Just wondering what kind of trouble could lie ahead when combining MMIC power amplifiers with external baluns. A low-loss balun has poor isolation... could this cause an oscillation? would it be a transient thing on startup and then die down or could it oscillate all the time? Does it matter that the amplifiers are already unconditionally stable? Asking for a friend...

If isolation doesn't matter in this case, why does it matter when you combine amplifiers in-phase or in quadrature?

Steve