Modulation is the process in which a low frequency signal is combined with a high frequency signal. This high frequency signal is called carrier wave and the low frequency signal has some information in it, and it is called messaging signal.
Angle Modulation is a type of modulation in which the phase or the frequency of a carrier wave is varied according to the instantaneous value of the message signal while the amplitude of the carrier is kept constant.
There are two types 3.1 Frequency Angle Modulation: Frequency of the carrier wave varies linearly with the message signal in frequency angle modulation. 3.2 Phase Angle Modulation: The phase of the carrier wave varies linearly with the message signal in phase angle modulation.