Synthesizing a Multiband LTCC Bandpass Filter With Specified Transmission- and Reflection-Zero Frequencies

This paper presents a vertically expandable low-temperature cofired ceramic (LTCC) bandpass filter (BPF) structure to increase the number of operating bands of the BPF without changing the area of the footprint. To design efficiently the proposed LTCC BPFs with highly configurable passbands and stopbands, a new method of synthesizing multiband BPF prototypes with specified transmission- and reflection-zero frequencies is developed. A dual-band BPF and a triple-band BPF were designed and implemented in LTCC. Both BPFs have the same area of 1.25×2.0 mm2. Comparisons of the S-parameters among the synthesized prototypes, postlayout simulations and measurements exhibit a strong correlation.