A Compact Planar Printed MIMO Antenna Design

In this paper, we describe the design of a novel planar multiple-input-multiple-output (MIMO) antenna. The basic idea of the design is the development of a canonical two-port antenna that can be replicated and concatenated together to form MIMO antennas with arbitrary even numbers of ports. The design of the canonical element uses compact folded slots for the radiating elements but includes the use of field cancelation to enhance isolation by incorporating a coupling parasitic element. In addition by properly designing the coupling parasitic and the two-port antenna, coupling between canonical elements is also reduced allowing them to be concatenated together. The canonical element size is 27.5 × 30 mm² operating at 2.6 GHz and it can be packed together with high densities of up to 22 elements per square wavelength. To validate the design, results from 20-port planar printed MIMO antennas are presented operating at 2.6 GHz with a bandwidth of 100 MHz. The 20-port antenna has size of 1.3λ₀ × 0.69λ₀ mm² providing an antenna density of 22 antenna in free space square wavelength (λ₀²). Even though the individual antennas are densely packed, all combinations of mutual couplings between ports exhibit better than 10 dB isolation. The antennas are printed on an FR-4 printed circuit board (PCB), which is a low-cost substrate and allows straightforward prototyping.