Super Compact Low-Temperature Co-Fired Ceramic Bandpass Filters Using the Hybrid Resonator

A novel low-temperature co-fired ceramic (LTCC) resonator is proposed based on the hybrid resonant circuits. The resonator exhibits a very compact size and is also able to introduce a transmission zero in the filter design. A super compact bandpass filter with high performance was designed at the center frequency of 2.45 GHz and fabricated using the proposed LTCC hybrid resonator. This filter has a very compact size of 0.9 mm 0.688 mm 0.652 mm and exhibits a low insertion loss of less than 1.2 dB in the passband. Moreover, the transmission zero that is located at 4.5 GHz efficiently suppresses the spurious responses. In order to improve the stopband suppression even more, the revised resonator is used for the second filter design. Besides occupying an even smaller volume of 0.76 mm 0.748 mm0.67 mm, the second filter exhibits a wide stopband suppression higher than 35 dB from 3.4 to 8 GHz. In addition to the super compact size and wide stopband suppression, insertion losses of less than 2.5 dB were achieved in the passband. A transmission zero at 5.8 GHz was also achieved.