Compact balanced combline bandpass filters with two independently controllable transmission zeros in LTCC technology

In this paper, the design of compact balanced combline bandpass filter in LTCC is presented. The mix coupling effect is utilized to create two transmission zeros that can be located independently in either the upper or lower stopband. Also, the effect of non-adjacent line coupling is minimized in an efficient way. The proposed filter is implemented using LTCC to achieve very compact circuit size, in which the combline line lengths are as small as λ/15. Specifically, two 3rd-order balanced combline bandpass filters with two transmission zeros on the same side or on the opposite side of the passband are implemented in LTCC with chip size of 2012. Good balance performance, low loss, good selectivity, and compact size are achieved.