Category Archives: 3cm

10 GHz Dielectric lens Feedhorn

I’m working on a simple, waterproof, reproducible design for a 10 GHz dish feed for folks who are taking part in the group buy project to build F6BVA 10 GHz to UHF transverters. This uses a probe launch into a round waveguide machined from solid aluminium. The lens is made from Rexolite 1422, which is a free-machining cross-linked polystyrene with well-defined relative permittivity and a loss tangent of about 0.0004. This one is designed for a rather flat offset dish I have with equivalent f/d about 0.75, but I will be doing some for more common offset dishes

Finished 10 GHz feedhorn with Radiall SMA connector

The body is turned and bored from a bit of aluminium round bar

The flat area is too large on this one, I’ll make it narrower on subsequent versions so I don’t have to shorten those M2.5 screws

WR90 to SMA transition

I needed a couple of transitions, so decided to try to make a very simple narrowband design, optimised for 10368 MHz with low loss and a good match over a few hundred MHz. I ran up a design with rounded corners to the cavity to make it simple to machine using an 8 mm slot drill. I chose aluminium for the body as it performs well, although without anodising, it is going to need protection from the elements. I used some good quality Radiall SMA four-hole flange-mount sockets.

Although this looks a simple part, the instructions I make for myself show the level of detail.

I’ll publish the measured performance soon. So far, I can get around -23dB across ±100MHz. Once optimised, I will have some of these for sale to bona-fide experimenters. Email neil@g4dbn.uk for details

One of the completed horns ready for testing
CAD model in Fusion360
Modelled through loss and return loss from OpenEMS