Compact and high-performance low-temperature co-fired ceramic balun filter using the hybrid resonator and symmetric four-port network

A very compact low-temperature co-fired ceramic (LTCC) balun filter is designed based on the simple method proposed in this study. The balun filter consists of four compact LTCC hybrid resonators. Owing to the compact LTCC hybrid resonator, the balun filter with centre frequency at 2.2 GHz exhibits a compact size of 1.22 0.76 0.758 mm. In addition, the balun filter has demonstrated good amplitude and phase imbalances of less than 0.4 dB and 3.2 in the passband, respectively. A wide stopband suppression higher than 20 dB from 3 to 8 GHz is also obtained. Both simulation and measurement results are given in the study.