Digital pattern synthesis with a compact MIMO antenna of half-wavelength diameter

Abstract

The paper presents a compact multiport antenna, with beamforming capabilities and a realized gain of 4.31 dBi with the size of λ/2. The antenna allows digital beamforming with independent control over three parameters: main-beam direction, beamwidth, and null-depth. Those parameters can be dynamically adjusted within a continuous range, create multiple beams for different frequency channels, and simultaneously generate multiple digital patterns. Due to digital beamforming capabilities, the proposed antenna offers much greater flexibility over switch-based analogue beamforming of Electronically Steerable Parasitic Array Radiator (ESPAR) antennas. The reconfiguration properties are achieved by using superposition of three dipole-like radiation patterns, where each radiator generates different spherical mode, i.e. with different angular phase distribution in the horizontal plane. This allows beamsteering with compact size, while the use of different modes ensures low Envelope Correlation Coefficient (ECC) from 10−4 to 3.2 × 10−5 for the operating frequency of 2.4 GHz. The proposed technique allows for significantly greater pattern reconfiguration than any reconfigurable antenna or array of comparable size and is a perfect candidate for Software Defined Radios.