Doppler radar system

Claim 1

AN AIRBORNE DOPPLER RADAR SYSTEM WHEREIN THE CENTROID OF THE SPECTRUM OF FREQUENCIES REFLECTED BACK REMAINS CONSTANT REGARDLESS OF CHANGES IN THE REFLECTIVE CHARACTERISTICS OF THE TERRAIN BENEATH AN AIRCRAFT, COMPRISING: (A) MEANS FOR PROPAGATING AN ELLIPTICAL BEAM OF ELECTROMAGNETIC ENERGY DOWNWARDLY FROM THE AIRCRAFT TO ILLUMINATE AN AREA ON THE TERRAIN, SUCH AREA: (1) LYING BETWEEN THE GROUND TRACK OF THE AIRCRAFT AND A FIRST LINE PERPENDICULAR THERETO; (2) BEING SYMMETRIC ABOUT A SECOND LINE LYING BETWEEN A THIRD LINE PERPENDICULAR TO THE HORIZONTAL PROJECTION OF THE LONGITUDINAL AXIS OF THE BEAM AND FOURTH LINE PASSING THROUGH THE CENTER OF SUCH AREA AND DEFINING POINTS FROM WHICH RETURNS OF A SINGLE FREQUENCY ARE REFLECTED; AND, (3) HAVING A LENGTH TO WIDTH RATION, WHERE THE LENGTH IS MEASURED ALONG THE SECOND LINE AND THE WIDTH IS MEASURED ALONG A FIFTH LINE PERPENDICULAR TO THE SECOND LINE, BETWEEN THE LIMITS OF 2:1 AND 10:1; AND, (B) MEANS FOR PROCESSING THE ELECTROMAGNETIC ENERGY REFLECTED BACK TO THE AIRCRAFT FROM SUCH AREA TO DERIVE A SIGNAL INDICATIVE OF THE GROUND SPEED OF THE AIRCRAFT.