Looking for some waveguide expertise here

[wkb]

Picked this up at a local ham fest.  Not being a microwave nut by any stretch of imagination I wonder what this stuff does? OK, horn antennes but
there is more to it.  Maybe something with polarisation ?? No clue..

Hope the images are enough clue to the initiated...

[wkb]

more pics

[kazam]

45 degree polarization
Septum could be cross-polarization suppression. CP polarizer if made of metal but doesn't look like it.
Dielectric around edges I'm not sure but could be far-field sidelobe suppression. Or cross-pol. Or both!
Radome is most likely just for protection or to keep pressurized air inside. This prevents dust from entering the waveguide.
Looks like radar stuff for X-band. 10GHz.

[radar_macgyver]

That's a double ridge waveguide. The ridge increases the bandwidth that the waveguide can transmit without multiple modes (ie, without dispersion). Same goes with the ridges inside the horn flare - these extend the bandwidth of the horn. They work just like a Vivaldi antenna. You don't often see double ridge waveguide in radar, so this could be X-band satcom equipment, or EW or radar warning receiver antennas. Very cool find!

Edit: septum polarizers are not normally flared, they usually have a 'stair-step' appearance. They're used to create circular polarization. You'll often find them inside satellite TV LNBs.

[cj]

Looks like the parts you have are from this type of feedhorn.

CJ

[wkb]

The Heelweg picture shows a very similar but a lot bigger horn.

Wilko