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An interfering signal usually reaches the interfered antenna from an off bore sight direction, both in azimuth and elevation. The common methodology is to estimate the intercardinal gain G(φ,θ) as a linear combination of the cardinal patterns G(φ) and G(θ). This paper proposes a new approach based on geometrical reasoning, looking for the locus in space of pairs of angles φ and θ, having an iso-gain. The hypothesis is that these loci are ellipses drawn on a sphere. Equations for equivalent angles, φ' or θ' are derived. G(φ,θ) is found using the G(φ) or G(θ) pattern, at the equivalent angle. Finally, the hypothesis is compared to a numerical calculation and a good match is found.