Hughes Missile Systems Company

General Dynamics Corporation, Electronics Division

General Dynamics Corporation/electronics

John B Gehman

Carter C Smith

Method and arrangement for an airborne radar system particularly adapted to detect large metal targets that are concealed from the air by camouflage or natural foliage. The arrangement includes an antenna that transmits a continuous wave electromagnetic signal having a selectable frequency that preferably has a wave length generally twice the length of an anticipated target and which is carried by a flying vehicle. The frequency of the transmitted signal is chosen to provide maximum penetration of the camouflage or natural foliage and maximum re-radiation from a metal target. Receivers connected to an in-line receiving antenna and to a crossed receiving antenna carried by a flying vehicle detect the radiation that is reflected from the terrain and a target with the same polarization as that transmitted. The co-linear antenna and receiver respond to the reflected radiation while the cross-polarized antenna does not detect this reflected radiation. However, a metal object on the ground re-radiates cross polarized electromagnetic waves in proportion to their angular orientation and lateral distance to the transmitting antenna so that a metal target is detected by observing the output differences for the two receivers.

Airborne metal detecting radar

A bistatic VHF Doppler radar is utilized to detect and track one or more intruders crossing a large annular ring surveilance zone surrounding a central high security installation. A central omni-directional transmitter radiates the surveillance zone with a continuous wave (CW) signal. Predetermined ones of a plurality of receiver antennas circumferentially spaced around the surveillance zone receive a portion of the signal which is reflected by an intruder crossing the surveillance zone and a portion of the signal which is directly radiated from the transmitter antenna. The reflected signal portion may be received by antenna arrays each of which is controlled to form a null in its pattern toward the transmitter antenna to overcome direct signal overload. The direct signal portion may be received by stub antennas. Each antenna array and each stub antenna is connected to a separate channel of a dual channel receiver. An intruder moving across the surveillance zone causes signals representative of Doppler cycles of phase change to be generated. The outputs of the two separate channels are compared and their relative phase changes measured. A detected intruder causes an alarm signal at a central processing station and the Doppler information is processed to generate tracking data which is shown on a display device. An automatic null control circuit may also be utilized to accommodate multipath conditions and static clutter due to environmental factors.

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La Jolla, CA, United States of America

John B Gehman