A Miniaturized Bandpass Filter with Wideband and High Stopband Rejection Using LTCC Technology

A compact low-temperature co-fire ceramic (LTCC) bandpass filter based on quarter-wavelength steppedimpedance resonators (SIRs) and lowpass loading cells with improved wideband and high stopband rejection level is proposed and demonstrated in this work. In the implementation, two low impedance SIRs are placed on different layers, they generate strong capacitive coupling and form a wide passband. Further, the width of the stopband is improved by loading lowpass cells, while two extra poles formed to improve the passband response simultaneously. The final simulation proves the proposed filter has a passband bandwidth of 67.5%, while the circuit size is only 1.68mm×0.8mm×0.48mm, which has clear advantage in bandwidth and size to other similar LTCC based filters.