Surface Elastic Wave Filter Cavities for Secondary Lobe Suppression
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Solution Overview
Problem
Surface elastic wave filters with resonant cavities often exhibit high-amplitude secondary lobes in the rejection or transition band, particularly when attempting to widen the passband, which is undesirable for telecommunications applications.
Innovation Solution
A surface elastic wave filter design featuring a composite substrate with a piezoelectric upper layer and a base substrate, incorporating an internal reflective structure with distinct reflection gratings and separation distances, along with 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 passband width is widened, then the filter can process a broader frequency range, but the amplitude of secondary lobes in the rejection or transition band increases
Solution Approach 1:
The internal reflective structure is segmented into multiple reflection gratings with different periods arranged in sequence along the wave propagation path. Each grating reflects specific frequency components, and their combined effect suppresses secondary lobes while maintaining a wide passband. The segmentation of reflection functions across multiple gratings with varying periods resolves the contradiction between passband width and lobe amplitude.
Solution Approach 2:
Different regions of the filter have different reflective properties through the use of reflection gratings with different periods. The first grating with period P1 targets specific frequency components while the second grating with period P2 targets others, creating localized reflection characteristics that collectively suppress secondary lobes across the transition band while preserving the wide passband.
2Device complexity
If traditional filter structures are used, then the design is simple, but the amplitude of lobes in the rejection or transition band is high
Solution Approach 1:
The reflective structure uses a composite configuration of multiple reflection gratings with different periods rather than a single uniform grating. This composite structure combines the reflective properties of different period gratings to achieve superior lobe suppression performance while maintaining reasonable design complexity through systematic arrangement.
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 proposed filter structure effectively reduces the amplitude of secondary lobes by at least 5 dB, even for high passband widths, improving the filter's performance by minimizing unwanted signal rejection outside the passband.
Implementation Method 1
arranged on a piezoelectric substrate, at least two, respectively input and output, electroacoustic transducers
Implementation Method 2
at least one internal reflection grating arranged between the two transducers on the path X of the elastic waves
Data Source
AI summary
A surface elastic wave filter has resonant cavities and comprises a composite substrate formed of a base substrate and a piezoelectric upper layer; at least one input electroacoustic transducer and an output electroacoustic transducer, arranged on the upper layer, and at least one internal reflecting structure, arranged between the input electroacoustic transducer and the output electroacoustic transducer. The internal reflecting structure comprises a first structure comprising at least one reflection grating having a first period and a second structure comprising at least one reflection grating having a second period, the first period being greater than the second period.