Sounds like your transistor was damaged.
If FETs are used outside the specified values they sometimes don't stop working completely. They sometimes just alter their S-parameters.
I would encourage you to change the FET.
The negative voltage lead to a gate current flow what will destroy your GaAs FET immediately. Such FET's are very sensitive to wrong power supply and to electrostatic discharge. So you have to change it...
Sounds like your transistor was damaged.
If FETs are used outside the specified values they sometimes don't stop working completely. They sometimes just alter their S-parameters.
I would encourage you to change the FET.
The negative voltage lead to a gate current flow what will destroy your GaAs FET immediately. Such FET's are very sensitive to wrong power supply and to electrostatic discharge. So you have to change it...
The NE321000 is a junction-FET. This says that there is a PN-junction between the gate and the D/S channel. If you have a negative gate bias, this diode is in reverse direction. So the current is low (below some 10s uA). If you have a positive bias (or in your case a negative channel voltage) the diode is forward biased, what leads to a relatively high gate current. This gate current distroys the gate structure.