Quadrature phase
From Wikipedia, the free encyclopedia
Communication signals often have the form:
![A(t)\cdot \cos[\omega t + \phi(t)] \equiv I(t)\cdot \cos(\omega t) - Q(t)\cdot \sin(\omega t)\,](../../../math/0/7/e/07e03da349214d0db9e289241f6fb13e.png)
where 
represents a carrier frequency, and:
![I(t) = A(t)\cdot \cos[\phi(t)]](../../../math/1/c/3/1c34df7bf2df4f2f28fdab7118ed2dcf.png)
![Q(t) = A(t)\cdot \sin[\phi(t)]](../../../math/c/b/0/cb0734174f7d31bfc8fa854a38263623.png)
and 
represent possible modulation of a pure carrier wave: 
. The modulation alters the original 
component of the carrier, and creates a [new] 
component, as shown above. The component that is in phase with the original carrier is referred to as the in-phase component. The other component, which is always 90° (
radians) out of phase, is referred to as the quadrature component.
