Two A/D use cases for Radar

[senmeis]

Hi,

I have two questions to this document: http://ece.wpi.edu/radarcourse/Rada... Parameter Estimation and Tracking Part 1.pdf.



1. On page 9: Estimation of the range of a target is based upon using A/D sampled measurements of the round trip time to and from the target.

As far as I understand it means the number of A/D clock cycles can be used to determine the range. Is it correct?

2: On page 15: This calibration process is usually accomplished by launching a balloon with a sphere (RCS independent of orientation) attached by a lengthy tether and measuring the amplitude in A/D counts and the range of the balloon.

Can anyone explain why ADC counts are related to RCS?

 

[marcusl]

1. Yes, counting ADC clock cycles is equivalent to measuring time. Keep in mind that many pulse waveforms exhibit range-Doppler coupling, so a target's motion can change its apparent range. This is universally taught in radar courses, so I'm sure that is covered in a different part of your tutorial.
2. It is necessary to calibrate the overall amplitude response of the radar, which involves both the transmitted power and receive gain (both include the antenna gain). Amplitude is volts = ADC counts. The operational value of interest to a radar operator is RCS, because that relates to the target's size (more or less, anyway. Stealth aircraft can be large but have a low RCS.) A target such as a sphere that has a known, analytically calculated RCS is sufficient for radar amplitude calibration.