An antenna is an energy converter that converts guided waves propagating on a transmission line into electromagnetic waves propagating in an unbounded medium, or vice versa. Regarding the design of a low-power, short-range 2.4GHz wireless transceiver device used in a radio frequency system, the design and selection of the antenna is an important part. An excellent antenna system can optimize the communication distance. There are many types of 2.4GHz antennas, and different applications require different antennas.
Antenna Introduction
To ensure the transmission power of the antenna, the length of the 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 normally, but the power will be reduced. Some devices will use the “short antenna LNA” method, which can also achieve the reception effect of a long antenna. However, in order for a short antenna to achieve the same transmitting effect as a long antenna, the transmitting 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 and Bluetooth (2.4GHz), GPS (1.5GHz), these common IoT communication methods can be used as built-in antennas.
For small-scale 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 function 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 will be. 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 in small-scale products.
Antenna category
So how to choose the 2.4GHz antenna that is most suitable for your wireless transceiver equipment from many 2.4GHz antennas? Next, we will introduce how to correctly select 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.
(1) Ceramic antenna
The working principle of ceramic antennas is to use GPS satellites to complete 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 the 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 a transmitting antenna and a receiving antenna 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. To put it simply, 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 weaken the impact of the antenna thermal noise and the previous unit circuits on the receiver performance. The function of the ceramic antenna is to transform the electromagnetic wave energy of the radio signal transmitted from the satellite. Replacement electronic devices can absorb the current used, so the size and shape of the antenna are very important, because these determine the ability of the ceramic antenna to obtain strong electromagnetic wave signals.
Ceramic antenna is a miniaturized antenna suitable for use in 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 the metal part of the antenna is printed on the surface of the ceramic block. The multi-layer antenna uses 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 accurately printed on each ceramic dielectric layer according to the design requirements. In this way It 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 antenna size. 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 1210 and the package is appropriate, and the effect is stronger than the on-board 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 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 function of the antenna.
The advantages of ceramic antennas are that they take up very little space and have relatively good functions. The disadvantage is that it is difficult to achieve multiple frequency bands, so it is difficult to use in 4G products. The requirements for circuit board clearance are relatively high and are 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 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 a dedicated integrated circuit is used, 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. Functional.
Many PCB antennas are used on single-band module circuit boards such as Bluetooth modules, WIFI modules, and ZIGBEE modules.
The advantages are that it takes up less space, is low-cost, does not need to be assembled separately, and is not easy to be damaged by contact. The whole machine is easy to assemble, but it will sacrifice performance. The disadvantage is that a single antenna field pattern is difficult to round, the insertion loss is high, the power is relatively low, and it is easily interfered by the motherboard; at the same time, it is only suitable for a single frequency band, such as Bluetooth and WiFi; the performance of different batches of PCB antennas will vary error.
(3) 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. on the single board of wireless 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 external antennas are better field control, low insertion loss, good signal directionality, high power, strong anti-interference ability, which can reduce interference from the motherboard, and does not require too much debugging and matching. If there is a mismatch between the wireless transceiver device 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 higher and it is more troublesome to assemble.
Related keywords: Remote measurement and control terminal