Solutions to EMC of 5G Base Station Antenna - Part II

- Jul 13, 2020-

(Continued)

2. Coupling Interference Between Different Frequency Antenna Elements

In 2G, 3G, 4G and 5G multi-band base station antennas, due to the different bands and sizes of each sub-array and their compact layout on the same reflector, strong differ-frequency coupling interference is caused, which not only results in the deterioration of isolation between antenna arrays, but also causes the distortion of radiation pattern of antenna arrays, which seriously affects the signal coverage and communication quality.


Filtering technology is often used differ-frequency decoupling between antennas. For the traditional filter antenna, the isolation of the differ-frequency ports between the antenna elements can be improved mainly through the cascaded filter circuit between the radiation unit and the feed port, and blocking the coupling current into the antenna port. However, this method is difficult to achieve another important index of the base station antenna, the antenna radiation pattern preservation. In multi-band and multi-array base station antenna, the radiation pattern distortion of high-frequency antenna is caused by high-frequency induced current on low-frequency antenna. The traditional filter antenna can only cut off the path from the induced current to the low-frequency antenna port, but not removing the high-frequency induced current on the radiation unit of the low-frequency antenna. The secondary radiation of this current causes the distortion of the radiation pattern of the high-frequency antenna.


Solutions to EMC of 5G Base Station Antenna

1. Solutions to the Co-frequency Coupling Interference

In 2017, Professor Ke-Li Wu's team of the Chinese University of Hong Kong (CUHK) proposed an array-antenna decoupling surface (ADS) technology, which can effectively reduce the coupling interference between co-frequency antenna elements. This technology can overcome radiation pattern distortion in neutralization-line technique, and its decoupling bandwidth can cover 5G C-band.


2. Solutions to Differ-frequency Coupling Interference

As a new filtering technology, stealth antenna can be used to solve the problem of differ-frequency coupling interference of 5G multi-frequency multi-array common-aperture base station antenna, which cannot be realized by traditional filter antenna. The stealth antenna technology mainly includes: 1) the antenna radiator is segmented to reduce the radar cross section (RCS) of the antenna, and the band stop unit is loaded at the segmented position for band stop filtering; 2) the decoupled structure is loaded on the antenna radiator to make the induced current on the radiator in the opposite direction and the radiation offsets each other.


In 2019, Professor Y. Jay Guo's team of the University of Technology Sydney (UTS) proposed a multi-frequency array antenna with cross band scattering suppression characteristics. The antenna consists of a low-frequency antenna unit and two high-frequency sub-arrays.


In recent years, Professor Chu Qingxin's team of South China University of Technology (SCUT) has also done a lot of work on stealth antenna. The notch antenna is formed by loading an open resonant ring on the radiation unit, which can realize the differ-frequency decoupling of multi-array base station antennas.


Conclusion

Multi-band and multi-array common-aperture base station antenna is an important development direction of 5G base station antenna, and the decoupling between antenna elements, especially the antenna radiation pattern preservation is the key and difficult point of research. At present, the proposed decoupling technology cannot meet the needs of broadband base station antenna decoupling due to its narrow working band. Therefore, how to realize broadband decoupling is an urgent task.

(Translated from Microwave RF network WeChat APP)