The radar system that I'm working with contains a linear FMCW S-band (2.26-2.59 GHz) signal with a bandwidth of 330MHz and a pulse duration of 20ms. Also, the received signal is dechirped.
Thanks for your comments and suggestions in advance.
I assume you mean that the FMCW sweep repetition rate is 20ms. At first glance, this sets the FFT bin separation to 50 Hz if you frame the sample set around a single sweep period. This gives a range resolution of about 45cm based on your frequency sweep parameters. The number of bins is set by the extent of the range that you wish to resolve (and by definition, the bandwidth of the dechirped signal). Hence, let's say your dechirped signal bandwidth is 10kHz. You will need at least 2 times this to satisfy the Nyquist sampling criterion, or 400 samples (or 512, if using the usual power-of-2 FFT algorithm).
Of course this will depend somewhat on the shape of your frequency sweep and/or if you are using data over several sweeps.
Thank you so much George Slade for your clear answer.
Yes, the right expression is the Sweep repetition rate or interval as you mentioned. :)
So as you said the appropriate sampling rate is related to the dechirped bandwidth, which is related to the range extent (or maximum range). Do you know how to estimate the range extent?
For example, if I configure the system for a near-field (about 10m) the dechirped bandwidth would be 1.1KHz and the sampling-rate should be 2.2KHz. That means 44 range samples?
Thanks again.
Best regards,
At least 44 samples. Given the power of DSPs these days, be safe and go for significant oversampling.
The useful range will depend on the transmit signal strength (Tx EIRP - includes antenna gain), the target radar cross-section and the receiver sensitivity (noise figure, LO phase noise, etc, Rx antenna gain). Google "radar range equation" and have a read. For good detection, you will need about 10dB received signal to noise ratio or more in the return signal. Use the radar range equation to estimate this and base your receiver bandwidth accordingly. Consider using a range amplitude correcting highpass filter (f^2 slope to correct for amplitude reduction for far-away targets) as well.
Cheers and have fun
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