I've bought a few 50MHz-6GHz directional coupler(SEDC-10-63+), each for 75$. Here is a picture of this expensive coupler!

Unfortunately one of these couplers was not working from the beginning so I decided to put the cover up and get a glimpse of inside. The problem is I cannot understand what is this big black component(Probably a ferrite) do And how it contribute to the coupling or directivity

##Coupler Inside

I also wondering if the cover do anything more than simple a cover. The top cover feels like a plastic but sounds like a ceramic object.

##Cover

Thanks