Low-insertion-loss high-frequency surface acoustic wave filter

Abstract

The invention discloses a high-frequency low-insertion-loss surface acoustic wave filter, belongs to the technical field of surface acoustic wave filters, and comprises a structural design of the filter and an optimization method for reducing in-band fluctuation, reducing insertion loss and improving out-of-band rejection performance. According to the structural design of the filter, four parallel resonators P1-P4 with the same structural parameters and four series resonators S1-S4 with different structural parameters form a 'T + pi'-shaped structure so as to improve out-of-band rejection and optimize a rectangular coefficient. The optimization method for improving the performance comprises the steps that each resonator unit uses a thick metal film interdigitated electrode structure to suppress the wave velocity of love waves and improve the strength of Rayleigh waves; the duty ratio of all the series resonators is improved, and the reflecting grating period is shortened to reduce transverse mode interference; and the positions of transverse mode frequency points of the resonators are changed by adjusting the interdigital logarithm of the series resonators, so that when different resonators are cascaded, loss introduced by a transverse mode is superposed in a staggered manner, and in-band fluctuation and insertion loss are reduced while out-of-band rejection is improved.

Description

technical field [0001] The invention belongs to the technical field of surface acoustic wave filters, and in particular relates to the design of high-frequency low-insertion-loss filters above GHz. Background technique [0002] At present, the surface acoustic wave (SAW) filter is more and more widely used in line with the development of mobile communication technology due to its small size, high frequency and low insertion loss. Usually, piezoelectric materials with high sound velocity and high electromechanical coupling coefficient are used to increase the center frequency of the filter, reduce insertion loss, or use a diamond-containing multilayer film structure, the purpose of which is also to increase the wave velocity of the surface acoustic wave. However, the manufacturing process of the multilayer film structure is relatively complicated, and the high electromechanical coupling coefficient often enhances the intensity of the required surface acoustic wave mode, and t...

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Problems solved by technology

However, the fabrication process of the multilayer film structure is relatively complicated, and the high electromechanical coupling coefficient often enhances the intensity of the required surface acoustic wave mode, and the intensity of other miscellaneous mode modes will also be enhanced, which will undoubtedly increase the insertion loss of the device.

[0003] Compared with the longitudinal coupling structure (LCRF), the SAW filter of the ladder structure (Ladder) has more flexible bandwidth design, and has lower insertion loss than the dual in-line structure (IIDT), and can improve the bandwidth by adjusting the cascade. External suppression, but the cascading of the same resonator will make the stray mode intensity in the passband superimposed and the squareness is large

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