Fundamental Limitations for DOA Estimation by a Sphere

In English In this paper we consider fundamental limitations for DOA estimation with
arbitrary lossless antennas or antenna arrays inserted inside a sphere. Spherical
vector modes and their associated equivalent circuits and Q factor approximations
are employed as a general framework for the analysis. The
classical broadband matching theory by Fano is extended to a general multiport
S–parameter model of the antennas and fundamental bounds are given
for the scattering parameters with respect to bandwidth and electrical size
of the sphere. Finally, assuming a statistical signal model with Gaussian
receiver noise, the Cramer–Rao lower bound is used to derive fundamental
upper bounds for the performance of DOA estimation by a sphere.