Does anyone know how to design Horn Antenna operating A 100Mhz?

You should be able to scale up the dimensions of a UHF horn. One with any appreciable gain at 100MHz would be very large though!
I'm mentally scaling up horns I use at 10.5GHz and thinking >10m^2 aperture size.

Brian.

First thing that came to mind: https://imgur.com/a/baZDw

Me, the first thing that came to my mind was:

https://en.wikipedia.org/wiki/Holmde...ew_Jersey.jpeg

WHY do you want a waveguide horn?
Something like a helical coil antenna will be much smaller (due to the slow wave structure) and have high gain too.

I have a 2 GHz horn, and it is impressively large. Not sure just how large a 100 MHz one would be, but it would be ginormous.

I wonder how big and how efficient a 100 MHz dielectric filled horn would be? Maybe a horn filled with water? That should be about 9.3 times smaller than an air filled horn...you might end up with one only the size of a small desk

Hi biff44, do you know a reference I can use for the computation of the dimensions of horn antenna?

1 second google research: http://hornantennacalculator.blogspo...alculator.html

Hmmm,

What kind of horn, how much gain, any pattern requirements? Provide more information and you may get more useful responses. In general, as was pointed out above, a horn at 100 MHz is likely going to be physically large and may not even be practical.

Regards