Hello! We use the hmc1197 modulator at a frequency of 460 MHz. At the output of the modulator, the signal constellation twitches, what can this be connected with?
From the shape of EVM constellation, it looks it is from the phase imperfection either on LO phase splitter inside or I/Q paths. In HMC1197 modulator, the 90 degree phase split of the LO is by a polyphase filter. Please check it at different LO frequency since phase quadrature error may vary slightly over frequency. Also check if there is phase error between baseband inputs(ideally 90 deg difference between I and Q) and apply phase adjustment on I/Q path if possible.