Passbandi

Passbandi (singular passband) is a term used in electronics and signal processing to describe a range of frequencies within which a system’s or component’s response to input signals remains relatively undistorted and above a specified level. In filters and communication channels, the passband is the set of frequencies for which the magnitude of the transfer function is within a defined tolerance of the passband gain, typically within about 3 decibels of the maximum value. Outside this range, signals are increasingly attenuated, creating a stopband.

Passbands are bounded by cutoff frequencies, marking the edges where the response falls outside the acceptable level. The width of the passband is called the bandwidth, calculated as the difference between the upper and lower cutoff frequencies. A passband can be flat or exhibit ripple, depending on the filter type; common classes include low-pass, high-pass, band-pass, and band-stop filters. The center frequency and quality factor (Q) describe how selectively the passband is centered and how narrow or sharp it is.

In practical use, passbands define what frequencies a system transmits with acceptable fidelity. In radio communications, a channel’s passband surrounds a carrier frequency and occupies a finite bandwidth, such as fc ± B/2. In optics, optical filters have transmission passbands corresponding to the wavelengths that pass with high transmission. The exact definition of the passband and the permissible ripple or attenuation can vary with application and design specifications.