Ladder Filter Attenuation Pole for Harmonic Suppression
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Solution Overview
Problem
Existing ladder type filters face challenges in downsizing while maintaining effective suppression of harmonic components, as methods like lumped constant LC resonance circuits or distributed constant transmission lines can lead to parasitic coupling and degraded filter characteristics when transmission lines are closely spaced.
Innovation Solution
Incorporating series and parallel resonators with a resonator having a lower resonance frequency and an inductor connected in parallel, which forms an attenuation pole to suppress signals outside the pass band, thereby reducing insertion loss and allowing for downsizing without compromising filter performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If transmission lines are made close to each other for downsizing, then the filter size is reduced, but parasitic capacitance or inductance coupling is formed and filter characteristics are degraded
Solution Approach 1:
The filter is divided into multiple resonator units, each with its own series and parallel resonators. This segmentation allows each unit to be optimized independently while maintaining overall filter performance, enabling compact design without parasitic coupling issues
Solution Approach 2:
Different resonators are designed with different resonance frequencies (first resonator: f1, second resonator: f2 where f1 < f2). This local differentiation allows specific frequency components to be suppressed at different locations in the filter, achieving effective harmonic suppression in a compact form
2Object-generated harmful factors
If a resonator with lower resonance frequency is added to suppress harmonic components, then frequency attenuation is improved, but device complexity increases
Solution Approach 1:
The series resonator and parallel resonator are merged into a single resonator unit that performs both series and parallel resonance functions. This integration achieves effective harmonic suppression without proportionally increasing device complexity
Solution Approach 2:
Each resonator unit serves multiple functions: it provides series resonance for fundamental frequency transmission, parallel resonance for harmonic suppression, and contributes to the overall bandpass characteristic. This multi-functionality reduces the need for additional separate components
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 configuration effectively suppresses harmonic components and reduces insertion loss within the pass band, enabling the design of compact filters and duplexers with improved frequency attenuation characteristics.
Implementation Method 1
a resonator connected in series with the series resonators between the input terminal and the output terminal, the resonator having a resonance frequency lower than resonance frequencies of the series resonator
Data Source
AI summary
A ladder type filter includes series resonators S1˜S4 connected in series between an input terminal In and an output terminal Out, parallel resonators P1˜P3 connected in parallel between the input terminal In and the output terminal Out, a resonator RP connected in series with the series resonators S1˜S4 between the input terminal and the output terminal, the resonator RP having a resonance frequency lower than resonance frequencies of the series resonators S1˜S4, and an inductor Lp connected in parallel with the resonator. According to the present ladder filter, signals having frequencies away from the pass band can be suppressed by an attenuation pole formed by the inductor. It is further possible to suppress the insertion loss in the pass band by the resonator.