rsity and dual-stream MIMO. Initial network deployments will be 2 X 2 or 4 X 2 in the downlink. In order to work effectively, the two receive antennas must have similar gain and high isolation, preferably better that 10 dB, and their far-field radiation pattern must be orthogonal. If these requirements are not satisfied, the signal received from antenna 2 will be very similar to that from antenna 1, and SO the receiver will not be able to see two independent channels created by the multipath environment, collapsing into a single stream MISO (multiple-input and single-output) transmit diversity system. Wireless User Hardware For a typical handset-size device, designing a MIMO antenna system is not particularly challenging in the upper frequency bands. However, in the lower frequency bands (<1 GHz), the requirements are very difficult to achieve due to the small size of the device compared to the wavelength. The root of the problem is the same as the one causing the limited bandwidth. In general, a separation of about a quarter wavelength between two antennas is required to achieve a good isolation and low pattern correlation. Although apparently this requirement can be met even at 700 MHz (quarter-wavelength = 107 mm) in a 100-mm long device, for instance placing the antennas at opposite ends of the device, this result is just apparent. In fact, as described above, both antennas will excite the same or a very similar radiation mode on the main PCB of the device, being the counterpoise for both antennas, resulting in very similar (dipole-like) radiation patterns with high correlation (close to 1). 26 In general, the best that can be achieved is to excite two radiation modes aligned with each diagonal of the main PCB: the two resulting dipole patterns will be skewed by an angle about 40-50 degrees, resulting in an envelope correlation coefficient about 0.3, which might be sufficient. The isolation of the antenna will depend on the details of the antenna designs, and methods are available increase the isolation, for 