Worst-Case Estimate of Envelope Correlation Coefficient for Small MIMO Mobile Antennas Below 1 GHz

Abstract

A worst-case estimate of an envelope correlation coefficient (ECC) is obtained for small multiple-input multiple-output (MIMO) mobileantennas operating below 1 GHz. The worst-case estimate is numerically derived in this paper using spherical and exponential wavefunctions. The derived result confirms that the worst-case ECC can be easily obtained from the rotation angle between the radiationpatterns of two MIMO elements, which are attained directly from the amplitude of 2D electric field patterns without any additionalphase and polarization information. As a practical example, MIMO mobile antennas with different antenna element arrangements arecompared to verify the validity of the proposed worst-case estimate. Moreover, based on these analyses, we also suggest an effectiveapproach to reduce the ECC of a small MIMO mobile antenna operating below 1 GHz by properly locating the antenna elements tomake the radiation patterns perpendicular to each other.