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Small-Size Low-Loss Bandpass Filters on Substrate-Integrated Waveguide Capacitively Loaded Cavities Embedded in Low Temperature Co-Fired Ceramics

V. Turgaliev, D. Kholodnyak, J. Müller, and M.A. Hein

Journal of Ceramic Science and Technology, Vol. 6, No. 4 (2015), pp. 305-314

DOI: 10.4416/JCST2015-00053

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Abstract

The design of microwave filters for portable electronics is complicated by conflicting requirements that must be met simultaneously such as high selectivity, low insertion loss and compact size. Substrate-integrated waveguide (SIW) technology allows the design of low-profile high-Q resonators and low-loss filters based on this. However, SIW filters are not well suited for telecommunication applications because of their remarkably large size in plane. The size of a SIW cavity can be dramatically reduced with the use of capacitive loading. Capacitively loaded cavities (CLCs) operating in the TM110 mode are shown to be as small as 1/8 of the guided wavelength and even smaller, i.e. comparable in size with lumped-element resonators. Although the unloaded Q-factor decreases proportionally to cavity size, miniaturized CLCs can exhibit a much higher Q-factor than that of lumped-element resonators. This paves the way for designing small-size and low-loss filters for wireless communications and different applications. Miniaturized capacitively loaded SIW cavities are favorably implemented by means of low-temperature co-fired ceramics (LTCC) technology. The goal of the paper is to demonstrate the manifold possibilities and flexibility offered by LTCC technology for the design of advanced microwave filters on CLCs. Different design and manufacturing aspects are considered. Various design examples of high-performance LTCC resonators and filters for single- and dual-band wireless applications are presented. The designed resonators and filters were manufactured using the commercial DuPont Green Tape 951 LTCC system. The LTCC filters on miniaturized CLCs are shown to be advantageous with regard to small size, low loss, and absence of spurious response over a wide frequency range.

Keywords

Substrate-integrated waveguide (SIW), low temperature co-fired ceramics (LTCC), capacitively loaded cavities, dual-mode resonators, bandpass filters.

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