FMCW radar parameters

[adnan012]

I want to ask few questions regarding FMCW radar

For a radar of 10-200 meter range (resolution 10 or 20 meter) how following parameters are selected

Frequency band (HF, VHF or Microwave)
Bandwidth (Fmin -- Fmax)
Sweep rate
Sample rate required for ADC

Best Regards

 

[vfone]

In FMCW radar the distance to the target (range R in meters) and the range resolution are not function of frequency:
R=(2*t)/2 t is the propagation time (round-trip time in seconds).

Range resolution Rres in meters is only function of bandwidth B (fmin--fmax, in Hz):
B=c/(2*Rres) c is speed of light and Rres is the range resolution
For range resolution of 10m the bandwidth B=15MHz.

Sweep rate (or chirp duration Tch in seconds) is:
Tch=(2*R*B)/(c*fb) fb is the beat frequency in Hz

ADC sample rate is:
Fs=(B*2*R)/(Tch*c)

 

[volker@muehlhaus]

Bandwith is an issue, as vfone already discussed. At microwave frequencies you will find unlicensed (free) frequency ranges offering enough bandwidth to operate FMCW with reasonable bandwidth.

You also want to have control over beam direction/beam width. That is possible at microwave frequencies with relatively small antennas.

 

[adnan012]

Thanks for reply.

c = 3000,00000

1) R=(2*t) For 500 feet its 1000nS
2) B=c/(2*Rres) = (300000000)/(2*10) = 15MHz
3) Tch=(2*R*B)/(c*fb) = (2*10*15,000,000)/(300000000*20000) = 0.0005s
4) Fs=(B*2*R)/(Tch*c) = (15,000.000*2*10)/(0.0005*300000000) = 20000 (Hz)

Please correct me if there is miscalculation.

Regards!

 

[tony_lth]

I just made an example, pls comment if I am wrong:
R=12.8m
t=2*R/c=85.33ns
Rres=0.05m
B=c/(2*Rres)=3GHz
Fs=6.25Msps=(B*2*R)/(Tch*C)==》Tch=40.96us
Tch=(2*R*B)/(c*fb)==>fb=6.25MSPS

 

[vfone]

Tony, your calculations are good. Usually fb is in Hz because is in frequency domain.

adnan012, sorry is a typo on my previous post: R=(c*t)/2 and t=(2*R)/c
Follow the example that Tony posted and you will be just fine.
From his example you see that have to know (or to define) few things as: Range resolution (Rres), ADC sampling rate (Fs).
Or, if you don't know these parameters, have to define the beat frequency (fb) or the chirp duration (Tch).