LTCC Bandpass Filter With Wide Stopband Based on Electric and Magnetic Coupling Cancellation

This paper presents a new method of using electric and magnetic coupling cancellation to extend the stopband of bandpass filters (BPFs). The mechanism is theoretically analyzed based on the lumped-element equivalent circuit. Due to the cancellation of electric and magnetic coupling between two resonators, three transmission zeros (TZs) can be generated and controlled by manipulating the coupling strength. Using the proposed method together with source-load coupling, a low temperature cofire ceramic (LTCC) BPF is designed with four TZs at the passband edges and within the stopband, resulting in high skirt selectivity and harmonic suppression. Due to the LTCC multilayer structure, the filter size is 0.054 λ_g*0.045λ_g*0.013λ_g, or 2.48 mm ×2.02 mm ×0.6 mm. The theoretical, simulated and measured results of the LTCC BPF are presented to validate the proposed design.