RF EMF Exposure Compliance of mmWave Array Antennas for 5G User Equipment Application

In the millimeter-wave bands towards 5G, human exposure to radio frequency (RF) electromagnetic field (EMF) is evaluated in terms of free space power density, rather than specific absorption rate. Maximum power density emitted by 5G user equipment should not exceed the power density limits set by relevant regulatory guidelines. In this paper, we provide upper bounds of maximum power density of array antennas. When the total transmitted power of array antennas is constant, calculating the maximum power density of a particular averaging area can be solved by an eigenvalue decomposition. When the power output of each port is amplitude-constrained, the power density maximization problem can be relaxed to a semi-definite program. The maximum power density can be assessed by using different assessment methods. The maximum assessed power density can also be solved by an eigenvalue decomposition or a semi-definite relaxation. The results of maximum permissible transmitted power suggest that, for the ICNIRP limits, slight deviation is observed between different types of excitation conditions including unconstrained, uniform, and dynamic amplitudes; for the proposed FCC limits, more restrictive power constraints on each port can lead to higher maximum permissible transmitted power. We provide better methods than the traditional Monte Carlo method for RF EMF exposure compliance of 5G user equipment that contains array antennas with many possible excitations. The obtained results provide valuable insights for the standardization of RF EMF exposure compliance procedures of 5G user equipment.