Multi-Mode SAW Filter Reflectors for Shear Mode Suppression
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Solution Overview
Problem
Multi-mode surface acoustic wave filters face challenges in suppressing spurious responses due to the shear horizontal mode, which can lead to insertion loss degradation, and existing designs struggle to achieve this without degrading electrical performance.
Innovation Solution
The implementation of multi-mode surface acoustic wave filters with acoustic reflectors having stepped lengths and slanted pitches, which are arranged to suppress spurious responses by varying the reflector finger lengths and pitches, thereby reducing the shear horizontal mode spurious response in the frequency response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If acoustic reflectors with uniform lengths and pitches are used, then the filter structure is simple, but spurious responses due to shear horizontal mode cannot be suppressed
Solution Approach 1:
The acoustic reflectors are divided into multiple sections along the propagation direction, with each section having different finger lengths. This segmentation allows different portions of the reflector to suppress spurious responses at different frequency ranges, effectively reducing the overall spurious response without complicating the manufacturing process
Solution Approach 2:
Different sections of the acoustic reflector are designed with locally optimized finger lengths and pitches tailored to suppress spurious responses in specific frequency bands. This local quality approach ensures that each part of the reflector contributes to suppressing spurious responses at its optimal frequency range
2Object-affected harmful factors
If acoustic reflectors with stepped lengths are used, then spurious responses are suppressed, but the reflector structure becomes more complex
Solution Approach 1:
The reflector is segmented into discrete sections with stepped finger lengths, where each section corresponds to a specific frequency range. This segmentation achieves spurious response suppression while maintaining a relatively simple stepped structure that is easier to manufacture than continuous variable length designs
Solution Approach 2:
The reflector structure incorporates dynamic variation in finger lengths across different sections, allowing the acoustic properties to be tuned for suppressing spurious responses at multiple frequencies. This dynamic design achieves complex functionality through a relatively simple stepped geometric progression
3Object-affected harmful factors
If acoustic reflectors with slanted pitches are used, then spurious responses are suppressed, but manufacturing precision requirements increase
Solution Approach 1:
The reflector pitch is segmented into discrete slanted sections rather than using continuous variation. This segmentation allows for practical manufacturing by defining specific pitch values for each section, reducing the precision requirements compared to continuous slanted pitches while still achieving effective spurious response suppression
Solution Approach 2:
Each section of the reflector has locally optimized slanted pitch values tailored to suppress spurious responses in specific frequency bands. This local quality approach allows manufacturing precision to be focused on achieving the specified pitch values for each section rather than maintaining uniform high precision across the entire reflector
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design effectively suppresses spurious responses due to the shear horizontal mode without significantly degrading electrical performance, as demonstrated by improved transmission characteristics over frequency, maintaining low loss and good out-of-band rejection.
Implementation Method 1
acoustic reflectors having stepped lengths and slanted pitches, which are arranged to suppress spurious responses by varying the reflector finger lengths and pitches
Implementation Method 2
suppress spurious responses due to the shear horizontal mode
Implementation Method 3
A SAW resonator of a SAW filter typically includes an interdigital transductor electrode on a piezoelectric substrate. A SAW resonator is arranged to generate a surface acoustic wave
Data Source
AI summary
Multi-mode surface acoustic wave filters are disclosed. A multi-mode surface acoustic wave filter can include a plurality of interdigital transducer electrodes that are longitudinally coupled to each other and acoustic reflectors on opposing sides of the plurality of interdigital transducer electrodes. The acoustic reflectors include acoustic reflector fingers arranged to suppress a spurious response due to shear horizontal mode of the multi-mode surface acoustic wave filter. For example, the acoustic reflector fingers can include stepped lengths and/or slanted pitches to suppress the spurious response due to shear horizontal mode.