A miniaturization method of parallel coupled-line filters using lumped capacitors and grounding

This paper proposes a new miniaturization method of the parallel coupled-line filter by using lumped capacitors and grounding. The proposed method can dramatically reduce the size of the resonators in the parallel coupled line filter. In addition to the size reduction, an excellent suppression of spurious harmonic responses, which are inherent in this type of filter, is achieved with improved skirt characteristics. To show the validity of the proposed method a filter, which has a center frequency of 900 MHz and an FBW of 10%, is scaled down to half its original dimension. The measured result shows a high level of agreement with the theory.