Novel technique for harmonic suppression in coaxial cavity filters at the excitation port

A technique to improve the spurious performance of coaxial cavity filters is investigated. The technique involves incorporating resonant elements at harmonic frequencies within the coaxial cavity input/output resonators to allow suppression and control of harmonic outputs. From a physical size perspective, these elements are significantly smaller than the resonant elements employed to perform the basic filtering function at the fundamental frequency; thus they impose only minimized degradation to the ohmic losses of the devices and miniscule additional design effort. Obtained results demonstrate significant improvement in the spurious performance, suppressing harmonic outputs; and experimental results verify the concept.