Methods for biasing diodes in a microstrip environment

Make an RF low-impedant point using an RF stub. This is a cold point that can be fed with non-RF signals like DC. By transforming this with a quarter wavelength microstrip line to a high-impedant point that doesn't influence the operation of the amplifier or mixer. Or you could use it for matching purposes.

I just realized you can even make it better by making it a third order section: use two radial stubs and separate them with another lambda/4 wavelength transmission line. This would have even bigger bandwidth.