A bifocal reflector antenna with Gregorian configuration

The bifocal dual reflector antenna system is an important wide-angle scanning antenna configuration, offering an extra degree of design freedom over single reflectors. Although bifocal subreflectors tend to be large, offset configurations can be designed to minimize this effect. The article examines a relatively unknown bifocal configuration, one having a concave, Gregorian subreflector. Also, design formulas for all types of bifocal systems are presented, which extend the exact, two-dimensional main and subreflector profile curves into 3-D reflector surfaces. A design example for a symmetric Gregorian bifocal with a 20/spl deg/ field of view (/spl plusmn/8/spl deg/ design scan angle) is given.