Fully polarimetric differential intensity W-band imager

We present a novel architecture based upon a Dicke-switched heterodyne radiometer architecture employing two identical input sections consisting of horn and orthomode transducer to detect the difference between the horizontal (H) and vertical (V) polarization states of two separate object patches imaged by the radiometer. We have constructed and described previously a fully polarimetric W-band passive millimeter wave imager constructed to study the phenomenology of anomaly detection using polarimetric image exploitation of the Stokes images. The heterodyne radiometer used a PIN diode switch between the input millimeter wave energy and that of a reference load in order to eliminate the effects of component drifts and to reduce the effects of 1/f noise. The differential approach differs from our previous work by comparing H and V polarization states detected by each of two input horns instead of a reference load to form signals ΔH and ΔV from adjacent paired object patches. This novel imaging approach reduces common mode noise and enhances detection of small changes between the H and V polarization states of two object patches, now given as difference terms of the fully polarimetric radiometer. We present the theory of operation, initial proof of concept experimental results, and extension of the differential radiometer to a system with a binocular fore optics that allow adjustment of the convergence or shear of the object patches as viewed by the differential polarimetric imager.