A Trigger-Free Multi-Active-Probe Anechoic Chamber System for 5G/6G Millimeter Wave OTA Test

The multi-probe anechoic chamber (MPAC) approach is one of the most promising candidates for fifth-generation (5G)-advanced/sixth-generation (6G) massive multiple-input-multiple-output (MIMO) over-the-air (OTA) performance testing. In this article, a trigger-free multi-active-probe anechoic chamber system (MAPAC) is proposed for 5G/6G millimeter wave (mmWave) OTA test, which allocates the transmitting (Tx) and receiving (Rx) probes separately and then avoids the requirement for uplink (UL)/downlink (DL) switching signals. The system architecture is proposed, and a figure of merit for the UL/DL channel reciprocity is provided. For system design, simulations are conducted on essential items, such as the measurement distance, probe density, Tx/Rx probe spacing, etc. A novel dual-polarization active probe (AP) with independent Tx and Rx antennas is developed for the test system, which has the advantages of low loss, low cost, and high integration. The accuracy of the trigger-free mmWave MAPAC is experimentally verified by 3rd Generation Partnership Project (3GPP) clustered delay line (CDL)-A and CDL-C channels with promising application potential.