Out-of-band interference in 5G mmW multi-antenna transceivers

Large antenna arrays used for compensating the millimeter wave (mmW) path loss gives interesting perspectives for considering out-of-band emissions and reception signals to be direction dependent. In addition, co-existence of lower frequency and mm W systems set special requirements for both conventional cellular and mm W systems. This paper presents discussion on these two cases as the most important out-of-band interference scenarios in fifth generation systems. Effects of inter modulation and adjacent channel leakage are discussed in both mm W beamforming transceiver and receiver, respectively. It is concluded that distortion is behaving differently in multi-antenna transmitter that at the receiver. Over-the-Air (OTA) measured and simulated examples of the nonlinear behavior of an array are given for receiver and transmitter, respectively. Furthermore, smart array linearization scheme given as a reference provides new perspective to consider the direction dependent out-of-band distortion as a part of the future cellular standards.