Bandwidth is limited at all frequencies. This holds true whether we’re discussing those in the kilohertz range used for amplitude-modulated (AM) radio broadcasting; microwaves and millimeter waves for commercial and military radar systems; or those frequencies bands with the shortest-wavelength electromagnetic (EM) signals, including infrared (IR), ultraviolet (UV), x-rays, and gamma rays.
No single component, such as a filter or amplifier, has enough bandwidth to handle them all. But some components are designed for more narrowband use while some are wideband and can process (for example) a number of different communications frequency bands at the same time. It might make economic sense to use a single amplifier or filter rather than two of each to tackle two different frequency bands in a system. But just what are the tradeoffs (other than cost) in using wideband rather than narrowband components in an RF/microwave system?