Why must radio telescope surfaces be more precise for shorter wavelengths?

Radio telescope surfaces must be manufactured with higher precision for shorter wavelengths because departures from a perfect parabolic shape become significant when they reach a few percent or more of the operating wavelength.1

If the reflecting surface is not sufficiently accurate, it cannot effectively focus the incoming radiation, leading to a loss of signal quality and performance. Consequently, while telescopes designed for longer metre wavelengths can function with relatively simple surfaces—such as wire fencing—those intended for millimetre or submillimetre observations require highly precise, rigid surfaces to maintain their focus. To achieve this, modern telescopes often utilize computer-controlled actuators to adjust surface panels to within a few tenths of a millimetre, ensuring the antenna remains accurate enough to detect these shorter, more sensitive signals.12