Adaptive Notch Filter Based on Electrically Variable Components for EMC

The use of a notch filter has significant advantages in cases where EMI is expected at a certain frequency and EMC has to be achieved. Notch filters provide high attenuation for a narrow specific frequency band, so they are very application-specific. In the case where the emission behavior changes over time, the notch filter’s effectiveness may be reduced. The ability of the filter to adjust itself to changing operating conditions will, therefore, significantly increase its efficiency. Such an adaptive notch filter can be part of a complex system that operates under a principle similar to cognitive radio. This study presents the electrically variable capacitor and inductors that can be used for such a filter. The proposed elements are examined within the assembled notch filter prototype via conducted insertion loss measurements for standard load/source impedance.