Under the trend of Internet of Everything, wireless communication module has become an indispensable part of all kinds of 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 bring out the best performance of the antenna.
With the progress of technology, in order to save the development cycle, many manufacturers have introduced a variety of finished antennas. However, if engineers do not choose the right antenna, it will not only fail to achieve the desired effect, but also waste a lot of time and cost on debugging, which is not worth the loss. In this article, we will introduce the common types of antennas and combine them with the actual use of experience in the project to give design suggestions for your reference.
Next, we will introduce the common types of antennas for you.
(1) PCB type antenna: PC etched and made of low cost, but the performance is limited adjustability can be used in large quantities for Bluetooth, WiFi wireless communication module.
(2) T patch type: commonly used ceramic antenna, occupies an area of less, high integration, easy to replace, suitable for small space requirement products, but the antenna can be used in large quantities for Bluetooth, WiFi wireless communication module.
Space requirements for small products, but the price of this type of antenna is a little expensive and the bandwidth is small.
(3) External rod antenna: good performance, no need to debug, easy to replace, high gain, suitable for a variety of terminal equipment.
(4) FPC antenna: connected by feed line, free installation, high gain, usually can use adhesive backing to stick on the machine non-metal.
Shell, suitable for high performance requirements and shell space is sufficient on the product.
The role of the antenna is to radiate the RF signal into the free space, this time to choose the right antenna for the transmission distance has a great impact. Antennas are very sensitive to the surrounding environment, and in many cases, even if the right antenna is selected, the desired effect cannot be achieved. As some customers are not clear about the factors to be considered in antenna design, here we give some experiences in actual engineering design, so that customers can better design their own circuits and PCBs, and increase the chance of success of the project.
1、 Matching circuit design
In the schematic design, you need to reserve a π-type network between the antenna and the module RF output pin. The impedance of the antenna is affected by
PCB laying, antenna installation and the surrounding metal and other factors, reserve this network is to match the antenna to 50 ohms when it is seriously deviated from the 50 ohms impedance. x1, x2, x3 are reactance components, if the antenna is a standard 50 ohms impedance, then x2, x3 can be unsoldered, x1 connected to the 220PF capacitor or 0 ohms resistor. In the PCB design, these three devices have been placed as close as possible to the RF output pins of the module and connected with short and straight transmission lines. Matching components around the 1.5mm area do not pave the ground to reduce the impact of parasitic parameters on the matching circuit.
2、 Microstrip line design
In PCB design, as most of the antenna and module output impedance is 50 ohms, in order to minimize the reflection of energy in the transmission process, RF output pin to the antenna between the PCB lead should be 50 ohms of microstrip line. Commonly used plate for 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 through the actual debugging to complete the design of the microstrip line.
3. Influence of metal on antenna
If there are metal objects near the antenna, the metal can reflect electromagnetic waves, which will not only affect the actual space of the antenna, increase the loss resistance of the antenna, reduce the radiation efficiency, and lead to the deterioration of the antenna's radiation performance. Be careful when installing the antenna:
a: The antenna should be at least 5mm away from the battery;
b: The antenna should be at least 4mm away from the shielding shell;
c: in the need to install the shell of the occasion, do not use in the shell surface with metal components of the spray paint or plating.
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