A Multi-Port Pattern Diversity Antenna With High Isolation

A pattern-diversity antenna with 7 ports is proposed for multiple-input multiple-output (MIMO) applications. Orthogonal modes are utilized to achieve high isolation among all 7 ports in a relatively compact shared volume. As distinguishing feature from previous works, the concept of tripolarization is generalized, allowing to design antennas with a large number of orthogonal patterns in a single multi-port device. Based on this approach, a simple structure is proposed with only two printed circuit boards (PCB) separated by an air gap. The proposed multi-port antenna can provide a high degree of pattern and polarization diversity for the coverage of the whole upper hemisphere space. Measurements confirm the following results for the fabricated prototype: 7.7% impedance bandwidth, higher than 20 dB isolation among all ports with an antenna size of
$(0.61^{2} \times \pi \times 0.061) \lambda _{L}^{3}$
where
$\lambda _{L}$
is the free-space wavelength at the lowest operating frequency.