A step-recovery ("snap") diode works on the principle of stored charge in
the diode. During the forward biased half of the AC waveform, the diode is
a very low impedance and it stores excess charge; during the reverse biased
half of the waveform, the diode remains a low impedance until the stored
charge is depleted, at which time the diode "snaps" into high impedance.
This snap acts much like a spark-gap transmitter, in that a tremendous
number of higher order harmonics are generated. In general (and there are
ways to enhance this), the power available from any harmonic is around 1/n *
Pin, where n is the order of the harmonic and Pin is the RF power input to
the diode.

Biasing the diode simply varies the point on the reverse cycle of the AC
waveform where the diode snaps. For maximum power, you try to get the diode
to snap at the peak of the waveform. However, by varying the diode bias,
you can get it to snap before or after the peak of the waveform. Generally
you can get it to snap plus or minus about 30 degrees about the peak before
the snap action degrades.

60 degrees of phase shift is nothing to talk about unless you are working
with the 10th harmonic, which means a phase shift of 600 degrees. Now
you've got something to work with.

Jim