Method and apparatus for modulating a doppler radar signal

DETAILED DESCRIPTION There is provided by this invention a passive system which does not generate a new radar signal but which continuously varies and reflects the incoming signal and acts to reflect the incoming wave to the source so as to inhibit accurate information gathering concerning the object.
The operation of a doppler-based radar detector is based upon a reflection of electromagnetic waves from an object so that the difference between emanating waves and reflected waves (i.
e.
, the frequency shift) can be detected, correlated and displayed.
It is generally assumed that the frequency shift will occur within certain limits (i.
e.
, the verification window).
Thus, variation in frequency shift, particularly beyond the limits of the verification window, can result in unreliable determinations of speed and thus may not result in any display of data concerning the object.
Similarly, causing the apparatus to oscillate at multiple frequencies of similar amplitude will also inhibit the display of data concerning the object.
Thus in such a system the object may become, in effect, transparent to the radar.
In order to be effective the frequency shift or modulation of the reflected signal should continuously vary beyond predetermined limits with respect to the source so that the source receives different and continuously varying shifts in signals from the reflector.
One way of producing this is by axially oscillating, through the use of a continuously varying signal, a highly reflective member such as a corner cube reflector or Luneberg lens or other highly efficient reflector of microwave energy relative to the incoming signal sufficiently fast to cause a continuous variance in frequency shift which is added to the reflected doppler return signal.
The mechanism for reflector movement must account for numerous factors such as speed, acceleration, stopping, starting, mass, etc.
The inventor believes that doppler-based radar is presently used extensively in civilian applications and thus this invention is believed to be principally applicable in civilian uses