Synthesis and Design of LTCC Filtering Balun With Wide Stopband

This brief presents a synthesis method to design compact low temperature co-fired ceramic (LTCC) filtering balun with harmonic suppression. To achieve wide upper stopband, the design equations are driven based on the schematic. Benefiting from the three-port synthesis method and the flexible 3-D layout on LTCC technology, the coupling matrices at the second and third harmonics are manipulated to achieve the harmonics suppression without extra circuits. Meanwhile, the coupling elements of the passband can keep their desired values. A LTCC filtering balun is designed and implemented for demonstration. A 20 dB stopband rejection from 1.2f(0) to 4.1f(0) is observed. Good agreement between simulated and measured results verifies that the proposed method is suitable and the LTCC technology is reliable for wide stopband filtering balun designs.