What determines the communication distance of the wireless module? Selection is very important for antenna

2020-2-18whwireless

The communication distance of wireless module is an important index. How to maximize the effective communication distance has always been a puzzle for customers. In this paper, according to the debugging experience, the selection and use of the antenna are explained, hoping to help engineers quickly debug the communication distance.

The primary parameter affecting the communication distance of the wireless module is the transmission power. The transmission power of the wireless module and the corresponding ideal transmission distance can be found in the manual. On the premise that the transmission power meets the requirements, the selection of the antenna and the directionality of the antenna are considered.

The first is the selection of antenna:

The main specifications of the antenna include the following: frequency range, SWR or VSWR, antenna gain, polarization mode and impedance. The frequency range should be selected as required; the VSWR should be less than 1.5; the antenna gain also affects the transmission distance; the polarization mode can be divided into linear polarization and circular polarization; the impedance needs to match the output impedance of the wireless module, generally 50 ohms. Pay special attention to VSWR parameters here. It is better to test SWR with network analyzer after purchasing antenna.

The comparison table of SWR, return loss and transmission power is shown in Table 1.

It can be seen from the above table that when VSWR = 1.5, the theoretical transmission power is 96%. When VSWR = 2, the transmission power is only 88.9%. Some antenna VSWR indexes are less than 2. When selecting an antenna, the best VSWR is less than 1.5, which can get higher transmission power.

Secondly, antenna directionality:

Antenna has directionality, which means that antenna has different radiation or receiving ability in different directions of space. The antenna directionality is usually measured by using a pattern. Figure 1 shows a pattern of an antenna with a frequency range from 2400mhz to 2500mhz.

When the antenna is placed vertically, the direction with the deepest red color is the direction with the strongest radiation or receiving ability of the antenna. Therefore, when installing the antenna, install the antenna in the direction with the red color as much as possible, so as to ensure good signal quality. In addition, the metal plate has a shielding effect on the signal, so there should be no metal plane in the direction of transmitting and receiving.

There are also some antenna directions shown in the manual, which are represented by two-dimensional drawings, including H-plane and E-plane, as shown in Figure 2.

When testing the communication between wireless modules, the directionality of the antenna must be considered. When the communication space is not blocked and the direction of the antenna corresponds to the strongest radiation direction, the communication distance can reach the maximum. If the antenna is not installed properly, the communication distance will become shorter, or even unable to communicate.

When testing the wireless module communication, engineers often encounter weak signal, communication distance not reaching the instructions in the manual or high packet loss rate. When it is determined that the wireless module itself is OK, engineers may test the performance of the antenna itself first, and then test in the direction of strong radiation of the antenna signal, and better test results will be obtained.