The maximum achievable array gain under physical transmit power constraint

In this paper, we derive the maximum achievable array gain of a uniform linear antenna array with isotropic radiators under physical transmit power constraint in three different propagation scenarios: line-of-sight, Rayleigh fading, and constant non-line-of-sight. It turns out that the achievable array gain is larger than is claimed in previously reported results, which do not take the physical transmit power into account. We show that the maximum achievable array gain can increase proportional to the square of the number of transmit antennas for line-of-sight, and also for Rayleigh fading with not too large an angle-spread. In case of some special, constant non-line-of-sight scenarios, the array gain can even grow exponentially with the number of transmit antennas. These result are exciting, for they imply that the potential of multi-antenna communication systems can be much higher than previously reported.