In the two divergence angle equations, one uses frequency with diameter and the other uses wavelength with diameter.

• A. True
• B. False
• C. Only frequency is used
• D. Only wavelength is used

Answer: (A)

Diffractive (divergence) spreading is governed by how large the wave’s wavelength is relative to the aperture diameter. For a circular aperture, the main lobe angle is proportional to λ/D (often written as θ ≈ 1.22 λ/D for the first null). Since wavelength and frequency are linked by λ = c/f, you can also express the same relationship in terms of frequency: θ ≈ 1.22 c/(f D). So you end up with two common forms that describe the same physical spreading: one uses wavelength with diameter, the other uses frequency with diameter. This is why the statement is true. If the propagation medium changes, the wavelength in that medium changes while frequency stays the same, but you can still convert between forms using λ = c/nf when applicable.