Use of stable tunable active feedback analog filters in frequency synthesis

An apparatus for generating a signal, the apparatus comprising:

• a synthesizer that generates a synthesized signal having a plurality of frequency components comprising a fundamental frequency component and a plurality of spurious frequency components;
• an analog filter connected to process the synthesized signal, the analog filter having a passband that filters the synthesized signal, the analog filter comprising a tunable, active feedback circuit having one or more variable resonators and a variable gain block connected in a signal loop;
• and
• a controller connected to the synthesizer and the analog filter, the controller comprising instructions to:
• tune the analog filter such that the passband of the analog filter overlaps one or more desired frequency components of the plurality of spurious frequency components, the analog filter being capable of generating a relative bandwidth of the passband of about 1% or less.