Linearization Trade-Offs in a 5G mmWave Active Phased Array OTA Setup

The new generation of 5G mobile communication systems is using millimeter wave (mmWave) active phased arrays (APA) which have up to hundreds of individual analog transmitter and receiver chains and antennas. For these highly integrated systems linearization of each analog path is very challenging. Therefore a single input single output (SISO) system in combination with over the air (OTA) measurement is considered as an efficient approach for linearization. However, the knowledge about the dependency of the total SISO nonlinearity on the contributions from different blocks in the antenna array, as well as the linearization trade-offs is still missing. In this paper, an overview of the possible linearization trade-offs in an OTA setup with a mmWave APA is provided. The linearization technique is applied to a $4\times 4$ active phased array containing up-conversion of a sub 6 GHz LTE10 signal to an RF frequency of 28 GHz. Through measurements, the effects on adjacent channel power ratio (ACPR) and error vector magnitude (EVM) have been investigated for the following scenarios: i. impact from the up-converter, ii. impact of the steering angle due to antenna crosstalk and iii. a linearity comparison between a linearized and a backed-off system.