802.11b Horn Antenna Designer

Frequency

WaveGuide

Twice h is the wavelength of the cutoff frequency, it should be greater then the signal wavelength. If you are not using some Tetra Brik or piece of hardware at your disposal, you should use standard waveguide size (as WR340 3.4"x1.7"). The rod of length Lambda/4 is placed at Lg/4 of the bottom of the guide. Lg is the wavelength of the signal in the guide (1/sqrt(1/Lo^2-1/Lc^2) with Lo, the wavelength in open space and Lc, the cutoff wavelength (2*h)). The guide is Lg/2 long.

h m (big side of the wave guide)
e m (small side of the wave guide)

Box

Let's suppose you put your horn inside a box. The open side is H*E and the depth of the box is P. The horn shouldn't be too open so that the wave in the axis is not too far away when it reaches the end of a side. (uh?) As far as the mechanic design is concerned you can place the feed inside the box (it is more robust, but the horn is shorter, hence more open) or outside (it is more fragile).

H m (big side of the box)
E m (small side of the box)
P m (depth of the box)
Check this if the waveguide is inside the box

Results

Check if your horn is not too open. I don't know when it become unacceptable (lambda/8 is recommended, but I don't know what to measure; I took the hypotenuse of P-H/2 versus P). Aristide Clairembart (obviously a pseudo ;-) wrote me that I had to compare the distance along the axis and the distance along an edge (SQRT(H*H/4+E*E/4+P*P)). However, it doesn't seem to matter much as we used a very open horn with success on a 16 km link (LittleBigHorn at LouvainWaterloo)

Sides dimensions : two of each.

Cutting two sides at once in a sheet.