The module upconverts input RF 0-3GHz to 4GHz (using 4-7GHz LO), then amplifies and filters the IF and finally downconverts the 4GHz to 228MHz (using 3.772GHz LO).
It's not a really good design (high losses, poor spurs rejection) but it seems to work.
Design description, design files, simulations, measurements results in the attached file.
Files
SIGN_CONV_rev2_design_pack.zip
design and description of rev2 of the frequency converter
I've uploaded documentation of revision 2 of the module. There are many improvements: 1st mixer was redesigned (now slotline balun is used), also amplifier was improved (it should have better wideband matching) and filters were improved (input filter is now elliptic filter, IF bandpass filter is mostly the same but low pass filter was optimized).
More details in the design description (file SIGN_CONV_rev2_design_pack.zip).