Abstract: An improved microwave radiometric system features the employment of incoherent noise illumination of a selected target for improving the measured radiometric temperature contrast between the target and its spatial background and for increasing the distance at which such a target may be detected. Broad band noise illumination is cyclically transmitted and the receiver is cyclically activated in the high frequency signal comparison system under control of a phase locking loop so that optimum comparison is achieved over a variety of target distances.

Abstract: The multiple beam, short wave planar antenna array system, which simultaneously exhibits low loss, low side lobe levels, high efficiency, and low volume in a design affording independent control of the E and H plane radiation pattern shapes is particularly applicable in microwave radiometric systems such as airborne mapping systems. The antenna system generates symmetrical, matching narrow pencil beam sensitivity patterns by using symmetrically spaced sectorial receiver horns fed energy through a hyperbolic dielectric lens, the horn array and lens residing in a TE.sub.01 mode parallel plate guide, the lens being illuminated by signals collected by a broad wall slotted wave guide array supplied with a thin, planar sheet radome mounted on the energy receiving face of the array.

Abstract: An improved high frequency radiometric system features time shared passive and active modes of operation for correlation of active and passive signal returns. The processed, normalized, and stored passive signals are subtracted from similarly treated active signals to suppress the effect of returns from back ground terrain, thus enhancing true target recognition. A second channel provides discrimination against jamming and spurious signals, thus reducing false alarms.