LTCC Wideband Bandpass Filters With High Performance Using Coupled Lines With Open/Shorted Stubs

Two compact low-temperature co-fired ceramic (LTCC) wideband bandpass filters using coupled lines with open/shorted stubs are proposed in this paper. Two conventional coupled lines with open/shorted stubs are used to increase the passband order for the wideband filters. Two independent transmission zeros realized by the open/shorted coupled lines are used to further improve the passband selectivity and harmonic suppression. Due to the 3-D LTCC circuit, the coupled lines and stubs can be located at different layers to overcome the large circuit size. Two fifth-order wideband LTCC bandpass filters centered at 3.1 GHz with multiple transmission zeros are designed and fabricated for verification. The theoretical and measured results are in good agreement and show good in-band performances.