Shielded attenuator box
well i would use grounded coplanar waveguide instead of microstrip...it has inherently less leakage problems.
The manufacturer offers a microstrip drawing only. Even so the pcb thickness must be 0.254mm. It's not my knowledge to make a calculation for CPW.
Now I think attenuators over 6GHZ are very expensive because they are CPW.
You don't say how you want these attenuators, but from what you say it looks like you are trying to make cheap set of 'lab' type attenautors for use in testing. If this is the case then you would be much better off getting a coxial attenautor something like the BW series. They might seem expensive, but when you add in the cost of boards for the surface mount components, and the cost of connectors that will work well at 10GHz the cost will not be that much different and you will not have as good an attenautor. The attenuation change over frequency may not look that much different between the two, but the VSWR of the connectorised attenuator is verymuch better, partiicularly at 10GHz, right where you want ot use it, and by the time you have it on a board with connectors it won't get any better.
If you do need a PCB mounted attenuator, the board layout given by Minicricuits is already coplanar waveguide, so no need to change that. If you keep the box small you should not need to use any absorber material.
The shielding can be as simple as some copper foil wrapped around the whole assembly, take care not to short out the components.
I really want to make a set for my lab. It seems like I do not really find the BW series at a good price in Europe. How about jyebao.tw. I found on ebay in UK a shop ( rfshopuk) from which I could take a set (3,6,10,20 db) up to 10GHZ. The problem is that I need exactly between 10 and 10.5Ghz.