Correlation and Non-Orthogonality Figures of Merit of Beamforming Fields

New figures of merit are introduced to characterize the correlation and the non-orthogonality of multiple beams produced by an array antenna or two different array antennas. The figures of merit take into account the correlation or non-orthogonality between beamforming fields of two separate arrays and the beams produced by each at once. As an example, two adjacent modified microstrip Franklin array antennas have been designed. The non-orthogonality and isolation between steered radiation patterns have been studied for arrays operating at the same center frequencies 77 GHz. Each array antenna consists of 5 linear sub-arrays with 10 rectangular microstrip patch elements. Chebyshev tapering and open circuit stubs have been applied to the microstrip patches to obtain a low side lobe level and better impedance matching between single elements, respectively. The achieved peak gain, minimum side lobe level (SLL) and impedance bandwidth are 14.1 dBi, -13.6 dB and 581 MHz for a single sub-array at 77 GHz, respectively. The evaluation has shown that the same pair of arrays have different non-orthogonality depending on the propagation channel. On the one hand, the evaluated array-pair shows highly uncorrelated performance in a rich isotropic multipath propagation environment. On the other hand, they show high non-orthogonality (or co-directionality ) in a pure line-of-sight channel as expected. Hence, depending on the propagation channel, the arrays can be used for different communication and sensing applications either jointly or independently.