Radar Search Antennas and RFI

The susceptibility of radar search antennas to radio-frequency interference (RFI) is determined to a great extent by the minor lobe structure. The use of detailed, three-dimensional patterns to predict RFI is not practical because the fine structure of the antenna pattern changes with frequency, range in the Fresnel zone, and site effects. Statistical gain studies have shown that the characteristics of individual antennas and the mutual gain characteristics of two Interfering antennas can be described with Gaussian curves. The statistical description Is Independent of in-band frequency variations and range changes (including Fresnel zone), but site effects cause small changes in the median gain.