Hans Nusbaum, DJ1UGA, has published in  a simple noise source for VHF &
up. But he used a manhattan style PCB. This didn't work above 1GHz. I used
a commerical 50 Ohm striplineboard.
The unit covers the frequency range up to 3.6GHz within +-1db, the ENR is about 32dB.
 HF-Messungen für den Funkamateur, VTH-Verlag, Germany