| Γ Γ | 2 = | Z N − − Z 1 Z N + Z 1 | 2 | Γ Γ | 2 = | R N + j X N − − ( R 1 + j X 1 ) R N + j X N + R 1 + j X 1 | 2 R N is the negative resistance of the diode − r. Assuming the filter is matched to the diode so X 1 = − − X N then the gain is G P = | Γ Γ | 2 = ( r + R 1 ) 2 + 4 X N 2 ( r − − R 1 ) 2 The VCNR reflection amplifier above is stable for R 1 < r . while a CCNR amplifier is stable for R 1 > r . It can be seen that the reflection amplifier can have unlimited gain, approaching infinity as R 1 approaches the point of oscillation at r . This is a characteristic of all NR amplifiers, contrasting with the behavior of two-port amplifiers, which generally have limited gain but are often unconditionally stable. In practice the gain is limited by the backward "leakage" coupling between circulator ports.