A method for compensating a reference signal used in a coherent receiver of a micro-doppler sensor having a transmitter includes the steps for: (a) repeatedly measuring phase differences between a signal emitted by the transmitter a first time and a previous signal emitted at a previous time so as to produce a plurality of phase error signals; (b) accumulating the phase error signals over a propagation time between the transmitter and the coherent receiver so as to produce a cumulative phase error signal; and (c) modulating a signal produced by the transmitter at the end of the propagation period so as to generate a compensated reference signal having a phase characteristic substantially identical to the signal produced by the transmitter at the beginning of the propagation period. A phase error or noise compensator, which can form part of a micro-doppler ladar system, is also described.

Optical techniques are disclosed for improving the range resolution of a radar system. An optical source produces chirped optical pulses whose frequency changes linearly with time, wherein the pulse duration is close to the repetition period (quasi cw radiation). The optical source illuminates the target that scatters a portion of the light back into collecting optics of the ladar's receiver. The delayed back-scattered optical waveform is mixed optically with a reference waveform in a non-linear medium to produce optical radiation at a new frequency. The spectral properties of the non-linearly generated light contains information about the distance to the target. Different approaches that may be chosen for non-linear optical mixing are disclosed including sum and difference frequency generation in non-linear crystals.

A power measurement circuit, suitable for use in communications devices, is provided in which first and second signals derived from the signal of interest are passed through a multiplier, and the output of the multiplier is passed through a filter. In one embodiment, the filter provides a signal substantially representative of or relating to the DC component of the signal output from the multiplier. In another embodiment, the filter provides a signal substantially representative of or relating to the average power of the signal of interest. Advantageously, in one embodiment, the signal output from the filter bears a substantially linear relationship to the average power of the signal of interest over a desired region of operation. In a second embodiment, the signal output from the filter is advantageously substantially frequency invariant over a desired region of operation.

A power measurement circuit, suitable for use in communications devices, is provided in which first and second signals derived from the signal of interest are passed through a multiplier, and the output of the multiplier is passed through a filter. In one embodiment, the filter provides a signal substantially representative of or relating to the DC component of the signal output from the multiplier. In another embodiment, the filter provides a signal substantially representative of or relating to the average power of the signal of interest. Advantageously, in one embodiment, the signal output from the filter bears a substantially linear relationship to the average power of the signal of interest over a desired region of operation. In a second embodiment, the signal output from the filter is advantageously substantially frequency invariant over a desired region of operation.

A laser transmitter is amplitude modulated with a chirp signal to illumin an entire scene or field of view. A mixing process occurs in the received light path using an electro-optic light modulator positioned just in front of the focal plane detector array. The detector array detects and integrates the mixed light signal over some field of view. Numerous image frames are recorded periodically in the time over the FM period. The Fourier transform taken over time for a pixel establishes the range to the target in that pixel. Performing the Fourier transform for all pixels yields a three-dimensional image of objects in the field of view. Such an arrangement yields a scannerless ladar possessing high range resolution with no range ambiguities.