To help those who are building for 24GHz I'll put up some information on building WG filters. To start here is a photo of some of my collections. These are primarily commercial filters which are typically on 22-23.6GHz. The large one at the back is actually a 4 section cavity filter. The long one in the middle is a 5 section 'post' filter. Single section ones like this are easy to make and great for cleaning up the LO signal. If you are using a high IF then a couple of sections will normally be good enough for the signal.
The second is a montage of my favourite, easy to build, filter with 3 sections. This is simpler to build than the 3 section iris type filter but with slightly lesser performance. 24048 is about -16dB. 23760 is -30dB. So, this filter is better for a 432 or 1296MHz IF.
The original is, I think, due to DB6NT (UHF Unterlage Teil IV).
Construction information here but one thing to note is that
the copper plates are a tight fit in the guide and,
though it doesn't look it from the photos, there is no solder
in the guide. I used SMD solder cream to make the joints.
All you need is a hacksaw with a new blade and some 1mm copper plate, a piece of WG20(WR42) about 50mm inches long, some small (1.6/2mm) brass or copper screws and the tap to match (model shop) and a couple of flanges. The four plates are 7mm apart, the middle two project 8.3mm into the guide, the outer two 6.5mm. On the center line of the broad face of the guide you need three screws between the four plates and two spaced 4.5mm from each of the two outer/end plates. Dimensions are important so use a magnifier (you can get 35mm film/slide viewers with a built in scale) to get these right. Make the ends square and then cut the slots from the narrow face carefully until just before the marked length and then use a scalpel/knife to go the last fraction of a mm.
Make the holes for the screws and tap. Care! Copper guide is soft so it is easy to ruin the thread. Clean the whole assembly and the brass plates. Mount the first lock nuts on with steel screws, the dirtier the better, insert the plates into the guide - if you got this right then you'll need to use force to push them in - and put on the flanges. Using the some solder paste (SMD) make up all the joints - flanges, nuts and plates. Put the whole assembly on a hotplate until the joints are good and cool/clean up. Change the screws for brass or copper (better) or silver plated (better still) and add the second lock nuts. If required, finish the flange/guides using a flat plate and fine emery paper.
Tuning it up is the hardest part if you don't already have a known good source on 24192. The best way is to get someone else to do it!! Then once you have one good filter you can align your own later using a signal source and your own receiver. On mine the screws are all about 1.5mm into the cavity.