Since the birthof wireless transmission technology, it has brought great convenience topeople. At the same time, the equipment that is inseparable from wirelessdevices is the antenna. Antennas play an important role in wireless devices.
In the previousradio stations, I have seen very familiarity in the movies. As shown in theabove figure, the power of such radio stations is generally very large. The obvioussign is that there will be a long one in the upper left. The antenna, thisantenna ensures the normal use of the radio. The picture below shows an earlymobile phone that can be seen in its upper right corner without the shadow ofthe antenna.
So what is themeaning of the antenna for wireless devices? First of all, we must start fromthe actual role of the antenna.
The antenna mainly converts the electrical signal (ie, energy) into anelectromagnetic wave signal (also a kind of energy form) to omnidirectionallyradiate or directionally radiate into space, which is the essential role of theantenna. Therefore, when the wireless device does not have an antenna, theelectrical signal will not convert the electromagnetic wave signal very well,and without the electromagnetic wave signal, the most basic wirelesscommunication cannot be realized, which is one of the reasons why the wirelessdevice has a large signal after the antenna is not reduced.
Just since I said that no antenna is one of the reasons to reduce the wirelesssignal, there are certainly other reasons. There is also a problem of impedancematching. In today's wireless devices, 50Ω (ohm) impedance matching isbasically used. That is to say, from the position of the antenna interface to thecircuit board, the equivalent resistance inside the circuit board should be 50Ω(ohm), so that the best impedance matching can be achieved, which is of coursepart of the design of the wireless high-frequency circuit. Chengdu Ebyte is doing agood job in wireless high-frequency circuit design. It has a dedicated deviceto measure the impedance problem. It is very expensive to know that this deviceis expensive.
I just said that there is no antenna and impedance problem because of thesignal reduction. Now let's talk about the antenna itself.
Antennas come in many forms, and each different form of antenna will havedifferent performance. In the simplest case, there are the following problems:
Frequency caused by:
The antenna should match the wireless operating frequency. The 2400MHzfrequency uses a 2400MHz antenna, and the 5.8GHz frequency requires a 5.8GHzantenna. If the antenna frequency does not match the actual radio frequency,the signal will be bad and the transmission distance will be short. Here, aconcept called standing wave ratio will be introduced. The frequency mismatchwill lead to an increase in the standing wave ratio.
Frequency also has problems with physical characteristics. Simply put, thelower the frequency, the better the diffraction, the higher the frequency, theworse the diffraction. This can also explain why the performance of 2.4G wifithrough the wall is better than the 5.8G WiFi signal of the same level. At thesame time, the lower the frequency, the lower the amount of data that can betransmitted. The simplest one can be explained by 2G, 3G and 4G mobile phones.The 2G era is also around 900MHz. In the 3G era, the mobile phone network speedhas increased, the frequency is around 2000MHz, and it is still around 2000MHzat 4G. It is worth mentioning that China Mobile has a TDD-LTE base station with2500MHz frequency. And only the world has this band in the world. Therefore, itcan be seen that the number of base stations in the 4G era is larger than thatof the GSM era, and it is dense. Then the problem is coming again. Both 4G and3G are at 2000MHz. Why is 4G faster than 3G? Here is the credit of the antenna.In the 4G system, there is MIMO technology, multi-transmission technology, nowthe mobile phone can be up to 4 antenna MIMO technology, and the base stationis 8 MIMO technology, that is, space division multiple access technology, heretoo The importance of the antenna to the wireless device can be seen.
Signal difference caused by environmental factors:
Everyone knows that the wireless signal is traveling in a straight line, andthe earth is a sphere. It is a garden. Therefore, it cannot transmit in thepast from point A in Asia to point B in the Americas. (Note: This is whywireless communication is carried out in two places not far apart. When theantenna is higher and the communication distance is one of the main reasons,then the wireless signal can still be transmitted normally in the past. Thereason for removing the relay station is that there is an ionosphere in theearth's atmosphere when the wireless signal is transmitted. After going out, itwill reflect in the atmosphere (there are many reflections, spatialreflections, diffuse reflections, etc.). After reflection, the B point canreceive the signal. Since it is a reflection, the reflection effect of lowfrequency is definitely better than that of high frequency according to thephysical properties of the radio frequency.
The problem of decline:
The fading problem involves the theory of free space fading. There is a freespace communication distance equation. The transmission power is PT, thetransmit antenna gain is GT, and the operating frequency is f. The receivedpower is PR, the receiving antenna gain is GR, and the transmission andreception are performed. When the distance between the antennas is R, the radiowave loss L0 in the middle of propagation has the following expression whenthere is no environmental interference:
L0 (dB) = 10 Lg ( PT / PR )
= 32.45 + 20 Lg f ( MHz ) + 20 Lg R ( km ) - GT (dB) - GR (dB)
According to this equation, wireless frequency, power, antenna performance andcommunication distance are inseparable, so the wireless device is born withoutthe antenna. Of course, there are still fading and slow fading, and fast fadingis definitely the most horrible. Another type of fading is due to reflections,such as waveguide effects, multipath fading. The actual phenomenon is that youare around a long river, the signal is actually not good, and in the forest,the signal is also very bad, the leaves will lead to a lot of multipath fading.
The problem with the antenna itself:
The problem with antennas lies in the type of antennas, and there are manytypes of antennas, Yagi antennas, mushroom antennas, dual-ridge antennas, smartantennas, ceiling antennas, and so on. There are also omnidirectional antennas,directional antennas, and high gain antennas. The lobe problem of the antennais also one of the reasons for the good or bad of the wireless signal. There isa very common saying, "Tower under the black", the word is saiddirectly below the antenna, there is basically no wireless signal, this is theworld. The electromagnetic emission method is inseparable. In the radiationdirection of the antenna, there is no lobes directly below, resulting in nosignal directly below.
The omnidirectional antenna, that is, the direction in which the antennaradiates is 360 degrees, radiates 360 degrees around the antenna vibrator, thatis, at the upper and lower ends of the antenna element, the signal is theworst. As shown in the omnidirectional antenna:
In the case ofdirectional antennas, the electromagnetic radiation of directional antennas isdirectional. It is divided into main and side lobes and back lobes. The mainlobes concentrate most of the energy. The side lobes and the back lobes aresmall. Part of the energy, which also led to the destiny of the antenna withoutsignal. As shown in Figure 1.4 directional antenna:
Of course, thequality of the wireless signal is also related to the interface of the antenna,such as SMA port, IPX interface, PCB antenna, feeder, etc. These are also oneof the reasons that affect the quality of the wireless signal.
There are many other reasons, and I won’t go into details here.
Having said that, there are antennas, and the bad antennas will bring theconsequences of communication failure. What impact will these devices have ifthere is no antenna? In the simplest case, there is no antenna, nocommunication, and the device is hot. When the device is a high-power device,according to the nature of the antenna mentioned in the above question, whenthere is a large amount of energy, it cannot be transmitted through the antennain time. It is concentrated on the board, causing the board to heat up andeventually burn out the chip. Similarly, when the antenna impedance isseriously mismatched, the antenna energy is largely reflected into the circuit.The parameter is reflected in the standing wave ratio, and the chip is heated.Burn the chip.