Under the trend of Internet of Everything, wireless communication module has become an indispensable part of various electronic devices, and the communication quality of the module largely depends on whether the antenna design is reasonable or not. This paper describes how to choose the right antenna and utilize the best performance of the antenna.
With the advancement of technology, in order to save the R&D cycle, many manufacturers have introduced a variety of finished antennas. However, if engineers choose improperly, not only can they not perform as well as they should, but also they will waste a lot of time and cost in investigation and debugging, and the gain will outweigh the loss. In this article, I will introduce several commonly used antennas and make design suggestions for your reference based on the practical experience of using them in your projects.
Next, I will introduce the commonly used antenna types :
(1) Board mounted PCB type antenna : Low cost with PC etching, but limited performance and good tunability. WiFi wireless communication module.
(2) T-Patch type : Commonly used ceramic antenna, small footprint, high integration, easy to replace, suitable for space
products with small space requirements, but this type of antenna is slightly more expensive and has a smaller bandwidth.
(3) External rod antenna: good performance, no need to debug, easy to replace, high gain, applicable to a variety of terminal equipment.
(4) FPC antenna: connected by feed line, free installation, high gain, machine non-metallic metal can usually be backed with adhesive paste
The shell is suitable for products with high performance requirements and sufficient shell space.
The role of the antenna is to radiate RF signals into free space. At this point, choosing the right antenna has a great impact on the transmission distance. The antenna is very sensitive to the surrounding environment, even if you choose the right antenna, it will not achieve the expected results. Since some customers do not know the factors that need to be considered for antenna design, we give some experiences in the actual engineering design, so that customers can better design their own circuits and PCBs to increase the chance of project success.
1、 Matching circuit design
When designing the schematic diagram, you need to reserve a π-type network in the antenna and module RF output pins. Antenna impedance is affected
PCB laying, antenna installation, surrounding metal and other factors, in order to match the antenna to 50 when it is seriously off 50 when the impedance of the ohm. X1, X2, X3 are reactance components, if the antenna is a standard 50-ohm impedance, so X2, X3 can not be soldered, X1 connected to the 220PF capacitor or 0-ohm resistor. In the PCB design process, these three devices are as close as possible to the RF output pin of the module, connecting the transmission line is short and straight. Matching components around 1.5mm in order to reduce the impact of parasitic parameters on the matching circuit, do not influence in the circuit.
2, microstrip line design
In the PCB in the design, the output impedance of the antenna and the module is mostly 50 ohms, in order to reduce the reflection of energy in the transmission process, RF output pins and antennas between the PCB lead should be 50 ohms of microstrip line. Commonly used plate is FR4 (dielectric constant 4.2-4.6), according to experience, when the line width of the microstrip line distance from the reference layer of 2.2 times the distance, the characteristic impedance of the microstrip line is about 50 ohms. It is recommended to use the microstrip line impedance control tool (ADS, txline, etc.) to calculate the specific design, and complete the design of the microstrip line through the actual debugging. As shown in the figure below, the grounding layer under the microstrip line must be a complete ground, and more grounding holes are required on both sides of the microstrip line.
3. The effect of metal on the antenna
If there is metal material near the antenna, the metal can reflect the electromagnetic wave, it will not only affect the actual space of the antenna, increase the loss resistance of the antenna, reduce the radiation efficiency, but also deteriorate the radiation performance of the antenna. Attention should be paid when installing the antenna:
a: The antenna should be at least 5mm from the battery;
b: The antenna should be at least 4mm from the shielding shell;
c: In the case of the need to install the shell, do not paint or coat the surface components of the shell.
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