Introduction

Antenna transmission theory

In order to ensure the transmission efficiency of the antenna, the length of the antenna is about 1/4 of the wavelength of the electromagnetic wave, so the lower the signal frequency, the longer the wavelength, the longer the length of the antenna; the higher the signal frequency, the shorter the wavelength, and the shorter the length of the antenna. The commonly used 2.4 GHz band has a high frequency, a short wavelength, a short antenna length, an internal antenna, and an external antenna. The antenna can be made shorter, such as 1/8 wavelength or 1/16 wavelength, but it can be used, but the efficiency will drop. Some devices use the "short antenna + LNA" method to achieve long antenna reception. However, in order to achieve the long-wave antenna transmission effect, the short antenna needs to increase the transmission power. Therefore, the intercom needs to transmit signals, which are long external antennas, and the FM radio only receives and transmits the antenna. For example, 2G (900MHz), 4G (700-2600MHz), WIFI and Bluetooth (2.4GHz), GPS (1.5GHz), these common IoT communication methods can be used as built-in antennas.

For small-sized products such as handsets, wearable designs, and smart homes, external antennas are rarely used, and built-in antennas are commonly used. The integration is high, the appearance of the product is more beautiful, and the performance is slightly weaker than the external antenna. Internet of Things, intelligent hardware products, to network transmission of data, you need to have an antenna. The smaller the space and the more the frequency band, the more complicated the antenna design. External antennas are generally standard products, buy the right frequency band, no need to debug, plug and play. For example, the express cabinet and the vending machine generally use a magnetic external antenna and can be sucked on the iron casing. These antennas cannot be placed inside the metal cabinet, and the metal shields the antenna signal, so it can only be placed outside. The advantage is that it is easy to use and cheap, and the disadvantage is that it cannot be used in small size products.

Antenna type

There are ceramic antennas, PCB antennas and spring antennas. Ceramic antennas and PCB antennas are built-in antennas, spring antennas are external antennas.

1. ceramic antenna

Ceramic antenna

The working principle of the ceramic antenna is to use GPS satellite to realize navigation and positioning, and the main task of the user's receiver is to extract the pseudorandom noise code and data code in the satellite signal to further calculate the position, speed and time of the receiver carrier ( PVT) and other navigation information, the principle of ceramic antenna should be divided into two parts: one is the transmitting antenna, and the other is the receiving antenna. The general antennas are reversible and can be used as both a transmitting antenna and a receiving antenna. The ceramic antenna transmitting antenna simply means that a high-frequency electric field formed between the antenna and the ground is converted into an electromagnetic wave by an electrode called an "antenna", so that it can be emitted and transmitted to a distant place. The ceramic antenna receiving antenna simply means that an electromagnetic wave transmitted from the air is induced into an electric field by an electrode called an "antenna", and a high-frequency signal voltage is generated and sent to a receiver for signal processing. High-frequency, low-noise amplifiers are used in the design of ceramic antenna elements to reduce the thermal noise of the antenna and the influence of the previous stages of unit circuits on the performance of the receiver. The role of the ceramic antenna is to transform the electromagnetic energy of the radio signals transmitted from the satellite. The receiver electronics can take up the applied current, so the size and shape of the antenna is important because these determine the ability of the ceramic antenna to acquire weak electromagnetic signals.

The ceramic antenna is a small-sized antenna suitable for use in Bluetooth devices. The most used in IoT products are GPS, Bluetooth, and GSM ceramic antennas. The ceramic antenna is divided into a block ceramic antenna and a multilayer ceramic antenna. The block antenna is used to sinter the entire ceramic body at a high temperature and then print the metal portion of the antenna on the surface of the ceramic block. The multilayer antenna is fired by low-temperature co-firing, and the multilayer ceramic is laminated and then sintered at a high temperature, so the metal conductor of the antenna can be printed on each layer of the ceramic dielectric layer according to design requirements, so that it can be effective. Reduce the size of the antenna and achieve the purpose of hiding the antenna.

Since the ceramic itself has a higher dielectric constant than the PCB board, the use of a ceramic antenna can effectively reduce the size of the antenna. In terms of dielectric loss, ceramic dielectrics also have less dielectric loss than PCB boards, so they are well suited for use in Bluetooth modules with low power consumption. The size of the ceramic antenna is generally equivalent to the 1210 package, and the effect is stronger than the on-board antenna. It is also convenient to use. Generally, there are ANT access pins and feet. When designing the PCB, the antenna must be cleaned around the antenna. Pay special attention to the fact that copper cannot be applied. At the same time, when using ceramic antennas, pay attention to the matching problem of the balun circuit. If a dedicated integrated circuit is used, it is best to let the manufacturer test the matching between the balanced circuit and the ceramic antenna. If the match is not good, it will also affect the effect of the antenna.

The advantage of the ceramic antenna is that it takes up little space and has better performance. The disadvantage is that it is difficult to achieve multiple frequency bands, so it is difficult to apply to 4G products. The board has a relatively high clearance requirement and is not suitable for particularly compact products.

PCB antenna

PCB antenna

A PCB antenna refers to a portion of a PCB for wireless reception and transmission. When transmitting, it converts the high-frequency current of the transmitter into a space electromagnetic wave; when receiving, it converts the electromagnetic wave acquired from the space into a high-frequency current input receiver.

When using a PCB antenna, pay attention to the matching problem of the balun circuit. If a dedicated integrated circuit is used, it is best to let the manufacturer test the matching between the balanced circuit and the PCB antenna. If the matching is not good, it will affect the antenna. Effective PCB antennas are widely used in module boards on single frequency bands such as Bluetooth modules, WIFI modules, and ZIGBEE modules.

The advantage is that the space is less occupied, the cost is low, the antenna is not separately assembled, the touch is not easy to be damaged, and the whole machine is convenient to assemble, but the performance is sacrificed. The disadvantage is that the single antenna field type is difficult to round, the insertion loss is high, the efficiency is relatively low, and it is easy to be interfered by the main board; at the same time, it is only suitable for a single frequency band, such as Bluetooth, wifi; the performance of different batches of PCB antennas will be certain deviation.

External antenna

External antenna

The external antenna is mainly connected to the external antenna by directly soldering to the antenna (ANT) pin, IPEX interface or SMA interface. The IPEX antenna interface and the SMA antenna interface are an interface for the RF circuit and the antenna, and are widely used in wireless. A board on a LAN related product.There are many types of external antennas, such as spring antennas, FPC antennas, short glue stick antennas, long bendable antennas, and suction cup antennas.

The advantage of the external antenna is that the field type can be better controlled, the insertion loss is low, the direction of the signal is good, the efficiency is high, the anti-interference ability is strong, the interference on the main board can be reduced, and there is not much debugging matching, if any If the wireless transceiver device and the external antenna do not match, it can also be solved by directly replacing the external antenna, without replacing the PCB board; the disadvantage is that the cost is high and the assembly is troublesome.

Application

Below are application on E73 series module

Ebyte E73 series module

Parameter of E73 Module

From the above table, the difference between E73-2G4M04S1A, E73-2G4M04S1B, E73-2G4M08S1C, E73-2G4M04S1D can be clearly seen. First, the four models adopt different chip schemes, size and power E73-2G4M04S1A, E73-2G4M04S1B and E73-2G4M04S1D is the same, E73-2G4M08S1C is slightly different; but under the same test conditions, but from the transmission distance, E73-2G4M08S1C relative to E73-2G4M04S1A, E73-2G4M04S1B and E73-2G4M04S1D these three models The transmission distance is slightly better, and the transmission power will be slightly larger.

In particular, the E73-2G4M08S1C has a transmit power of 8dBm, which is a bit larger than other Bluetooth modules, so the transmission distance is slightly longer than that of other Bluetooth products.

If the IPEX antenna interface is used to access the external antenna, the transmission distance must be relative to the onboard antenna, and the transmission distance will definitely be further. If you consider the size and installation requirements, and the transmission distance is also within the acceptable range, the onboard PCB antenna or ceramic antenna is more popular. But determining a wireless transceiver is not just a transmission distance parameter, but more about the performance of the product and the different applications in different environments. Therefore, whether it is for the E73 series, or for other Bluetooth, ZigBee, GPRS products of Chengdu Yibite, it has the necessary use environment, and can choose different 2.4GHz antennas according to the needs of its own projects.