At 04:14 PM 12/3/2002 -0800, Tim May wrote:
Parabolas are most desired when a broad range of frequencies are simultaneously being received and need to be brought into a common crisp focus (e.g., handling chromatic aberration in optical telescopes). Secondaries and corrector plates, as are common to handle field flattening, were considered too complex for the application. At these frequencies and reflector size the difference of figure between a parabola and a sphere is relatively small though not insignificant. I believe the engineers were able to introduce balloon distortions approaching a parabolic figure. In the end the engineers found other imperfections of the antenna and feed predominated.On Tuesday, December 3, 2002, at 11:09 AM, Steve Schear wrote:In the late 70s, I was at TRW we built inflatable (beach ball) antennas for a black project. About 1/3 of the balloon's inside surface was aluminized and the feed was simply snapped into place at the opposite side. The antenna could either be used hand-held or place in a ring mount on a flat surface. This sort of approach could work well for cell phones and WiFi cards with external antenna port.
For cell phones the entire instrument could be placed in at the reflector's focus and operated via a mic/headset adapter (some older Nokia models have an external antenna port behind a small rubber plug on the rear.)
Clever, but a section of a sphere is not a section of a paraboloid, so how did you deal with the focus issues?
Perhaps the feed part had a secondary antenna (like a secondary mirror in a telescope to correct aberrations in the larger primary).
steve
