Category: Software
Product Number: CN0565
Software Version: Phaser Radar Examples
Jon,
First, thanks very much for posting video 7 in your Build Your Own Radar series. It's great! Adding the MTI information is awesome and super helpful. Also, thanks for the shout out in pointing you in the direction of the X-band horn antenna. These seem to work quite well. The MTI processing looks like it works really well! I haven't had a chance to do field testing with it myself yet but look forward to the improvement.
In looking through your Range_Doppler_Plot.py example I noticed you tweaked some of the key radar parameters since video 6. Specifically you sped up the ramp time from 500 us to 300 us and lowered the Pluto's sample rate a bit from 5 Msps to 4 Msps. My first question was what prompted you to make these tweaks?
My second question has to do with finding the Phaser's FMCW max unambiguous range given these new parameters. I used the new parameters from your Range_Radar_Plot.py:
c = 3e8
sample_rate = 4e6
chirp_BW = 500e6
ramp_time = 300 us
And then calculated the maximum range, Rmax using what I believe to be the correct calculation:
Rmax = (fmax *c) / (2 * ramp_slope) (equation A)
where:
fmax = sample_rate / 2 = 2e6 (to meet Nyquist max measurable bandwidth frequency using the Pluto)
ramp_slope = chirp_BW / ramp_time = 1.667e12
which gives the max range (I believe) of:
Rmax = ( 2e6 * 3e8) / (2 * 1.667e12) = 180 meters
Does this seem correct? And now to the real question that's bugging me. Many references I find that include the FMCW max range equation will have the sample rate in place of the fmax and are written in some form like this:
Rmax = (sample_rate * c) / (2 * ramp_slope) (equation B)
which would give twice the max range, 360 meters in this case. Is the max range equation properly of the form of equation A or equation B (or something else entirely)?
Surprisingly, I couldn't find a clear reference to this is Charvat's book nor in the MIT Lincoln Lab lectures. Here are some other references to FMCW max range it I've found in searching around that only served to confuse this seemingly simple issue:
There are many others however none clear up this confusion between using sample rate and frequency. Can you you guys help clear this up?
Thanks very much,
Robert
