Re: passive radar theory refrence needed

Peter Divos wrote:
Hi,

I heard there are some types of radar which operate passively, this
means, they dont send any signal and dont wait for the echo, but they
get some random electromagnetic waves from the air which are reflected
on objects as well and it is possible get some image in exchange of
some computation.

There are two different methods which sort of fit your description:

1) Radiometry

This uses thermal noise emissions/reflections from objects to form an image. The basic idea is very similar to an optical image, except that the wavelengths of the incoming radiation are much longer. With this method you cannot get range or Doppler information directly. Typically you would scan the area to be imaged using a very high gain (narrow beam) antenna and record received power to form an image.

2) Passive radar

This makes use of an existing transmitter, e.g. a television transmitter, and looks for reflections of the signal from the existing transmitter. You could, for example, point one antenna at a TV transmitter and one at the target. You could then compare the direct and reflected signals to get the relative time delay and Doppler shift. you can then calculate the total path difference (distance from transmitter to target + target to receiver - transmitter to receiver) and it's rate of change.



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