Wideband improvement of capacitively coupled filters

This paper describes an open-end coupled structure that yields a wide capacitance range enabling the design and realization of bandpass filters having a relatively wide passband. The proposed structure enables coupling strength to be flexibly controlled within a relatively large range through an adjustment of the stub length. The added advantage is that this is realized on a single metallization layer. Conventionally end-coupled configurations are precluded from wide passband applications as tight coupling between adjacent resonators is needed. The measured performance of the bandpass filter implemented using the proposed technique yields a filter with a relatively wide passband, low passband insertion-loss ¿ 2 dB, return-loss > 10 dB, steep skirts and high out-of-band rejection.