@article {Electronic_Letters_2004, title = {Approximate closed-form expression for the ergodic capacity of polarisation-diversity {MIMO} systems}, journal = {Electronic Letters}, volume = {40}, number = {19}, year = {2004}, month = {September}, pages = {1192{\textendash}1194}, author = {P{\'e}rez, Jes{\'u}s and Ib{\'a}{\~n}ez, Jes{\'u}s and Vielva, Luis and Santamar{\'\i}a, Ignacio} }