1. Filter concept

The best-known filter extracts the components of a complex signal within a certain frequency range. This is known as an attenuation filter. Outside a particular frequency range, the amplitude of the signal is greatly attenuated.

A filter can also modify only the phase response of a signal. This is known as a phase-correcting filter.

Filtering is applied to signals represented in analog form (analog filters), or in digital form after signal sampling (digital filters). The former act directly on the analog input signal and are made up of a set of analog components (resistors, capacitors, inductors, active elements, resonators, etc.), while the latter require prior digitization of the input signal and are made up of a set of digital operators (multipliers, adders, delays, etc.).

Filters apply to telecommunication systems...