Resonant SAW Filter Cavities With Split Gratings for Lower Lobes
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing surface elastic wave filters with resonant cavities suffer from significant secondary lobes in the rejection or transition band, which increase in amplitude as the relative bandwidth is widened.
Innovation Solution
A surface elastic wave filter with resonant cavities is designed using a composite substrate comprising a base substrate and a piezoelectric top layer, featuring internal reflective structures with distinct periods and separation distances, and optionally external mirrors, to reduce the amplitude of lobes in the rejection or transition band.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the relative bandwidth of the filter is widened, then the filter's bandwidth increases, but the amplitude of secondary lobes in the rejection or transition band increases
Solution Approach 1:
The internal reflective grating is divided into multiple reflective networks with different periods arranged in sequence along the wave propagation path. Each reflective network has a specific period (first period, second period, third period, etc.) that creates different resonance conditions, segmenting the overall reflection function into multiple controlled components that collectively suppress lobe amplitudes while maintaining bandwidth
Solution Approach 2:
Different regions of the filter have different reflective network configurations with specific periods and spacing. The first reflective network has a first period, the second has a second period, and so on, creating local variations in reflective properties that collectively manage the frequency response to reduce lobe amplitudes in specific frequency regions while preserving overall bandwidth
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
The filter structure effectively reduces lobe amplitudes by up to 10dB even for high bandwidths, improving the filter's performance and conforming to predetermined templates.
Implementation Method 1
arranged on a piezoelectric substrate, at least two electroacoustic transducers 2a and 2b, respectively input and output
Implementation Method 2
two external reflective gratings 3a, 3b (and preferably only reflective), typically Bragg mirrors
Implementation Method 3
We thus define a plurality of resonant cavities C1, C2 along the wave propagation path, these resonant cavities forming as many poles of filter 1
Data Source
Figure 1~2a
Figure 2b~3b
Figure 3c~3d
AI summary
The invention relates to a surface-acoustic-wave filter (1) employing resonant cavities, comprising a composite substrate (S) formed from a base substrate (S3) and from an upper piezoelectric layer (S1); at least one input electroacoustic transducer (2a) and one output electroacoustic transducer (2b), which are placed on the upper layer; and at least one internal reflective structure, which is placed between the input electroacoustic transducer (2a) and the output electroacoustic transducer (2b). According to the invention, the internal reflective structure comprises a first structure (Pright) comprising at least one reflective grating (RI) having a first period and a second structure (Pleft) comprising at least one reflective grating (R2) having a second period, the first period being greater than the second period.