A miniaturized LTCC bandpass filter with low insertion loss and high image rejection within 6.5 to 7.1GHz frequency range

A low-temperature-cofired ceramic (LTCC) bandpass filter with low insertion loss and high image rejection is presented for super heterodyne microwave receiver within 6.5-7.1 GHz band. By improving the filter cell structure, two transmission zeros can be generated to achieve wide-band image suppression from cascading filter cells. The presented method provides the design flexibility of locating these transmission zeros distributed in the lower and upper stopbands. To reduce insertion loss and size of the filter, a miniaturized LTCC three-stage bandpass filter with two transmission zeros in lower stopband has been implemented for experimental demonstration. The measured insertion loss is less than 1.0 dB at 6.8 GHz, the measured image rejection from 5 to 5.6 GHz is more than 42 dB, the input/output VSWR is less than 1.5. The size of the miniaturized filter is only 2.5 mm × 2 mm × 1.2 mm. The process yield of the LTCC filter is more than 90%.