24-Port and 36-Port Antenna Cubes Suitable for MIMO Wireless Communications

We describe 24-port and 36-port antennas based on a cube structure. The antennas are formed by densely packing individual antennas onto a cube. The 24-port antenna cube has a volume of 0.72 lambda
_o

³
while the 36-port antenna has a volume of 1.13 lambda
_o

³
. Even though the individual antennas are densely packed, most combinations of mutual couplings between ports exhibit better than -20 dB isolation. The basic 24-port cube antenna is formed by utilizing cross polarized quarter-wave slots at the cube edges. This provides polarization diversity on every edge of the cube, and both spatial and polarization diversities on the entire structure, leading to good isolation. Additionally 6 pairs of half-wave slot antennas are placed on each surface of the cube to provide 12 extra ports and therefore form our 36-port antenna. The cube antennas are made from FR-4 printed-circuit-boards (PCB), which is low-cost and allows ease of prototyping. The proposed cubes are investigated by simulation and measurement. One potential application for the cube antennas is in multiple-input-multiple-output (MIMO) wireless communication systems. The expected channel capacity of the 36-port cube with both mutual coupling and channel correlation considered is between 131-159 b/s/Hz at an SNR of 20 dB per receiver branch (compared to an ideal channel capacity of 197 b/s/Hz) when MIMO channels in a rich scattering environment with sufficient multipath are available.