This is a bit OT but relevant to the RF & instrument calibration community.
I have developed and I have a few parts sets left for an improved Tektronix SG-504 leveling head unit.
That sig. gen has a relatively pure sine wave (cavity oscillator) and goes to about 1 Ghz, the head (fed by the sig. gen) connects directly to the device under test (eg. the SA) and delivers a fairly pure phase and flat amplitude from 0.5Vpp up to 5Vpp into a 50 ohm load.
My improved remote head unit now gives +/- 0.05dB typical flatness across the Ghz range for calibration of 'scopes, SA's, VNAs or power meters . For special requirements I can get that down to +/- 0.025dB flatness, but it takes care/time as stub & resonance tuning is required to compensate for each BNC connector' s tolerances. SMA connectors are optional but performance differences to tuned BNC are minimal at the Ghz range.
A cal cert. graphing the head flatness across the Ghz range for variations of 0.03dB or more is included so the user can have good certainty over any particular CW frequency's absolute amplitude. The graph functions like a correction factor as found on noise figure generators or RF power detectors for precise work.
I have parts for a few left, contact me if you're interested.