E.V. Volkhonskaya – Dr.Sc.(Eng.), Associate Professor

E.V. Korotey – Post-graduate Student

A.V. Skrzydlewski – Ph.D.(Eng.)

There is a trend of new super high frequency ranges development in satellite navigation, communication and surveillance systems. Two-mirror Cassegrain and Gregory antennas are used in the earth segment of such systems. The directional properties of these antennas depend on their geometrical parameters and must be agreed upon the strict requirements. The analysis of numerous geometrical parameters and directional properties of two-mirror Cassegrain and Gregory antennas showed the need for structure optimization with the aim of effective radiation parameters getting. The aperture method is commonly used for directional properties calculation, but it has the least accuracy among the known methods. Its use leads to overvaluation in the maximum side-lobe level, directivity and reflector efficiency and also undervaluation in the beam pattern width. Using of a more accurate surface currents method allows you to normalize these directional properties estimates.

The results of mathematical modeling of Gregory two-mirror antenna radiation field within surface currents method are represented in this work. Authors on the basis of standard approach in calculation of currents on the conductive surface, induced by the wave, on the one side and within results of analysis of two-mirror antenna geometrical parameters on the other side have received analytical expressions, which allows determine antenna radiation field. Structure optimization of second reflector was produced with aim of direct properties achievement, which compliant to antenna of satellite communication system earth segment requirements. It was shown that the product of aperture efficiency and reflector irradiation efficiency can be used as an objective function in structure optimization. Its maximum value determines the optimal value of the considered structural parameter. The radius of second reflector aperture, its focal length and depth, and a distance between the irradiator and the top of the second reflector were used as optimized parameters. The results of frequency dependences of radiation parameters investigation show that the beam pattern width less than the maximum allowable value by 4,7−6,5%, maximum side-lobe level less than the maximum permissible value by 6,1−6,8 dB, directivity greater than the minimum allowable value by 2,5 dBi, reflector irradiation efficiency exceeds expected values of 0,7−0,85 by at least 5,9−7,2%. Developed model may be used for structure optimization procedure at the design stage of the Gregory two-mirror antenna.

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