360mV pk-pk corresponds to -4dBm, after a 21dB amplifier, it becomes 17dBm (50mW). According to the specification of frequency mixer (ZX05-1L-S+), it may have permanent damage if the RF power is more than 50mW. Therefore, we have been already reaching this threshold due to this 160~180MHz oscillation. This seems to be the reason of demodulation problem when (R1=11Ohm, R2=130 Ohm) are used. A filter to remove this oscillation may help to solve this problem.

We checked again the simulation of this PD up to 200MHz (see attached figure 1). It has voltage noise increase around 120MHz, but this peak is not very sharp. Therefore, we still don't quite understand why we have such large oscillation when (R1=11Ohm, R2=130 Ohm) are used.