Impact of lossy feed on S-parameter based envelope correlation coefficient

Envelope correlation coefficient is a key parameter for MIMO antennas, allowing assessment of the signal correlation between multiple input/outputs of an antenna system. A simplified method allows calculation of this coefficient by using only S-parameters, however the method is less accurate and only applies to lossless antennas. This paper discusses a possible correction to the above method, for the case where the losses occur in the feed cable and not in the antenna itself. A lossless MIMO antenna system with lossy feeds is discussed, both analytically and using simulation tools. It is shown, that even losses as small as 0.3 dB can lead to substantial underestimation of the coefficient. A new equation is proposed, which compensates for the lossy feeds. It is also demonstrated, that even for a lossless case, some discrepancies exist between the two commonly used methods to calculate envelope correlation coefficient.