Electromagnetic waves in the near zone of aperture antenna grids with a square-form opening

Abstract

Relevance. The paper investigates wave phenomena in the near and intermediate zones of aperture equidistant flat antenna arrays with a square aperture with arbitrary electrical dimensions of the aperture and distances between the radiators.

Purpose - theoretical study of the behavior of the amplitude and phase of electromagnetic waves in the near and intermediate zones of aperture discrete antennas.

Materials and methods. The problem is solved by the method of superposition in electrodynamics. In the developed mathematical support, no restrictions are imposed on the shape of the opening, the geometric and electrical dimensions of the antenna, the amplitude and phase distributions of the field sources in the opening.

Results. It is shown that at distances between emitters not greater than half the working wavelength, the spatial distribution of the field in the near zone of aperture antenna arrays is close to the field distribution in the near zone of continuous aperture antennas of the optical and acoustic type. Aperture sizes that do not exceed two wavelengths, field amplitudes in the near observation zone is decrease uniformly as the distance increased. At medium (L »5¸10 wavelengths) and large electrical dimensions of the opening in the near zone of the antenna, a spotlight beam is formed, which is a weakly inhomogeneous locally plane traveling wave, the average amplitude of which during propagation is constant up to a distance equal to half the distance of the far zone, i.e. to . When the distance between the emitters is increased by more than one wavelength, the spatial distribution of the field takes on a cascade shape. In the first cascade with a length of up to 0.25 of the opening size, the average field amplitude is close to 0.8 of the field amplitude in the middle of the opening. The second cascade with an average field amplitude of about 0.08 is formed at distances from 0.3L to half the distance of the far zone. In sparsed antenna arrays, local bursts of field amplitude up to 0.25 are formed in the near zone outside the spotlight beam. They are located at one distance of the size of the opening and are offset from the axis of the spotlight beam by 0.8 of the size of the opening L.

Conclusions. The spatial distribution of electromagnetic fields near aperture antenna arrays of small electrical dimensions, which is typical for electric or magnetic field sensors in radio measuring equipment, is characterized by uniformly decreasing amplitudes of electric and magnetic fields in both the longitudinal and transverse directions. With large aperture sizes, which is typical for highly directional antennas, this distribution is characterized by the formation of a spotlight beam, which is a weakly inhomogeneous locally plane wave, the average amplitude of which during propagation is constant up to a distance equal to half the distance of the far zone. At distances between emitters greater than one wavelength, the spotlight beam has a cascade shape.