Classical and tuneable band-pass filters using MMIC negative resistance circuits for losses compensation and size reduction

New band-pass filter design techniques are presented using classical passive interdigitated filters. An MMIC active component circuit assists all the filter designs. The MMIC component performs a negative resistance with an associated imaginary part. By using this component, the negative resistance leads to compensation for the losses of the passive filter while the imaginary part leads to reduction of the length of the resonator. Two filters, implemented in microstrip and coplanar technologies, have been designed and tested to demonstrate our approach. In the last step, we have developed a frequency tuneable band-pass filter.