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Let me describe the Vivaldi-like Quad-ridge feed we are using in a VLBI
project; it is made by ETH-Lindgren (<a
href="http://www.ets-lindgren.com/page/?i=3164-05">http://www.ets-lindgren.com/page/?i=3164-05</a>)
and is described in a paper at <a
href="http://www.mwjournal.com/Journal/article.asp?HH_ID=AR_601">http://www.mwjournal.com/Journal/article.asp?HH_ID=AR_601</a>.
In our case, we are using it in radio astronomy application where
losses are critical (mainly to minimize system temperatures). We are
using it in the 2-15 GHz range and the feed and LNAs are cooled to ~20
K. We are achieving a Tsys of < 40K over the entire range. The basic
commercial feed looks like this<br>
<blockquote type="cite"><img
src="cid:part1.08090002.05010903@verizon.net" border="0" height="209"
width="430"></blockquote>
The red material on the outside is plastic and only serves as a
mechanical support. The blades are ~3/16" thick aluminum. At the base
of the feed is a balun.<br>
<br>
In our application, it looks something like this:<br>
<blockquote type="cite"><img
src="cid:part2.00090108.02050906@verizon.net" border="0" height="357"
width="399"></blockquote>
<br>
Note that this feed IS NOT MADE OF PCB MATERIAL because we do
everything possible to minimize losses. For the ACP, despite the
literature Bob posted, IMHO even Duroid will have unacceptable losses,
hurting both the uplink TX gain (and perhaps burning up with TX power!)
and both the downlink gain AND Tsys. <br>
<br>
In case you are curious about the LNAs we are using, they are similar
to this design, which is use on Berkeley's 42 antenna (84 LNAs in the 2
polarizations) Allen Telescope Array (ATA) in northern CA near Mt
Shasta (if it doesn't get burned down). The look like this:<br>
<blockquote type="cite"><img
src="cid:part3.02050601.02080302@verizon.net" border="0" height="525"
width="770"></blockquote>
73, Tom<br>
<br>
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