Finding a parabolic dish with a suitable surface for Millimeter band work is not an easy matter. Size and surface accuracy become very important factors in its selection. The larger the dish the higher the gain and the more critical its aiming. This becomes very apparent at 47 Ghz and even more so at 78 Ghz. At 78 Ghz the gain of a 1-foot dish is～45 dB and the resulting beam width at the 3-dB points is s mere 0.93 degrees. A dish useable for these frequencies can be found in the Edmund's Optics catalog. There are three sizes available - 12, 18 and 24 inch. I chose to use the 12 inch model for ease of handling, mounting anc aiming. It's stock number is T53-875 and sells for $39.60. The parabolic surface accuracy is excellent Aim the dish at the sun, hold your finger at the focal point (3 inches), and be prepared for pain! The dish is spun from .040 inch aluminum and has a rolled lip around the outer edge. There is a 3/4 inch hole in the center and the surface is basically a parabolic mirror.
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