Nonlinear behaviour of active microwave filters

Active microwave filters are a potential solution to the problem of producing miniature low loss MIMIC filters. By using active negative resistance circuits coupled into low Q resonators it is possible to cancel filter losses and produce filters with apparently infinite Q factor. However, this situation is only true for small signal excitation. At large signal levels, the nonlinear characteristics of active devices produce intermodulation and cross modulation distortion. This paper present results of a characterisation of the nonlinear behaviour of active microwave bandpass and bandstop filters using both computer simulation and experimental measurements