D. V. Bagno1
1 Moscow Aviation Institute (National Research University) (Moscow, Russia)

1 rw3fo@yandex.ru

Since the phase center of the antenna is determined on each of the two orthogonal polarizations (main and parasitic) separately, the fact of its presence and location depends on the polarization basis. If the antenna has a phase center or a partial phase center for some amplitude and phase distribution, then the electric scanning of the beam by creating flat phase add-on, as well as the shift of the origin of the coordinate system relative to the antenna, do not change the position of the phase center (partial phase center) and are described by theorems on the displacement of the image and the original of the Fourier transform. The existence and location of the phase center or partial phase center of a phased array antenna depends not only on the location of its radiating elements, but also on the amplitude and phase distribution which can vary. Since the excitation of an antenna with a phase center does not necessarily have to be in-phase (or with a linear phase distribution), its amplitude pattern, even expressed as a function of the guiding cosines, may be asymmetric, and the “filled nulls” are not necessarily a sign that the antenna does not have a phase center.

The condition for the existence of a phase center in the strict sense of in-line antennas (including linear arrays) is the Hermitian symmetry of the amplitude and phase distribution, that is, the parity of the amplitude and the odd phase distribution (for example, linear, cubic, etc., in particular, antiphase excitation of the antenna halves) or in-phase excitation. In this case, the partial directional characteristics of the radiation elements (array antenna radiators) should be identical and have uniform phase pattern, that is, the emitters themselves should have phase centers. Antennas with square- and other even errors in phase distribution do not have phase center in the strict sense.

In a flat apertures (flat arrays), the condition is similar – the Hermitian symmetry of the exciting amplitudes and phased relative to the point – the mass center of the amplitude distribution (symmetry of the shape of the aperture and the amplitude distribution and antisymmetry of the phase distribution relative to the point), which is the location of the phase center. A sign of such symmetry is the coincidence of the antenna (its amplitude and phase distributions) with itself or with its complex conjugation when rotating around the center of mass of the amplitude distribution by 180° or as a result of two consecutive reflections relative to any two mutually perpendicular straight lines intersecting at this point.

Distortion of the amplitudes and phases can lead to distortion of the antenna phase pattern and disappearance of the antenna phase center. If the amplitude distribution is asymmetric (but unimodal) or the radiating elements of array antenna are located asymmetrically, but the phase distribution is flat or zero (in-phase excitation), then the antenna has a partial phase center in the direction of the main lobe, it is located in the mass center of the amplitude distribution.

Bagno D.V. Antenna phase pattern analysis and phase center estimation with use of Fourier transform method. Antennas. 2024. № 5. P. 58–73. DOI: https://doi.org/10.18127/j03209601-202405-06 (in Russian)

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