Communication antenna device (antenna) is an energy converter that converts the guided wave propagating on the transmission line into an electromagnetic wave propagating in an unbounded medium, or vice versa. For designing a low-power, short-distance 2.4GHz wireless transceiver used in a radio frequency system, the design and selection of the antenna is an important part. A good antenna system can achieve the best communication distance. There are many types of 2.4GHz antennas, and different applications require different antennas.

Gain Antenna Introduction

To ensure the transmission efficiency of the antenna, the length of the communication 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 antenna length; the higher the signal frequency, the shorter the wavelength, the shorter the antenna length. The commonly used 2.4GHz frequency band has a high frequency, a short wavelength, and a short antenna length. It can be built-in or external. The antenna can be made shorter, such as 1/8 wavelength or 1/16 wavelength, and it can also be used, but the efficiency will decrease. Some devices will use the "short antenna + LNA" method, which can also achieve the receiving effect of a long antenna. However, in order for a short antenna to achieve the transmitting effect of a long antenna, it is necessary to increase the transmitting power. Therefore, walkie-talkies need to transmit signals, and they all have long external antennas, while FM radios only receive but do not transmit, and have built-in receiving antennas. For example, 2G (900MHz), 4G (700-2600MHz), WIFI module and BLE modules (2.4GHz), GPS (1.5GHz), these commonly used IoT communication methods can be used as built-in antennas.

For small-sized products such as handheld devices, wearable designs, and smart homes, external antennas are rarely used, and built-in antennas are generally used. The integration is high, the product appearance is more beautiful, and the performance is slightly weaker than that of external antennas. The Internet of Things and smart hardware products need antennas to transmit data online. The smaller the space and the more frequency bands, the more complex the antenna design. External antennas are generally standard products. Buy the ones with the right frequency bands, no debugging is required, and they are plug-and-play. For example, express cabinets and vending machines generally use magnetic external antennas, which can be attached to the iron shell. These antennas cannot be placed inside the metal cabinet, as the metal will shield the antenna signal, so they can only be placed outside. The advantages are that they are easy to use and cheap, but the disadvantage is that they cannot be used on small-sized products.

2. Antenna categories

How to choose a 2.4GHz antenna suitable for your wireless transceiver device from a large number of 2.4GHz antennas? Next, we will introduce how to choose a 2.4GHz antenna by classifying and comparing 2.4GHz antennas. Antennas used in the 2.4GHz frequency band mainly include ceramic antennas, PCB antennas, and spring antennas. Ceramic antennas and PCB antennas are built-in antennas, and spring antennas are external antennas.

1. Ceramic antennas

The working principle of ceramic antennas is to use GPS satellites to achieve navigation and positioning, and the main task of the user's receiver is to extract pseudo-random noise codes and data codes from satellite signals to further solve the navigation information such as the position, speed and time (PVT) of the receiver carrier. The principle of ceramic antennas can be divided into two parts: one is the transmitting antenna, and the other is the receiving antenna. General antennas are reversible and can be used as transmitting antennas and receiving antennas at the same time. The transmitting antenna of a ceramic antenna is simply to convert the high-frequency electric field formed between the antenna and the ground into electromagnetic waves through an electrode called an "antenna", so that it can be emitted and transmitted to a distant place. The receiving antenna of a ceramic antenna is simply to convert the electromagnetic waves transmitted from the air into electric fields through an electrode called an "antenna", generate high-frequency signal voltage, and send it to the receiver for signal processing. In the design of the ceramic antenna unit, a high-frequency, low-noise amplifier is used to reduce the impact of antenna thermal noise and the previous unit circuits on the performance of the receiver. The role of the ceramic antenna is to convert the electromagnetic wave energy of the radio signal transmitted from the satellite into current that can be absorbed and applied by the receiver electronic devices. Therefore, the size and shape of the antenna are very important, because these determine the ability of the ceramic antenna to obtain weak electromagnetic wave signals.

Ceramic antenna is a miniaturized antenna suitable for use in BLE devices. The most commonly used in IoT products are GPS, BLE, and GSM ceramic antennas. Ceramic antennas are divided into block ceramic antennas and multilayer ceramic antennas. Block antennas are made by sintering the entire ceramic body at high temperature and then printing the metal part of the antenna on the surface of the ceramic block. The multi-layer antenna firing adopts the low-temperature co-firing method to stack and align the multi-layer ceramics and then sinter them at high temperature. Therefore, the metal conductor of the antenna can be printed on each layer of the ceramic dielectric layer according to the design requirements. In this way, the size of the antenna can be effectively reduced and the purpose of hiding the antenna can be achieved.

Since the dielectric constant of ceramic itself is higher than that of PCB circuit board, the use of ceramic antenna can effectively reduce the size of the antenna. In terms of dielectric loss, the dielectric loss of ceramic dielectric is also smaller than that of PCB circuit board, so it is very suitable for use in BLE modules with low power consumption. The size of ceramic antenna is generally equivalent to 1210 package, and the effect is stronger than that of on-board antenna. It is also convenient to use. Generally, there are ANT access pins and ground pins. When designing PCB, the area around the antenna must be cleared, and special attention should be paid to not plating copper. At the same time, when using ceramic antennas, attention should also be paid 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 of the balanced circuit and the ceramic antenna. If the matching is not good, it will also affect the effect of the antenna.

The advantages of ceramic antennas are that they take up little space and have better performance. The disadvantage is that it is difficult to achieve multi-band, so it is difficult to use in 4G products. The clearance requirements for the circuit board are relatively high, and it is not suitable for particularly compact products.

2. PCB antenna

PCB antenna refers to the part on the PCB used for wireless reception and transmission. When transmitting, it converts the high-frequency current of the transmitter into electromagnetic waves in space; when receiving, it converts the electromagnetic waves obtained from space into high-frequency current input into the receiver. When using PCB antennas, you should also 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 of the balanced circuit and the PCB antenna. If the matching is not good, it will also affect the effect of the antenna.

PCB antennas are widely used in single-band module circuit boards such as BLE modules, industrial-grade WIFI modules, ZIGBEE modules, lora modules, etc.

The advantages of PCB antennas are that they take up less space, are low in cost, do not need to assemble the antenna separately, are not easy to touch and damage, and are easy to assemble the whole machine, but they will sacrifice performance. The disadvantage is that it is difficult to make a single antenna field round, the insertion loss is high, the efficiency is relatively low, and it is easy to be interfered by the motherboard; at the same time, it is only suitable for a single frequency band, such as BLE modules and wifi modules; the performance of PCB antennas in different batches will have certain deviations.

3. External antenna Antenna

External antennas are mainly connected by directly welding on the antenna (ANT) pin, IPEX interface or SMA interface. IPEX antenna interface and SMA antenna interface are interfaces for RF circuits and antennas, and are widely used on single boards of wireless LAN related products.

There are many types of external antennas, including spring antennas, FPC antennas, short rubber stick antennas, long bendable antennas, suction cup antennas and other external antennas. The advantages of external antennas are better field control, low insertion loss, good signal directionality, high efficiency, strong anti-interference ability, and can reduce interference from the motherboard. There is no need for too much debugging and matching. If there is a mismatch between the wireless transceiver and the external antenna, 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 it is more troublesome to assemble.

4. Application of 2.4G antenna

Taking Chengdu EBYTE's E73 series BLE module as an example, introduce the comparison of different 2.4G antenna module types

As shown in Table 1, E73-2G4M04S1A, E73-2G4M04S1B, and E73-2G4M04S1D are compatible with IPEX antennas and PCB antennas. The default interface is PCB antenna, and E73-2G4M08S1C uses a ceramic antenna.

From the table above, we can clearly see the differences between E73-2G4M04S1A, E73-2G4M04S1B, E73-2G4M08S1C, and E73-2G4M04S1D. First, the four models use different chip solutions. The size and power of E73-2G4M04S1A, E73-2G4M04S1B and E73-2G4M04S1D are the same, and E73-2G4M08S1C is slightly different; but under the same test conditions, in terms of transmission distance, E73-2G4M08S1C has a slightly better transmission distance and a slightly larger transmission power than E73-2G4M04S1A, E73-2G4M04S1B and E73-2G4M04S1D.

It is particularly important to point out that the transmission power of E73-2G4M08S1C is 8dBm, which is larger than other BLE modules, so the transmission distance is slightly longer than that of other BLE products.

If the IPEX antenna interface is used to connect an external antenna, the transmission distance will definitely be longer than that of the onboard antenna. If the volume and installation requirements are taken into consideration, and the transmission distance is within an acceptable range, the onboard PCB antenna or ceramic antenna is more popular. However, the determination of a wireless transceiver device is not only the transmission distance parameter, but more importantly, the performance of the product and different applications in different usage environments. Therefore, whether it is for the E73 series or for other wireless data transmission module products such as BLE modules, ZigBee modules, and GPRS modules of Chengdu EBYTE, there are necessary usage environments, and different 2.4GHz antennas can be selected according to the needs of their own projects.

Chengdu EBYTE is a high-tech enterprise in the field of wireless transmission applications in the Internet of Things, and a national gazelle enterprise. At present, Ebyte has independently developed hundreds of patent inventions, mainly including the research, development, production and sales of wireless communication equipment such as ZigBee modules, lora wireless modules, WiFi modules, BLE modules, 4GGPRS/NBIOT/can/dtu and other wireless data transmission modules and data transmission radios, remote control switches, industrial routers, serial port servers, industrial signal transmission, power modules, antenna equipment, etc. Provide customers with various technical support and case studies.