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In this paper, we utilize the coupling matrices to design a compact low-temperature cofired ceramic (LTCC) bandpass filter with wide stopband and high selectivity. One coupling matrix at the fundamental frequency is synthesized to obtain required passband responses. The other one at the third harmonic is manipulated to realize wide stopband. Two transmission zeros are appointed at both sides of the passband to enhance the skirt selectivity. They are generated by multiple cross-coupling paths, which are easy to realize in the multilayer LTCC structure. To reduce the circuit size, two coupled quarter-wavelength resonators are folded vertically and horizontally on different layers. An experimental filter is designed for verification. High skirt selectivity and wide stopband are observed in the measurement. Due to the LTCC techniques, the proposed circuit has a compact size of 2~\text mm\times 1.7~\text mm\times 2 mm or 0.042\lambda g\times 0.035\lambda g\times 0.042\lambda g . It is suitable for system-in-package applications. [ABSTRACT FROM PUBLISHER]

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 \(\lambda _{g}* 0.045 \lambda _{g}*0.013\lambda _{g}\) , or \(2.48~{\rm mm}\times 2.02~ {\rm mm}\times 0.6\) mm. The theoretical, simulated and measured results of the LTCC BPF are presented to validate the proposed design. [ABSTRACT FROM AUTHOR]