Four major Bluetooth antenna design methods
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This post was last edited by alan000345 on 2019-4-9 07:44 Bluetooth has always been a standard feature of smart devices, whether it is a smartphone, a laptop, or a tablet. With the development of mobile Internet, a large number of smart wearable devices have emerged. To support the development of these applications, not only mobile software support is needed, but also wireless sensor technology support is needed. Bluetooth is still the preferred communication method for wireless connection. Bluetooth technology is the most important link in this. It requires not only communication sensitivity, but also miniaturization, low power consumption, and more importantly, low cost. The emergence of Bluetooth 4.0 version solves these problems. It includes Bluetooth Smart (low power) function, which has the following characteristics: 1) Low energy consumption 2) Low cost 3) Standard button battery can keep the device running for several years 4) Multi-vendor interoperability 5) Enhanced range In hardware design, antenna design is more particular. The commonly used low-cost design method is PCB board antenna design. But how should PCB board antenna be designed in practice to achieve good transceiver effect? The following are four Bluetooth antenna designs for reference. Bluetooth antenna design - inverted F-type antenna The antenna body of the inverted F-type antenna can be linear or sheet-shaped. When using insulating materials with higher dielectric constants, the size of the Bluetooth antenna can be reduced. As a type of onboard antenna, the inverted F-type antenna has low design cost but increases a certain volume. It is the most common type 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 there should be a clear area around it. As shown below: ![]()
Figure 1: Schematic diagram of inverted F-type antenna design Bluetooth antenna design: meander antenna design The length of the meander antenna is difficult to determine. The length is generally slightly longer than a quarter wavelength, and its length is determined by its geometric topological space and the area of application. The meander antenna is generally a PCB package, that is, a board-mounted antenna. Like the inverted F type, 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 there should be a clear area around it. As shown in Figure 2, Figure 3: ![]()
Figure 2: Schematic diagram of meander antenna design 1 ![]()
Figure 3: Schematic diagram of meander antenna design 2 Note: Antenna length calculation formula: The length of the antenna (meter) = (300/f) * 0.25 * 0.96 Where f represents the frequency (MHz), 0.96 is the wavelength shortening rate The length of the Bluetooth antenna is about 300/2.4G * 0.25 * 0.96, which is about 31mm Bluetooth antenna design: ceramic antenna design Ceramic antenna is another type of miniaturized antenna suitable for use in Bluetooth devices. Ceramic antennas are divided into block ceramic antennas and multilayer ceramic antennas. Since the dielectric constant of ceramic itself is higher than that of PCB circuit boards, using ceramic antennas can effectively reduce the size of the antenna. In terms of dielectric loss, ceramic dielectrics are also smaller than the dielectric loss of PCB circuit boards, so they are very suitable for use in Bluetooth modules with low power consumption. When designing the PCB, just leave enough space around the antenna, and pay special attention to not applying copper. As shown below: ![]()
Figure 4: Schematic diagram of ceramic antenna design Bluetooth antenna design 2.4G rod antenna design The 2.4G rod-shaped Bluetooth antenna is large in size, but its transmission distance is stronger than other antennas. When designing the PCB, the area around the antenna should be cleared as in the above three antenna designs. As shown below: ![]()
Figure 5: 2.4G rod antenna design schematic diagram Other relevant points about Bluetooth antenna design: 1) The antenna 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 of the board layer, line width, vias and the dielectric constant of the board. 3) Vias will produce parasitic inductance, which will greatly attenuate high-frequency signals, so try not to have vias when running RF lines.
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