The length of each side of a rectangular broaside array with a given directivity is sqrt(directivity/12.6). For a 17.5 dBi gain this works out to sqrt(56/12.6) = 2.1 wavelegths. A perfect 16-element array with 0.5-wavelength spacing would be slighty too small. However, a lossy 25-element array should provide sufficient gain. 9 elements of a 36-element array or 14 elements of a 41-element array could be held in reserve.
73,
John KD6OZH
----- Original Message ----- From: "John B. Stephensen" kd6ozh@comcast.net To: "Matt Ettus" matt@ettus.com Cc: "AMSAT Eagle" Eagle@amsat.org; K3IO@verizon.net; "Louis McFadin" w5did@amsat.org Sent: Sunday, April 29, 2007 06:21 UTC Subject: [eagle] Re: Another idea on phased array configuration
The spreadsheet distributed early last year shows a 9 degree squint angle at the leading and trailing horizons at apogee. An antenna with an 18 degree half-power beamwidth has a gain of 41000/(HPBW^2) = 127 = 21 dBi. It would be best to illuminate the earth with a loss of only 1 dB at the edges and the -1 dB beamwidth is going to be 2/3 or less of the -3 dB beamwidth. The gain should then be adjusted by 4/9 or 3.5 dB less. This would be 17.5 dBi.
73,
John KD6OZH
----- Original Message ----- From: "Matt Ettus" matt@ettus.com To: "John B. Stephensen" kd6ozh@comcast.net Cc: "Louis McFadin" w5did@amsat.org; "Robert McGwier" rwmcgwier@gmail.com; "AMSAT Eagle" Eagle@amsat.org; K3IO@verizon.net Sent: Saturday, April 28, 2007 19:57 UTC Subject: Re: [eagle] Re: Another idea on phased array configuration
John B. Stephensen wrote:
Since the generated beam needs to cover the entire earth from a maxmum of 35,000 km in alttude, the beam can't be made very narrow. I don't think that all 36 or 43 elements ever need to be on at one time. Many could be held in reserve.
Where do you come up with this? What sort of analysis?
Matt
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