Third-Order Intermodulation Effects and System Sensitivity Degradation in Receive-Mode 5G Phased Arrays in the Presence of Multiple Interferers

Electronically scanned phased-array antennas need to function in an interference-rich environment as an integral part of millimeter-wave 5G networks. In these scenarios, multiple interferers' incident from different directions can create intermodulation products that can severely degrade the system sensitivity. This paper first presents the theoretical analysis of intermodulation effects in a receive-mode phased array and then shows the detailed experimental verification of multiple interferer effects on a 28-GHz 5G phased array. It is shown that the third-order intermodulation products generated by the interferers peak at certain predictable scan angles depending on the interferer directions of arrival and can limit the sensitivity of the phased array. The interferers degrade the system sensitivity even if incident in the direction of pattern nulls. Two scan-angle-dependent third-order input intercept point (IIP3) definitions are given for a phased array and their implications are discussed. It is shown that while a phased array does result in an input P1dB improvement as the number of elements increases (handles more incident power than a single channel), it does not result in an IIP3 improvement over a single channel as the number of elements increases. Theoretical predictions are also verified by extensive numerical simulations and measurement results for multiple interferers from different directions. Finally, the IIP3 degradation in mechanically scanned antennas is analyzed and it is shown that such antennas are much more robust than phased arrays for wide angle interferers.