A Descriptive Model for Analyzing the Diversity Performance of Compact Antenna Arrays

Mutual coupling has negative impact on the radiation properties of compact antenna arrays when the spacing of individual radiators is considerably closer than half a wavelength. We have previously put forward a description of the radiation efficiency of an arbitrary antenna array in terms of orthogonal radiating eigenmodes. The present publication elaborates on this concept and presents a descriptive equivalent circuit model for a coupled antenna array. We show that eigenmodes undergo independent Rayleigh fading under appropriate conditions. Also, we demonstrate how practical closed-form expressions in terms of the array's scattering matrix can be derived, which characterize the diversity performance and therefore are convenient measures for the radiation quality of a compact antenna array.