WHY CARE ABOUT QUADRATURE SIGNALS?

Quadrature signal formats, also called complex signals, are used in many digital signal processing applications, such as:

• digital communications systems,
• radar systems,
• time difference of arrival processing in radio direction finding schemes,
• coherent pulse measurement systems,
• antenna beamforming applications, and
• single sideband modulators.

These applications fall in the general category known as quadrature processing, and they provide additional processing power through the coherent measurement of the phase of sinusoidal signals.

A quadrature signal is a two-dimensional signal whose value at some instant in time can be specified by a single complex number having two parts: what we call the real part and the imaginary part. (The words real and imaginary, although traditional, are unfortunate because of their meanings in our everyday speech. Communications engineers use the terms in-phase and quadrature phase. More on that later.) Let's review the mathematical notation of these complex numbers.