In radar, a representation of the time-varying amplitude and phase of the received signal as the real and imaginary parts of a time-varying complex number. These parts are called the in-phase and quadrature components and are measured by coherent detection of the received signal. The in-phase signal may be obtained by demodulating the received signal with a local oscillator having the same phase and frequency as the transmitted signal, while the quadrature signal may be obtained by demodulating the received signal with the local oscillator signal advanced or retarded in phase by 90°. See I and Q channels.