For a long time, whether it is a smart phone, a laptop, or a tablet, Bluetooth is the standard configuration of smart devices. With the development of the mobile Internet, a large number of smart wearable devices are now emerging, and supporting the development of these applications requires not only the support of mobile software, but also the support of wireless sensor technology. Bluetooth is still the preferred communication method for wireless connections.
In hardware design, the antenna design is more particular. The commonly used low-cost design method is the PCB on-board antenna design method, but how should the PCB on-board antenna be designed in practice to achieve a good transmission and reception effect? There are four bluetooth antenna designs below for reference.
The antenna body of the inverted-F antenna can be linear or sheet-shaped, and the size of the Bluetooth antenna can be reduced when an insulating material with a higher dielectric constant is used.
As a kind of on-board antenna, the inverted-F antenna of Bluetooth antenna design has low cost but adds a certain volume, and it is the most common one in practical applications.
The antenna is generally placed on the top layer of the PCB, and the ground is generally placed on the top layer and near the antenna, but the ground must not be placed around the antenna, and the surrounding area should be a clear space.
The length of a meandering antenna is more difficult to determine. The length is generally slightly longer than a quarter wavelength, and its length is determined by its geometric topological space and coverage area.
The meander antenna is generally a PCB package, that is, an on-board antenna. Like the inverted F type, the meander antenna of the Bluetooth antenna design is generally placed on the top layer of the PCB, and the floor is generally placed on the top layer and near the antenna. However, the ground must not be placed around the antenna, and the surrounding area should be a clear space.
Ceramic antenna is another small antenna suitable for Bluetooth devices. The types of ceramic antennas are divided into bulk ceramic antennas and multilayer ceramic antennas.
Since the dielectric constant of the ceramic itself is higher than that of the PCB circuit board, the use of a ceramic antenna can effectively reduce the size of the antenna. In terms of dielectric loss, ceramic medium is also smaller than that of PCB circuit boards, so it is very suitable for use in Bluetooth modules with low power consumption. When designing the PCB, there should be clearance around the antenna, and special attention should be paid to not covering copper.
The 2.4G rod-shaped Bluetooth antenna is large, but the transmission distance is stronger than other antennas. When designing the PCB, there should be clearance around the antenna as well as the above-mentioned three antenna designs.
1) The antenna's signal (frequency greater than 400MHz) is easily attenuated, so the distance between the antenna and the nearby ground must be at least three times the line width.
2) For microstrip lines and strip lines, the characteristic impedance is related to the thickness, line width, vias and dielectric constant of the plate.
3) Vias will produce parasitic inductance, and high-frequency signals will cause very large attenuation. Therefore, try not to have vias when the Bluetooth antenna is routed through the radio frequency line.