For those interested in building horn antennas, take a look at
The W1GHZ Online Microwave Antenna Book
http://www.w1ghz.org/antbook/contents.htm
by Paul Wade, W1GHz (ex N1BWT). Chapter 2 of this free book
http://www.w1ghz.org/antbook/chap2.pdf
is on horn antennas. Paul has written a program, called HDL_ANT which used the approximate dimensions from a set of tables by Cozzens to design pyramidal horn antennas with gains from 10 to 25 dB. The nice thing about this program is that it can create a postscript file which gives the layout on paper, so you cut the paper, put the folds where it shows, and you have your horn. But it wont run under 64-bit Windows 7, but it does work under 32-bit XP. There is a link to both the binary and source code of HDL_ANT at the "Software" section at the bottom of
http://www.w1ghz.org/antbook/contents.htm
Paul gives the reference for the tables
D.E. Cozzens, "Tables Ease Horn Design," Microwaves, March 1966, pp. 37-39.
If you use Paul's program to generate a postscript file, you can print it using
http://www.lerup.com/printfile/ I would check the dimensions with a ruler, since your printer might not give an exact 1:1 reproduction. I found using that utility worked 100% from the postcript file on my Xero postscript printer. But if I printed the PDF at
http://www.w1ghz.org/antbook/chap2.pdf
then the scaling was in error by about 5%. If you don't have a true postscript printer, then
http://www.lerup.com/printfile/ can apparently use Ghostscript to print to other sorts of printers. I have not tried that, as my Xerox is a true postscript printer - not one of the cheaper ones which emulates postscript.
If anyone is aware of a better source of design data for Horns, I too would be interested, although Paul is held in
very high reguard by the amateur radio community, so anything he writes can be trusted, unlike a lot of the junk written by radio hams - especially on antennas. Paul knows his stuff!
Dave, G8WRB.