# Radar: FMCW or CW

I purchased a Doppler radar that can run in both CW and FMCW modes. I don't understand how to operate the radar in FMCW mode. I would like to understand what I need to do to get my radar to run in FMCW. I have the spec sheet and it has a VCO with default output of $25\textrm{GHz}$.

Any help would be great. Currently I leave the VCO open as per documentation so that the output Tx is $24\textrm{GHz}$ but is the default operation FMCW?

• Your link is broken... I expect it is this one. – Jan-Bert Sep 20 '17 at 11:39

## 1 Answer

So, look at the block diagram:

The VCO is exactly that – a voltage-controlled oscillator! So the "FM input" needs to be a voltage proportional to the frequency you want to generate. In case of FMCW, you'd probably want to apply an inverted sawtooth to that pin. For characteristics, see the table (green by me):

So for every mV input voltage change, the generated LO changes by -55 kHZ.

As you can see, the receiver path mixes the received signal with a part of the transmit signal – classical radar receiver architecture. Your I and Q contain the difference frequency. You could digitize them simulataneously and use standard radar estimators to get a range/velocity plane :)

• What does the VCO modulation bandwidth here mean? – Hp179 Nov 16 '16 at 13:34