Compact Multi-Layered Wideband Bandpass Filter with Multiple Transmission Zeros

A miniaturized multi-layered wideband bandpass filter (BPF) based on the low-temperature-cofired ceramic (LTCC) technology is proposed in this paper. The proposed filter consists of a T-shaped short stub and a pair parallel transmission lines. Owing to the multi-path effect, multiple transmission zeros can be realized near the passband for enhanced selectivity. A wide-band filter from 3.59 GHz to 8.21 GHz is designed, fabricated and measured. The measured results show that the center frequency is 6 GHz with a fractional bandwidth (FBW) of 74.8%. Three transmission zeros were introduced near the passband, located at 2.1 GHz with 36.25 dB rejection, 9.25 GHz with 27.02 dB rejection, 10.56 GHz with 28.58 dB rejection.