MIMO antenna arrays built on metamaterial substrates
A magnetic permeability enhanced metamaterial is used to enhance the antenna array of a Multiple Input Multiple Output (MIMO) communication system. A rectangular patch antenna array is formed including a stack of a plurality of unit cells, where each unit cell includes an inductive loop of magnetic permeability enhanced metamaterials embedded in a host dielectric substrate. The use of such metamaterials permits the antenna arrays to be made smaller, and have less mutual coupling, when using a metamaterial substrate. The measured channel capacities of the antenna arrays are similar for the metamaterial and conventional substrates; however, the capacity improvement when using MIMO relative to single antenna communication systems is greater for antennas on metamaterial substrates.
1. A method of improving the capacity and mutual coupling performance of a MIMO antenna array, comprising:
selecting N T transmitter antennas and NR receiver antennas each comprising a metamaterial substrate so as to form a resonance structure based on induced inductance of the metamaterial substrates combined with the capacitance of the metamaterial substrates;
determining a statistical description of a transmission environment including said MIMO antenna array, where the statistical description is provided in a matrix H i , where Hi is the normalized channel matrix corresponding to an i th channel realization where H i includes interference and signal to noise as a product of the location and spacing of the N T transmitter antennas and N R receiver antennas;
using the normalized channel matrix to compute the channel capacity C for each array configuration for a given subcarrier; and
placing said N T transmitter antennas and said N R receiver antennas, mounted on said metamaterial substrates, in an array configuration so that the resulting antenna array has channel capacities C that are approximately the same as channel capacities C of relatively larger antenna arrays formed without said metamaterial substrates.
2. The method of claim 1 , wherein computing the channel capacity C of each channel i is computed as:
C
=
1
N
ch
∑
i
=
1
N
ch
log
2
[
det
(
I
N
R
+
SNR
N
T
H
i
H
i
†
)
]
,
where N ch is a number of channel realizations measured at each receiver antenna position for every subcarrier, I NR is a N R ×N R identity matrix, SNR is signal to noise ratio in channel i, and H i † is a complex conjugate transpose operation.