For a rectangular aperture of a*b the first null in E-plane occur at _______
(a) sin^-1(λ/b)
(b) sec^-1(λ/b)
(c) cos^-1(λ/a)
(d) sin^-1(λ/a)
The question was asked in an interview.
Origin of the question is Aperture Antenna topic in division Aperture Antenna of Antennas