Dual-band-rejection filter for distortion reduction in RF transmitters

A novel concept of dual-band-rejection filter (DBRF) is proposed with its circuit synthesis procedure and examples of its realization with dielectric resonators and microstrip resonators. A DBRF can make two closely spaced rejection bands and a passband between them, with lower loss than a bandpass filter having the same number of resonators and the same frequency selectivity just around the passband. The DBRF can be synthesized by applying novel frequency-variable transformations to a prototype LPF, and its physical size can be smaller than a simple cascade of two conventional band-rejection filters with different rejection bands. The DBRF can be especially applicable to distortion reduction filter in RF transmitters.