Scaling dimensions of hydrogen horns

[andrew....@googlemail.com]

I notice that the SETI Horn of Plenty is a smaller version of the original Ewen Horn that first detected hydrogen in Milky Way in 1951 – how do horns scale? I’ve tried to look this up on line and can’t get a clear answer – clearly the first part of the antenna near the waveguide is set regarding its measurements – what commercial makers call the coax to waveguide adapter – this has set width and height. However, the horn section that follows until the aperture – can you simply be scaled by any amount from the SETI Horn of Plenty design or does this need to be in exact numbers of hydrogen wavelengths or some other way of scaling the horn?

 

Any help appreciated, as I am (metaphorically as I don’t have hair any more) pulling my “hair” out over this!!

 

Andy

[Dave Typinski]

Why would that part not scale with frequency like any other part of an antenna?
--
Dave


On 1/26/26 03:32, andrew.thornett via Society of Amateur Radio Astronomers wrote:
> ...clearly the

[Adrian]

The scaling of the "flared" section only of the horn scales up or down to the beamwidth of the desired horn as long as the proportions of the original design are kept the same, flare angle etc.. The original Ewen -Purcell  horn had a half power beam width of ~ 10°  for its dimensions of  56 inches (142 cm) across by 43 inches (109 cm) high by a little over 127 inches (323 cm) long for an aperture of a little over 127 in ≈ 323 cm .    see   https://www.astronomynotes.com/telescop/greenbanktour/gbtour17.htm
.  If you wanted to scale it say for a 20° beamwidth  then using a ratio of ~0.5   for the H plane dimension for example the width  would scale then from ~ the 1.4 M Ewen H plane to the smaller O.7 M dimension etc. with the resulting ~20°  beamwidth.