Small size 2.4 GHz ISM-band LTCC filters with transmission zeros

In this paper the theory of bandpass filters based on parallel resonators coupled by means of admittance inverters and further enhanced with cascade triplets (CT) is applied to the design of small size filters in LTCC technology. The parasitic coupling between stripline resonators is analyzed in detail and used to introduce transmission zeros in the filter response. Two realizations for the 2.4 GHz ISM-band are presented. Thanks to the introduction of transmission zeros, the filters show good attenuation at the GSM, PCS and WCDMA bands, which enables their use in ISM transceivers integrated in cellular phones.