fmcw radar sampling requirements I have been reading about "all-digital" or "software-defined radars". Lately, I was trying to simulate an FMCW short range radar in Matlab. One thing that struck me during the simulation is that to achieve a range resolution of around a 100 cm or less, the signal bandwidth is quite large -- in multiple GHz. This means, if one wishes to realise a digital implementation, one needs a really high speed ADC - multiple GigaSamples/second. Such ADCs are either not available and if you find something towards the top end of the high speed ADCs out there, the processing requirements are going to be ridiculously high. And of course, if you are clocking your baseband processor in GigaHertz, the power requirements of the device (typically an FPGA) are again going to be impractical.

My questions:


How, if at all, high-resolution, high-bandwidth digital radars are realised in practice?
what would make sense in case of FMCW radar is to mix the transmitted signal and the target return signal and digitize only the beat frequency for Inverse FFT and further analysis. In that case, could you still call it a digital or software defined radar?
A quick scribble on paper shows that FMCW radar has a resolution of 

$$
\Delta d = \frac{c}{2b}
$$ with $c$ being the speed of wave propagation (aka speed of light, essentially), $b$ being the bandwidth, and $2$ coming into play because the wave has to trave both ways. For your $\Delta d\overset != 1\mathrm m$, 

$$
1\mathrm{m} = \frac{3 \cdot 10^8 \frac{\mathrm{m}}{\mathrm{s}}}{2b}
$$ 

which means you'd only need $b\ge 150\, \mathrm{MHz}$ in my calculation.

That's something that software defined radio devices can do nowadays.

Hence, to answer your questions:
My questions:


  How, if at all, high-resolution, high-bandwidth digital radars are realised in practice?


Simply be mixing the signal down to baseband (or a low IF), and then sampling it with an ADC.


  what would make sense in case of FMCW radar is to mix the transmitted signal and the target return signal and digitize only the beat frequency for Inverse FFT and further analysis.


Yes, that's the way it's done in most "small" FMCW radars, for example automotive radars.


  In that case, could you still call it a digital or software defined radar?


Puh. Digital: yes.
Software defined: well, if everyone asked me, no, but paper doesn't blush, so there's probably someone out there who calls this kind of radar "software defined". Please don't do that.