Why do we use I/Q signals in radar technology? Here you find a simple explanation.

Two signals where the phase is 90 degrees apart are called "in quadrature". Cosine wave and a sine wave are quadrature wave forms.

IQ signal

The amplitude of the cosine wave we is called I or the In-phase signal.

The amplitude of the quadrature waveform or the sine waveform is Q.

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By appropriately varying the I and the Q as a function of time, we can generate the resulting sum of those wave forms as

  • frequency modulation,
  • or phase modulation.

Through simple amplitude modulation of I and Q, we can create complex modulation in the resulting sum.

That's really the whole thing about IQ modulation and IQ signals. This is why they're really used in modern software-defined radio and a lot of other applications.


All this works in the opposite direction just as well for demodulating signals.

Essentially if you take any RF signal and then demodulate it with quadrature local oscillators to create the I and Q data streams, there is enough information in the I and Q to fully demodulate that signal whether you're doing it for receiving the signal that to listen to it or to grab data out of it or to analyze the signal.

Once you've got a signal represented by its I and Q components, you know everything there is to know about that signal.

This is the basis for most software-defined radios, because all these IQ signals can easily be generated or analyzed in software and processed through ADCs and DACs and things like that for a lot of common low cost software-defined radios.

In radar, we can use complex modulation in transmitter for waveform generation using I/Q signals. In the radar receiver, matched filters for pulse compression can be applied on demodulated I/Q signals. Also, the Doppler information of the target can be retrieved from complex data from demodulated I/Q signals.

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