The purpose of this letter is to investigate the stability conditions of the active two port networks having some restrictions on load and source terminations, and then they have been obtained. Next, these results and the previous stability coditions are investigated, and then the new combined stability condition are proposed.

The purpose of this letter is to investigate the stability of the active two port networks having some restrictions on load and source terminations, and the stability conditions having two inequalities have been obtained. As the terminations making the active two port networks stable can be obtained from these inequalities, these stability conditions are very useful for designing high frequency amplifiers, especially, tuned amplifiers.