Dear Forum
For a reference frequency multiplier from 5 GHz to 10 GHz, I planned on using the HMC561 first. After measuring the phase noise before and after the doubler, I noticed a very pronounced increase in phase noise between 200 kHz and 20 MHz due to the device. So after a quick search in your frequency multiplier database, I came up with the HMC369, whose limited frequency range and easier use is more suitable for our purpose. But, unfortunately, the same phase noise pronunciation is observable with this device, which leads me to the question: Am I doing something wrong or is this to be expected from these devices (despite the datasheet information)?
Both frequency doublers were evaluated using their respective evaluation board and the feeding 5 GHz is absolutely OK. The input amplitudes have been checked multiple times, as was the gate voltage and sequencing in case of the HMC561.
In the attached picture, the light blue curve is the input signal phase noise (@5 GHz), the green curve is the HMC561 output phase noise, purple is the HMC369 phase noise and the red curve is the output phase noise of our Anapico APSIN20G signal generator at 10 GHz (just for comparison!). Encircled is the problematic phase noise region which in an ideal world should follow the light blue curve with an offset of +6 dBs.
Any suggestions?
Thanks in advance and best regards,
Fabian
