Do you know how many wireless communication systems a cell phone has? According to the specifications of mobile phones, we analyze the wireless communication systems supported by mobile phones. Smartphones today can support up to seven wireless communication systems, and each includes many wireless bands. Cellular communication alone is the most basic wireless function of mobile phones, and there are more than 60 frequency bands covering 2G, 3G, 4G and 5G. It has to be said that today's smart phones are really the most elite design of electronic devices, using the highest chip manufacturing technology, supporting the most complex wireless environment, and also super cattle cameras, game consoles, audio and video players.

I have to give our correspondent a thumbs up and a big like.

The above picture is a functional diagram of a smart phone. Now the development of chip technology allows a mobile phone to achieve such complex functions in a small volume. The RF transceiver module is also integrated into several small RFICs, but what about the antenna? Such RF devices, which are strongly correlated with electromagnetic wavelengths, are difficult to shrink into ICs and support so many frequency bands.

Let's explore together today how the mobile phone antenna is reduced to the mobile phone bit by bit?

No.1, the first mobile phone antenna What is the earliest mobile phone antenna? First of all, the earliest mobile phone antennas must have been used on the earliest mobile phones. At the Barcelona Communications Show in 2023, Martin Copper, winner of the GLOMO Personal Lifetime Achievement Award, is the inventor of the current mobile phone, and the first real mobile phone is the mobile phone in front of Martin in the picture below. It was at Motorola Labs that Martin got his first mobile phone.

See, the long pole on the top of the mobile phone head is the first mobile phone antenna, the scientific name is monopole antenna, commonly known as whip antenna.

Monopole antennas are one of the oldest forms of antennas, and were used in Marconi's transatlantic communications. The transmitting antenna applied by Marconi is a sector structure formed by 50 copper wires obliquely pulled from a 48m high horizontal wire, which can be considered as the first practical monopole antenna. The oscillation source is a spark generator of 70Hz, and then a square single cone antenna is formed by using 4 wooden towers to erect a wire network. As shown in the figure, the transmitting wavelength is 1000m.

Then, with the increase of radio operating frequency, the wavelength of electromagnetic wave is shorter and shorter, and the size of monopole antenna is smaller and smaller. For a long time, monopole antenna is a common antenna for wireless equipment.

In 1944, Motorola applied for the first patent for mobile communication equipment (patent number: US2439411A), monopole antenna appeared on the patent application, and this patent is not very similar to the later mobile phone.

The monopole antenna has simple structure and convenient tuning. Its size is only half of that of dipole antenna with the same operating frequency. Its working principle diagram is shown in the figure below. One arm of monopole antenna, which can be equivalent to infinity, realizes double-arm radiation of dipole antenna by means of mirror image.

If the ground of a monopole antenna is infinite, its radiation pattern is half that of a dipole.

But mobile devices cannot provide an infinite ground, so the actual directivity pattern of a monopole antenna varies. The following is the antenna directivity pattern obtained by changing the size of the monopole antenna ground using simulation software. Is it strange that as the monopole antenna ground becomes smaller and smaller, its directivity pattern becomes closer and closer to the dipole?

This vertical monopole antenna provides a perfect omnidirectional radiation pattern in the horizontal direction, which is very beneficial for mobile phone applications. But in the vertical direction is not good, especially in the axis, there is a large radiation pit, the signal does not go to this pit inside. So, you must not point your WiFi antenna at your mobile phone...

However, the large size is too beautiful, so engineers think about how to miniaturize the monopole, the more common scheme is to make the monopole radiation line spiral to compress the volume of the antenna. Or it's made into a stretched structure that shrinks when not in use.

This method of reducing the size of monopole antennas by using helical lines has also been widely used in mobile phones. For example, in early Motorola and Nokia phones, the antenna became a small radish head.

Then can the monopole antenna be folded up and packaged directly in the mobile phone?

No.2 Invisible mobile phone antenna monopole antenna vertical can be used, then folded up can be used? So there's the first step to artificially modifying the monopole.

Can coaxial monopole antenna be made into microstrip monopole antenna? Of course, it is possible, and microstrip monopoles can also be bent to make inverted L-shaped monopoles.

We know that the characteristic impedance of dipole antenna is 73.1 ohms, and the characteristic impedance of monopole antenna is half of dipole antenna, which is about 36.5 ohms. In the design process, we need to match the impedance of 50 ohms feed line that we usually use. In order to further improve the impedance matching of the inverted L monopole, antenna engineers added a grounding point in front of the inverted L feed to make an inverted F-shaped antenna, which is often seen as an IFA antenna. Further, the radiation part of IFA is realized by a flat plate to improve the bandwidth of the antenna, and a planar inverted-F antenna PIFA appears.

The diagram below shows an evolution of a monopole antenna.

The following figure shows a basic structure of planar inverted-F antenna. The radiating element of monopole evolves into a large radiating plate, which is placed above the antenna ground. At a position near the feed point, the radiating plate is short-circuited through a short-circuit via to achieve impedance matching. Planar inverted-F antenna needs a thicker structure to realize, which is most widely used in Nokia mobile phones. Motorola mobile phones of the same era are still more keen on inverted-L or IFA antennas, which may also be one of the factors that Motorola mobile phones are always thinner than Nokia.

Nokia 3210 is the first mobile phone to use PIFA antenna. In 1987, Nokia launched the first mobile phone Nokia Mobira Cityman, still using a long pole as a mobile phone antenna, slowly shrinking the antenna into a small radish head, in 1999, on the Nokia3210, the antenna was finally fully integrated into the mobile phone, users can not see. The Nokia3210 also became the best-selling device in mobile phone history, with total sales of 160 million units.

In the disassembly report provided by IFix website, we finally found the true face of this PIFA antenna, and it is not clear whether the hole in the middle is its short circuit point.

Of course, in 2000, the mobile communication network was relatively simple, Nokia 3210, the best-selling mobile phone in history, also only supported GSM and DCS bands, Bluetooth, Wifi, satellite navigation and other most basic wireless functions on smart phones, all of which were 0.

The network environment is relatively simple, the antenna design is not too complicated, and the usual dual-band antenna can meet the communication requirements of mobile phones. Now, a mobile phone only needs to support more than 60 frequency bands to meet basic cellular communication functions, covering almost all frequency bands currently used by 2G, 3G, 4G and 5G, as well as wireless communication requirements for Bluetooth, Wifi and satellite bands.

No.3 smart phone antenna now mobile phone support wireless communication bands more and more, the antenna is needed more and more, the easiest way is to put each antenna needed, such as Palm on the back of the phone integrated GPS antenna, and GSM low frequency 900MHz and high frequency 1800MHz antenna, and in the upper right corner also added an extension antenna.

For a long time, mobile phone antennas have been set up like this, and printing antennas on plastic back covers is a good design in terms of cost and space utilization. This antenna is pulled out with an external metal sheet or other structure to achieve the antenna, that is, FPC antenna.

Apple has used this FPC antenna from the first generation of Apple phones to the iPhone 3GS, which uses plastic film to seal copper film to make flexible antennas and place them inside the plastic shell of the phone.

In 2010, Apple launched the Iphone4, which brought revolutionary changes to the antenna design of mobile phones. For the first time, the metal frame of mobile phones was used as a radiator, and the antenna design and structural parts were perfectly integrated, creating an era of frame antennas.

The main antenna of the iPhone 4 phone is not only on the side of the case, but combined with another antenna inside the phone. The sides of the chassis are welded with complex metal sheets to support multiple bands in different countries.

This brand-new antenna design was once on the hot search because of the "antenna door," many users reported that "when holding the iPhone 4 with your hand, the signal of its mobile network will completely attenuate to the level where you can't talk within minutes. "

The reason is also very clear, the frame antenna is directly exposed to the outside of the mobile phone, very easy to be interfered by the outside world, especially when holding the phone, first, the dielectric constant of the human body will change the working frequency of the antenna, affecting the antenna effect; second, this method of setting different working frequencies of the antenna through the breakpoint, if the human body happens to touch the breakpoint, because the human body is a conductor, it is easy to make the breakpoint invalid.

However, it doesn't matter if there is a problem, just solve it. What is most afraid is that the problem encountered on the iPhone 4 is afraid of encountering problems, which is quickly solved by Apple's antenna engineers, and the solution is very simple. On the iPhone 4S launched later, we see that a breakpoint is added to the frame, and the mobile phone signal is perfectly revived.

In any case, this kind of frame antenna greatly promotes the progress of Mobile device antenna, and also inspires a new idea of Mobile device antenna design: the integration of antenna and structure function. On Huawei's Mate60, I also noticed that the camera frame was also designed as an antenna-NFC antenna.

The specific design of Apple mobile phone frame antenna, there is no specific information found at present, in the paper "Overview of Future Antenna Design for Mobile Terminals" detailed introduction of mobile phone metal frame antenna design structure and principle. By cleverly dividing and grounding, various antenna designs such as inverted L antenna, inverted F antenna and loop antenna can be realized in the metal frame to meet the requirements of multi-band and multi-system of mobile phones.

The development of mobile phone antenna, first introduced here, any questions, comments or + V private chat.

references

1,https://tisc.njust.edu.cn/e/f3/41/c12098a258881/page.htm;

2,https://link.springer.com/chapter/10.1007/978-3-642-22543-7_21;

3,https://finance.sina.cn/2022-09-15/detail-imqqsmrn9174393.d.html;

4,https://zhuanlan.zhihu.com/p/58163329;

5,https://zhuanlan.zhihu.com/p/100421364

6,https://zhuanlan.zhihu.com/p/58163329

7, 5G Mobile device antenna design

This article comes from Weixin Official Accounts: RF School (ID: RF_Center), author: RF Little Carpenter

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