Comb Filter Saw-Resonator Traveling Wave

Abstract

Owing to the use of surface acoustic waves, the frequency range of this type of filter is expanded to the high frequency range and can reach several gigahertz. To implement filters on surface waves, piezoelectrics like a quartz plate are used. However, quartz is rarely used for the manufacture of broadband filters. Barium titanate or lithium niobate is commonly used.The difference in the operation of SAW filters from quartz or piezoceramic filters is that not a volumetric oscillation of the piezoelectric is used, but a wave propagating over the surface. In order to prevent body waves that could distort the frequency response, special constructive measures are taken. Most of the advantages of SAW devices are directly related to their physical structure: low weight and dimensions; linear (or defined by requirements) phase; shape factor approaching unity (very high squareness); exceptional out of-band suppression; temperature stability. Since the center frequency and the shape of the frequency response are determined by the topology, they do not require complex settings in the equipment and cannot be upset during operation. Manufacturing technology compatible with semiconductor manufacturing allows them to be produced in large volumes with high reproducibility. Filtering devices on distributed components are considered. Since narrow band filters are constructed on surface - acoustic waves, there are difficulties in providing the vertex of the amplitude - frequency characteristic uniformity. When designing and creating new high frequency electronics components, there is a need to reduce filter losses and harmonization. Offered the design and mathematical model of a comb filter based on a ring resonator of surface - acoustic waves and two waveguides on surface - acoustic waves, which are connected to a ring resonator at opposite points taking into account integral losses. This model helps to consider and calculate the propagation of waves inside the annular resonator in the light of losses. A topological scheme is described, which is described by the distribution of the energy of the signal and the coefficients of division. The division coefficients are represented as mathematical relations. The solutions of the amplitude and phase expressions by the method of successive approximations are presented. Reducing the loss in the filter and reducing the effect of  the partition coefficient lead to an increase in the figure of merit of the ring resonator, which allows to take this into account when designing, since the characteristic moves to the range of higher damping values. We get a result that significantly reduces the bandwidth attenuation of the filter due to the loss reduction. The result obtained is described in the form of   a linear circuit with feedback. The obtained characteristics are inherent in the comb filters, and the result is explained by the fact that the investigated structure is presented in the form of a linear circuit with delay and feedback. Also, it can be  concluded that the advantages of the SAW are light weight and dimensions, temperature stability and relative ease of design and manufacture. 

Keywords

References

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Copyright (c) 2020 Олександр О. Ігнатенко, Юрій А. Грамарчук, Леонід Дмитрович Писаренко (Автор)