Grating lobes of an umbrella reflector with cross-catenary tie supports

On the cross-catenary umbrella reflector, the gore surface is supported by a series of tie points anchored to cross-catenaries between ribs. Thus the gore surface, instead of being a wedge-shaped segment of a parabolic cylinder, consists of a large number of rectangular and trapezoidal warped, ruled facets, the corners of which lie on the parent paraboloid of the ribs. The ribs and catenary-supported tie points lie on the parent paraboloid. Surface tension is adjusted to minimize pillowing so that each facet is a quasi-flat warped, ruled surface. The authors have investigated the grating lobes associated with these facets. Because this antenna represents a closer approximation to the parent paraboloid, a smaller decrement of main-beam energy is available for enhanced sidelobes. Results have been generated for a 12-rib, 105-wavelength-diameter reflector. A prominent grating lobe at 9.2 degrees is noticeably above the smooth reflector sidelobe envelope. In this case, the catenary and tie-point spacing are both equal to 6.35 wavelengths and the expected lobes from the authors´ equations have coalesced, yielding an enhanced effect.<>