Two-Antenna Interference
Peaks and nulls from two antennas trace a family of hyperbolas with the antennas as their shared foci.
Interference pattern of two antennas, with constructive and destructive hyperbolas and their asymptote lines, adjustable antenna spacing.
3λ
Every point on one curve has the same difference of distances to the two antennas. Each curve has its own asymptote angle, sin θ = k/D, so unlike a spacetime diagram there is no single shared "X".