SAW Transversal Filter Weighting for Triple Transit Suppression
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing RSPUDT transversal filters face challenges in achieving high out-of-band rejection and low insertion loss, particularly for large band filters, due to limitations in suppressing triple transit signals and maintaining a sharp transition between passband and rejection band.
Innovation Solution
The solution involves a transversal filter design with a piezoelectric substrate and distributed acoustic tracks, where input and output transducers are divided into sub-transducers with distinct excitation strengths to form main and tail lobes, allowing for precise modeling of the transfer function and reduced insertion loss through apodization avoidance and strategic electrical connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If apodized transducer without reflectors is used, then insertion loss is reduced, but triple transit signals are not sufficiently suppressed
Solution Approach 1:
The transducer is divided into multiple segments with different excitation strengths (main lobe and tail lobes). The main lobe provides strong excitation for low insertion loss, while the tail lobes with reduced excitation strength suppress triple transit signals. This segmentation allows simultaneous optimization of both insertion loss and triple transit suppression.
Solution Approach 2:
Different regions of the transducer are assigned different excitation characteristics. The main lobe region has high excitation strength for efficient energy transfer, while the tail lobe regions have reduced excitation strength to suppress unwanted reflections. This local differentiation resolves the contradiction between low insertion loss and triple transit suppression.
2Object-generated harmful factors
If serial connection of partial transducers is used to approximate fan-shaped weighting, then triple transit suppression is improved, but insertion loss increases and performance degrades for very long transducers
Solution Approach 1:
The invention uses dynamic excitation control where the excitation strength varies continuously along the transducer length through main lobe and tail lobe configuration. This dynamic approach allows optimal suppression of triple transit signals while maintaining low insertion loss, overcoming the limitations of static serial connections of partial transducers.
3Object-generated harmful factors
If highly reflective structures (acoustic cavities) are used, then out-of-band rejection is improved, but the filter size increases and is not suitable for large band filters
Solution Approach 1:
The invention replaces traditional mechanical acoustic cavity structures with an electrical field-based solution using distributed excitation with main and tail lobes. This substitution achieves high out-of-band rejection through electromagnetic field control rather than physical acoustic reflections, significantly reducing filter size while maintaining performance for large band filters.
4Ease of manufacture
If discrete source distribution is used in RSPUDT structure, then manufacturing is simplified, but precision of transfer function modeling is reduced
Solution Approach 1:
The invention uses a discrete distribution of sources that provides sufficient precision for transfer function modeling without requiring continuous distribution. The main lobe and tail lobe configuration with specific excitation strengths achieves the necessary modeling precision while maintaining the simplicity of discrete source implementation, resolving the contradiction between manufacturing ease and modeling precision.
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 achieves a high level of out-of-band rejection and low insertion loss, enabling filters with improved rejection performance far from the passband, with specific embodiments demonstrating relative bandwidths over 3%, transition bandwidths below 0.1%, and insertion losses less than 10 dB.
Implementation Method 1
a piezoelectric substrate and at least one acoustic track formed on the substrate. At least one SAW input transducer and at least one SAW output transducer are arranged in each track
Implementation Method 2
at least one acoustic track formed on the substrate. At least one SAW input transducer and at least one SAW output transducer are arranged in each track
Implementation Method 3
Suppression of triple transit signals and a high out-of-band rejection is a question of sufficient resonant structures and the length of the transducer
Data Source
AI summary
The filter includes at least one acoustic track formed on a piezoelectric substrate. At least one SAW input transducer and at least one SAW output transducer are arranged in each track. Each track has a RSPUDT structure and thus a distributed excitation. The excitation function includes sources arranged in a main lobe and a tail function including at least one tail lobe. A fine and precise approximation to the desired continuous excitation function is obtained by decreasing the excitation strength in the tail function by a factor of at least 2.