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568z o 2005 15th In. Crimean Conference 'Microwave & Telecomrnunication Technology"(CnMiCo'2005).12-16 September, Sevastopol, Crimea, Ukraine568 ,?c 2005: CriMiCo'2005 Organizing Committee; Weber Co. IEEE Catalog Number: 05EX10)89

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(21 Hartmann C. S. A fast accurate method for calculating theSAW and bulk wave radiation admittance of a SAW trans-ducer- Proc. IEEE Ultrason. Symp., 1988, p.39-46.

[3] Wright P. V. A new generalized modeling of SAW transduc-ers and gratings - Proc. 43r Annual Symp. Freq. Control,1989, p.596-605.

[4] CUHU4biHa T. B., WepMaeuHa E 10. SAW-filters usingacoustic guides - Proc. Intern. Symp. ISEFPMA-94, Russia,Moscow, 1994, p.PO3-28.

[5] CuHuIwIHa T. B., Opnoe M. M. VOccnegoBaHMe BnNJqHI45 3neK-TpOAHOR CTpyKTypbt Ha napameTpbi aKyCT4ecKoA BoJnHbl BCUnbHbIX nbeo3oneKTprpax -V3BecTmq BY30B. Cepms MaTe-PmanblI 3neKTPOHHOA TeXHlKf, NQ1, MocKBa, 2004, c.67-69.

THE SECOND ORDER EFFECTSIN LOW-LOSS SAW FILTERS

Sinitsyna T. V., Praporchtshikov V. V., Shermaguina E. U.((BUTIS-M>), Ltd.

Moscow- 121357, RussiaPh.: (095) 411-96-08, e-mail: Butis.M@ru.net

Abstract - Presented in this paper are the results of re-search of the second order effects in low-loss SAW filters ap-plied in the input channel of communications systems.

1. IntroductionNowadays low-loss filters on surface acoustic waves (SAW)

are widely used in cellular phones, systems of cable and chan-nel (ethereal) television, radiolocation, executing the function ofsignal frequency selection. The small insertion attenuation (lessthan 6 dB) in such filters is provided by special design, whichcombines inter-digital transducers (IDT), reflectors, couplers [1].In spite of design variety, wide frequency band (20 MHz ... 2GHz) and wide passband (0,04%... 14 %), methodologicalapproach to the analysis of their characteristics is identical. P-scattering matrix is used for calculation of each frequency-selective unit, being a part of the design [2,3]. In this work thesecondary effects, which influent on the basic performances ofSAW filters and ways of their compensation are considered.

11. Main PartUsually at calculation of low-loss SAW filters characteristics

the second order effects influential directly in a level of an inser-tion attenuation in a filter passband are taken into account: non-zero resistance in the transducer electrodes and wave propaga-tion loss. Our researches have shown that at implementation ofSAW filters with non-optimum for the given design by combina-tion of parameters (for example, the ratio of a center filter fre-quency, the bandwidth and form-factor of characteristics) hap-pens essential distortions of their performance. So for low fre-quency (20 ... 50 MHz) SAW-filters with maximum bandwidthbased on the application of a reversible coupler, distortion ofthe characteristic takes place in high frequency rejection bandbound to excitation of a spurious volumetric mode. The similareffect takes place in designs based on a U-shaped coupler.Minimization of this effect is carried out by the corrugation of theplate backside. In order to design high frequency (above 500MHz), narrow-band (about 1 %) SAW-filters based on of longi-tudinal - coupling resonators, IDT with large number of elec-trodes are used. In this case the matching with 50-Om channelis provided using the smail transducer aperture. The researcheshave shown that at the IDT apertures less than 10 wavelengthsshould be considered in wave-guide distributional pattern [4].Presented in Fig.1 are the experimental filter responses of 35TV-channel obtained with (continuous line) and without (dottedline) acoustic waveguide conditions considered. The analysis ofexperimental data has revealed two secondary effects, whichare not taken into account by the developers of SAW - devicesbut much influential on the characteristics shape. It is a disper-sion of a wave velocity from frequency and dispersion of a cou-pling coefficient from the film width [5]. The first effect deter-mines a position of the first nulls and side lobes of a filter re-sponse and specially has an effect at extreme broad passband.The second effect is swept up using large film widths and de-termines the response shape in the filter passband.

111. ConclusionThe main principles of the low-loss SAW-filter calculations

are considered. The analysis of secondary effects and thecompensation methods are described.

2005 15th Int. Crimean Conference "Microwave & Telecommunication Technology" (CriMiCo'2005). 12-16 September, Sevastopol, Crimea, Ukraine© 2005: CriMiCo'2005 Organizing Committee; Weber Co. IEEE Catalog Number: 05EX1089 569