Peculiarities of adaptive signal processing in circular antenna arrays

Abstract

Formulation of the problem. Today, antenna arrays are often used as directional antennas of different radio systems. The main advantages of the such antennas over the mechanically steered directional antennas are the ability to steer the main lobe (beam) of the Radiation Pattern (RP) without the rotation of the array, and also the ability to control the shape of the RP. However, the antenna arrays also have some drawbacks. For example, a drawback of the linear and the planar antenna arrays is the varying beamwidth. This width increases as the orientation of the beam moves from the normal to the aperture to the plane of the aperture. This feature is due to the fact that when the beam is deflected, the effective aperture of the antenna array decreases, and this is the reason of the beam increase. If it is required to steer the beam in a wide range of angles while maintaining its width, then this restricts the usage of a linear and flat antenna arrays as the directional antennas. This disadvantage is practically absent in the circular antenna arrays. Therefore, such arrays are attractive for the usage, for example, in the radio communication systems, because they allow the beam to move within 360° in azimuth plane while maintaining its width practically fixed. If the antenna array is built using a digital beamforming architecture (digital array), then such an array can also be easily made as a multi-beam one, that will provide a parallel view of space. In multibeam digital antenna arrays, the same analog portion of each channel from the antenna to the digital output is used to form all the beams. And only in digital form, the separate devices for the forming of these beams are required, which multiply the channel output signal samples by the weights and add the weighted signals together to form the output signals of the antenna array. The access to the signals from the outputs also allows such an antenna array to easily become adaptive, because these signals are used to calculate the weights in all the adaptive algorithms. The adaptive signal processing allows to suppress the interferences. The suppression of the interference signals in the output signal of the antenna array is achieved due to the creation of the dips (low levels) in the RP towards the sources of these interferences. Such a change in the shape of the RP is provided by the changing weights calculated using an adaptive algorithm. Target. The paper deals with the circular adaptive antenna arrays with digital beamforming. The features of the such adaptive antenna arrays and their performance are considered. Results. The architecture of a single beam and a multibeam adaptive antenna array is considered, as well as a procedure (algorithm) for the calculation of its weights. It is also demonstrated the efficiency of a circular adaptive antenna array in terms of maintaining its beamwidth regardless of its direction and simultaneously suppressing interferences, that practically does not affect this beamwidth. Practical significance. The considered adaptive antenna array can be used as a directional antenna in radio systems where it is required to form a several beams simultaneously, to maintain their width regardless of steering directions, and also to suppress the interference signals in the output signal.