Using a VNA Based Spherical Near Field Antenna Measurement System for Active Antenna System Performance Verifications

For diverse services and applications, it is crucial for operators to ensure better quality of experience expectations in 5G networks. State-of-the-art techniques such as beamforming schemes and massive MIMO systems are utilized to enhance spectral efficiencies and system capacities within cellular coverage areas. Those emerging technologies have been implemented in active antenna systems (AAS). Consequently, how to evaluate the performance of the AAS in radiation characteristics becomes a key issue. Therefore, we propose an over-the-air (OTA) mode near field measurement system for AAS radiation performance verifications in this paper. The radiation pattern test method of the AAS by using a vector network analyzer (VNA) based spherical near field antenna measurement system is proposed to obtain the magnitude and phase distributions of the fields at RF carrier frequency from an antenna under test (AUT) with single-tone transmitting. In order to verify the above method, a signal generator is used to provide the single-tone source into a commercial passive base station antenna. Also, two received channel connections to the VNA are included, where a reference antenna placed adjacent to the back of the AUT for phase recovery is added together with the existing probe of the spherical near field antenna measurement system for reconstructing the near-field amplitude and phase of the fields received during scanning. Thus, the near-field to far-field transformations and back projections can be performed for the active antenna performance verifications. Radiation patterns obtained from this OTA mode near field measurement method demonstrate good agreements with those from conventional near field tests at 3.5 GHz for 5G FR1 radio units.