The antenna module device (antenna) is an energy converter that converts the guided waves propagating on the transmission line into electromagnetic waves propagating in the unbounded medium, or vice versa. For designing a low-power, short-distance 2.4GHz wireless transceiver device used in a radio frequency system, the design and selection of the antenna is an important part. A good antenna system can optimize the communication distance. There are many types of 2.4GHz antennas, and different applications require different antennas.
Introduction to gain antenna
In order to ensure the transmission efficiency of the antenna, the length of the communication antenna is approximately 1/4 of the wavelength of the electromagnetic wave. Therefore, the lower the signal frequency, the longer the wavelength, and 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 2.4GHz frequency band has high frequency, short wavelength, and short antenna length. Internal antennas or external antennas can be used. Antennas made shorter, such as 1/8 wavelength or 1/16 wavelength, can also be used, but the efficiency will decrease. Some devices will use the "short antenna + LNA" method to achieve the reception effect of a long antenna. However, in order for a short antenna to achieve the same transmission effect as a long antenna, the transmission power needs to be increased. Therefore, walkie-talkies need to transmit signals, which are all long external antennas, while FM radios only receive but not transmit, and have built-in receiving antennas. For example, 2G (900MHz), 4G (700-2600MHz), WIFI module and Bluetooth module (2.4GHz), GPS (1.5GHz), these common 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 commonly used. The integration level is high, the product appearance is more beautiful, and the performance is slightly weaker than the external antenna. The Internet of Things and smart hardware products require antennas to transmit data over the Internet. The smaller the space and the more frequency bands, the more complex the antenna design is. External antennas are generally standard products. If you buy one with the appropriate frequency band, no debugging is required, just 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 a metal cabinet. The metal will block the antenna signal, so they can only be placed outside. The advantage is that it is easy to use and cheap, but the disadvantage is that it cannot be used on small-sized products.
Antenna category
So how to choose a 2.4GHz antenna that is suitable for your wireless transceiver equipment from many 2.4GHz antennas? Next, we will introduce how to choose a 2.4GHz antenna through the classification and classification comparison of 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 internal antennas, and spring antennas are external antennas.
- Ceramic antenna
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 the pseudo-random noise codes and data codes in the satellite signals to further calculate the position, speed and time of the receiver carrier ( PVT) and other navigation information, the principle of ceramic antenna 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. Simply put, the ceramic antenna transmitting antenna converts 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. Simply put, the ceramic antenna receiving antenna uses an electrode called an "antenna" to induce electromagnetic waves from the air into an electric field, generate a high-frequency signal voltage, and send it to the receiver for signal processing. A high-frequency, low-noise amplifier is used in the design of the ceramic antenna unit to reduce the impact of the antenna thermal noise and the previous unit circuits on the receiver performance. The function of the ceramic antenna is to convert the electromagnetic wave energy of the radio signal transmitted by the satellite. The size and shape of the antenna is important because the receiver electronics can absorb the applied current, as these determine the ability of the ceramic antenna to pick up weak electromagnetic signals.
Ceramic antenna is a miniaturized antenna suitable for use with Bluetooth devices. The most commonly used ceramic antennas in IoT products are GPS, Bluetooth, and GSM ceramic antennas. Ceramic antennas are divided into block ceramic antennas and multi-layer ceramic antennas. The block antenna uses high temperature to sinter the entire ceramic body at one time and then prints the metal part of the antenna on the surface of the ceramic block. The multi-layer antenna is fired using a low-temperature co-firing method. The multi-layer ceramics are stacked and aligned and then sintered at high temperature. Therefore, the metal conductor of the antenna can be printed on each ceramic dielectric layer according to the design requirements, which can effectively Reduce the size of the antenna and achieve the purpose of hiding the antenna.
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, ceramic media is also smaller than the dielectric loss of PCB circuit boards, so it is very suitable 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 onboard antenna. It is also more convenient to use. It usually has ANT access pins and ground pins. When designing the PCB, there must be clear space around the antenna, and special attention must be paid not to apply copper. At the same time, when using ceramic antennas, you should also pay attention to the matching problem of the balun circuit. If you are using a dedicated integrated circuit, 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 very little space and have relatively good performance. The disadvantage is that it is difficult to achieve multiple frequency bands, so it is difficult to apply in 4G products. The requirements for circuit board clearance are relatively high and are not suitable for particularly compact products.
- 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 space electromagnetic waves; when receiving, it converts the electromagnetic waves obtained from space into high-frequency current and inputs it into the receiver. When using a PCB antenna, you should also pay attention to the matching of the balun circuit. If you are using a dedicated integrated circuit, it is best to ask the manufacturer to test the matching of the balanced circuit and the PCB antenna. If the matching is not good, it will also affect the antenna. Effective.
PCB antennas are widely used in single-band module circuit boards such as Bluetooth modules, industrial-grade WIFI modules, ZIGBEE modules, and lora modules.
The advantages are that it takes up less space, is low-cost, does not require separate antenna assembly, is not easy to be damaged by contact, and is easy to assemble, but it will sacrifice performance. The disadvantage is that it is difficult to achieve a rounded field pattern of a single antenna, with high insertion loss, relatively low efficiency, and easy to be interfered by the motherboard; at the same time, it is only suitable for a single frequency band, such as Bluetooth modules and wifi modules; the performance of different batches of PCB antennas will vary. There is a certain deviation.
- External antenna
The external antenna is mainly connected to the external antenna by directly welding on the antenna (ANT) pin, IPEX interface or SMA interface. The IPEX antenna interface and SMA antenna interface are interfaces used as radio frequency circuits and antennas, and are widely used in wireless On the single board of LAN related products.
There are many types of external antennas, such as spring antennas, FPC antennas, short glue stick antennas, long bendable antennas, suction cup antennas and other external antennas. The advantages of an external antenna are better field control, low insertion loss, good signal directionality, high efficiency, strong anti-interference ability, can reduce interference from the motherboard, and does not require too much debugging and matching. If there is The mismatch between the wireless transceiver device and the external antenna can also be solved by directly replacing the external antenna without replacing the PCB board; the disadvantage is that the cost is higher and the assembly is more troublesome.