Zone plate reflector antennas for applications in space

The zone plate (ZP) reflector antenna is presented as a low cost, low weight alternative to parabolic reflector and array antennas on satellites and interplanetary spacecraft when antennas with high gain and low sidelobes are required. The reflector efficiency of a zone plate antenna with four phase segments in each Bone is 95 percent. The directional patterns of zone plate antennas were computed by recursive integration of the circular aperture Fresnel integral. Computed antenna patterns are similar to the pattern of a uniformly illuminated parabolic reflector. The ZP reflector has 4 to 5 percent larger beamwidth than the same diameter parabolic reflector, and the first sidelobe level approaches -17.7 dB as the number of zones increases. Peak sidelobe levels decrease monotonically. The beamwidth increases and peak sidelobe levels decrease as edge illumination decreases. Chromatic aberration limits the instantaneous bandwidth of a zone plate antenna, but the antenna can be tuned over broad frequency bands by moving the feed position. Aberration limited scan angles are larger than obtainable with parabolic reflectors but, for a given scan angle, the maximum frequency for aberration free beam forming reduces with plate diameter and increases with the F-number. Achievement of large scan angles at K-band and higher frequencies requires corrective optics. Zone plate antennas can be used in a variety of applications where low cost, low weight, multiple beam or scanning of a narrow beam over a large angular field are required