It seems to me that it would be advantageous to design for operation with less than the maximum number of elements. If only 25 of 36 elements need to be used, 11 can fail and be replaced before the link budget degrades significantly. If more than 25 elements are required to get 18 dBic, then it would be advantageous to fly 40-50% more elements than that number.
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: Sunday, April 29, 2007 06:57 UTC Subject: Re: [eagle] Re: Another idea on phased array configuration
So what? We can have, and were planning on having, an 18dB gain array. That doesn't mean we need to turn any elements off.
Matt
John B. Stephensen wrote:
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