V.I. Andrianov, K.V. Kozlov, A.P. Kurochkin, M.A. Tsvetkova

The feature of the shareborne SAR active phased array antennas (APAA) is relatively small sector of the scanning angle. It makes possible to dispose radiating elements with the gap of several wavelengths as in the sparse antenna array. Using the sparse antenna array leads to the significant reduction of active modules amount in APAA, to reduction of the mass, cost and power consumptions, that is very important for spaceborne apparatus. The sparse antenna array has as known the interferential side lobes in their radiation pattern. The method for the interferential side lobes level reduction in sparse arrays, is suggested and researched. According to this method the antenna array is sparse only in a horizontal plane and has unequal gaps in the different strings and equal gaps along each string. The gap between radiating elements changes from string to string according to the particular rule. Each string forms the interferential side lobe with its individual direction relative of the aperture normal direction. As a result the interferential side lobe of antenna array reduces. The efficiency of this method was tested on APAA with the next characteristics: the center frequency f0 = 3,2 GHz, the scanning sector in vertical plane is ±17,5º, the scanning sector in horizontal plane is ±7º, the side lobe level is -20 dB, sizes of aperture are 10×3,6 m. The mathematic modeling of the array factor showed that for reducing of the interferential side lobe level to -20 dB it is enough to use 17 strings with the linear difference in 0,012 m between the neighbour strings. The amount of radiating elements and coupled with them active modules is 1164, that is more than in five time smaller relative to the non-sparse antenna array of a such dimension.