Experimental verification of degrees of freedom for co-located antennas in wireless channels

In English It has been postulated that six co-located orthogonally polarized electrical and magnetic dipoles can offer up to six degrees of freedom (DOFs) in a multipath scattering environment. In other words, a six-fold increase in channel capacity can be achieved in the context of MIMO systems. However, due to the complexity in designing and measuring such a six-port antenna, to our knowledge, no experimental verification has yet been successfully performed. In this paper, the six DOFs hypothesis is experimentally verified at 377MHz. The experiment involves the design and fabrication of two six-port arrays. In particular, one array is made compact with co-located antenna elements enclosed in a small cubic volume of (0.24*wavelength)^3. Using the two arrays, MIMO channel measurements are performed in a RF shielded laboratory in order to measure a multipath scattering environment. Analysis on eigenvalues of the measured channel shows that six DOFs are attained due to the orthogonality in radiation patterns of the two arrays.