[eagle] Re: Another idea on phased array configuration
John B. Stephensen
kd6ozh at comcast.net
Sat Apr 28 23:57:30 PDT 2007
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.
----- Original Message -----
From: "John B. Stephensen" <kd6ozh at comcast.net>
To: "Matt Ettus" <matt at ettus.com>
Cc: "AMSAT Eagle" <Eagle at amsat.org>; <K3IO at verizon.net>; "Louis McFadin"
<w5did at 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
> 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
> ----- Original Message -----
> From: "Matt Ettus" <matt at ettus.com>
> To: "John B. Stephensen" <kd6ozh at comcast.net>
> Cc: "Louis McFadin" <w5did at amsat.org>; "Robert McGwier"
> <rwmcgwier at gmail.com>; "AMSAT Eagle" <Eagle at amsat.org>; <K3IO at 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
>>> 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?
> Via the Eagle mailing list courtesy of AMSAT-NA
> Eagle at amsat.org
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