Spatial aliasing effects on beamforming performance in large-spacing antenna array

In the next wireless communication generation, 5G, the half-lambda inter-element spacing as high-resolution antenna array is usually employed due to its benefits i.e., minimum grating lobes and providing one end-fire maximum. However, to compensate the lower aperture from a such short-spacing elements, the number of antennas should be grown larger. It will be costly and increase the complexity in terms of antenna array analysis. In this paper, the aliasing effects on beamforming of antenna array geometry utilizing inter-element spacing more than half-lambda is presented. The geometry of linear, circular and planar antenna arrays will be explored and simulated at center frequency of 60 GHz. It is also due the fact that many researchers working on 5G believe that 60 GHz will be employed as 5G frequency band. The frequency of 60 GHz is truly higher than today long-term-evolution (LTE) working frequency and it is really challenging to model its signal due to small wavelength and its effective signal working distance as effect of rain attenuation, etc. As our preliminary results, linear array, which only considers the azimuthal, the spatial aliasing appears in the inter-element distance more than 1-lambda. On the other hand, the circular and planar antenna array consider the azimuth and elevation properties of incoming signals. In circular array, the angular power of a signal can be detected accurately applying the 3-sector antenna pattern. When the inter-element distance grows more than 1.5 lambda, the spatial aliasing which appear as side lobes with similar angular power dominate the incoming signal detection. The result shows us that employing the 2-lambda distance or more will be useless. Planar array which actually a 2-axis linear array give the unexpected results, most of detections are inaccurate and angular power also low. This concludes that spatial aliasing effects will degrade the beamforming performance due to confusion between real signal and fake signal resulting from similar values of array factor.