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<blockquote data-quote="Waveguide" data-source="post: 859404" data-attributes="member: 364636">If you check the video (in reply #19 in this thread) all the antenna parts are clearly visible.The big reflectors are there but also secondary reflectors and feed-horns. All of these partshave &quot;sidelobes&quot; on their own (unwanted but unavoidable energy spillage).&nbsp;Put these parts on a truck-sized irregular reflecting surface and try to calculate the positionof the sidelobes and nulls 36000 kilometers away.&nbsp;Well, you have to calculate all reflections and diffractions (like ray-tracing) and then integrateamplitude and phase of all the rays to get the total antenna far field pattern. That would be close to impossible and also probably unnecessary. The shape of &quot;the truck&quot; is not well definedif it consists of glued on heat reflectors and metal-coated kapton foil.&nbsp;I've never bought a satellite but most antenna specifications set a fixed upper limit on sidelobelevels and thats it. Where they happen to be or where the nulls are is not an issue. (Unless you buy antennas with steerable nulls to avoid jamming but then you are wearing a uniform have large budget to match.)&nbsp;As a summary - unsymmetrical antennas with a truck-sized reflector on one side and darkspace on the other will not follow any simple design rules.&nbsp;On the other hand it's fairly easy to measure the antenna patterns of an assembled satellite in an anechoic chamber. You can make lots of amplitude/phase measurements over a 2Dsurface and calculate the antenna far field pattern. It's not cheap though, large test chambersare expensive.</blockquote>

[QUOTE="Waveguide, post: 859404, member: 364636"] If you check the video (in reply #19 in this thread) all the antenna parts are clearly visible. The big reflectors are there but also secondary reflectors and feed-horns. All of these parts have "sidelobes" on their own (unwanted but unavoidable energy spillage). Put these parts on a truck-sized irregular reflecting surface and try to calculate the position of the sidelobes and nulls 36000 kilometers away. Well, you have to calculate all reflections and diffractions (like ray-tracing) and then integrate amplitude and phase of all the rays to get the total antenna far field pattern. That would be close to impossible and also probably unnecessary. The shape of "the truck" is not well defined if it consists of glued on heat reflectors and metal-coated kapton foil. I've never bought a satellite but most antenna specifications set a fixed upper limit on sidelobe levels and thats it. Where they happen to be or where the nulls are is not an issue. (Unless you buy antennas with steerable nulls to avoid jamming but then you are wearing a uniform have large budget to match.) As a summary - unsymmetrical antennas with a truck-sized reflector on one side and dark space on the other will not follow any simple design rules. On the other hand it's fairly easy to measure the antenna patterns of an assembled satellite in an anechoic chamber. You can make lots of amplitude/phase measurements over a 2D surface and calculate the antenna far field pattern. It's not cheap though, large test chambers are expensive. [/QUOTE]

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