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Multilayer integrated circuits using the low temperature cofired ceramics (LTCC) technology are considered as applied to design of microwave filters and duplexers for wireless applications. Different structures of miniature LTCC filters based on quasi-lumped-element resonators are suggested with a special emphasis to filters with additional transmission zeros. Original design of LTCC duplexer for IMT-2000 handsets is presented. a) ll 23 29 0--~~~~ã ) T CC~~4 ' 4c b)

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Using a combination of right-handed and left-handed transmission lines to design of miniaturized directional couplers (DC) is considered. Design of miniaturized 3-dB and 10-dB quadrature DC and a rat-race hybrid for wireless applications is presented. Design of a dual-band 3-dB DC is reported as well. All the DCs have been designed as fully-integrated multilayer LTCC structures containing no SMD components. I. INTRODUCTIONBackward-wave transmission lines (TLs) are characterized by negative dispersion and considered as 1D metamaterials [1]. They are referred to as the left-handed (LH) TLs whereas conventional TLs with positive dispersion and forward wave propagation are called the right-handed (RH) ones.Using a combination of sections of RH and LH TLs gives an additional degree of freedom that makes it possible to design passive microwave devices with improved performance and some unusual properties. Particularly, it allows i) controlling the spurious response in order to design dual-band devices [1]-[4] or devices, which are free of spurious response within a wide frequency range [5], ii) designing broadband devices [6]-[9], iii) designing miniaturized devices [5], [9].Directional couplers (DCs) find wide applications for various RF and microwave systems. Conventional branch-line DCs based on λ/4 TL sections have large size, especially in low-frequency applications. The size of DCs can be reduced drastically by means of replacing distributed TLs by artificial ones based on lumped-element LC-cells. Employment of artificial RH and LH TLs in a combination seems to be more suitable for practical implementation of DCs and makes possible a more efficient size reduction as compared with using artificial RH TLs only. Moreover, the use of LH TL is indispensable to design of a miniaturized rat-race ring.This paper presents a design of miniaturized DCs for wireless applications. Quasi-lumped-element 3-dB and 10-dB quadrature DCs and a rat-race hybrid based on artificial RH and LH TLs have been implemented on Low-Temperature Co-fired Ceramics (LTCC) boards as fully-integrated multilayer structures without using any surface-mount devices (SMD).Due to periodic resonant properties of λ/4 TL sections, the conventional DCs suffer from spurious responses at the higher

An enhancement technique of quasi-lumped inductance Q-factor is proposed in order to improve loss performance of LTCC filters. Effectiveness of the technique developed is demonstrated by experimental characteristics of a 3-pole bandpass LTCC filter with reduced in-band insertion loss. Figure of merit of a filter is introduced as a universal characteristic that allows comparison of different filters by means of design effectiveness.