Chirp

A chirp is a signal in which the frequency increases ('up-chirp') or decreases ('down-chirp') with time. It is commonly used in sonar and radar, but has other applications, such as in spread spectrum. In spread spectrum usage, SAW [?] devices such as RACs are often used to generate and demodulate the chirped signals.

In a linear chirp, the frequency varies linearly with time:
f(t) = f₀ + f×k×t
This type is easy to generate.

In a geometric chirp, the period of the signal varies linearly with time. Although harder to generate, this type does not suffer from reduction in correlation gain if Doppler shifted by a moving target.