Layered Bandpass Filter Spurious Peak Control
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Solution Overview
Problem
Existing layered bandpass filters face issues with spurious peaks occurring at frequencies higher than the passband due to the coupling path forming capacitive coupling between non-adjacent resonators, which degrades attenuation characteristics and fails to meet the required attenuation levels in specific frequency bands.
Innovation Solution
A layered bandpass filter design with multiple coupling paths in parallel, each comprising a capacitor and an inductor connected in series, allowing for adjustable capacitance and inductance to control the resonant frequency of the coupling paths, thereby shifting the spurious peak to a higher frequency without impairing the attenuation pole formation at lower frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a coupling path including a capacitor is provided to form capacitive coupling between two non-adjacent resonators, then attenuation characteristics at frequencies lower than the passband are improved, but spurious peaks occur at frequencies higher than the passband frequencies
Solution Approach 1:
The patent introduces an inductor into the coupling path to change the electrical parameters of the circuit. By adjusting the inductance value and capacitance value, the resonant frequency of the coupling path can be controlled to shift spurious peaks to frequencies above the stopband region, while maintaining the attenuation pole formation at frequencies below the passband. This parameter adjustment resolves the contradiction by transforming the harmful spurious peaks into a controllable feature.
Solution Approach 2:
The inductor acts as an intermediary element in the coupling path between non-adjacent resonators. It mediates the capacitive coupling effect by introducing inductive reactance that counterbalances the capacitive effect at certain frequencies, thereby suppressing spurious peak formation in the stopband while preserving the desired attenuation characteristics.
2Object-generated harmful factors
If the capacitance or inductance is reduced to shift the spurious peak frequency higher, then the spurious peak moves outside the required attenuation band, but the attenuation pole formation at lower frequencies is impaired
Solution Approach 1:
The patent optimizes the specific values of capacitance and inductance in the coupling path to achieve a balance. By carefully selecting these parameters, the resonant frequency of the coupling path is positioned such that spurious peaks occur above the stopband while attenuation poles are properly formed below the passband. This precise parameter control resolves the contradiction between shifting spurious peaks and maintaining attenuation characteristics.
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 controls the frequency of spurious peaks to be outside the passband, ensuring the bandpass filter achieves the desired attenuation characteristics across the required frequency bands, preventing degradation of performance.
Implementation Method 1
The coupling path includes a capacitor
Implementation Method 2
The coupling path includes an inductor connected in series
Implementation Method 3
The coupling path is considered as a series resonant circuit formed by the capacitor and the inductor
Implementation Method 4
two adjacent resonators are electromagnetically coupled to each other. The electromagnetic coupling includes inductive coupling and capacitive coupling
Data Source
AI summary
A bandpass filter includes three resonators of which adjacent two are electromagnetically coupled to each other, and two coupling paths connected in parallel for forming capacitive coupling between non-adjacent two of the resonators. Each of the two coupling paths includes at least one capacitor and an inductor connected in series. The two coupling paths function to form an attenuation pole at a frequency lower than the passband frequencies in the pass attenuation characteristics of the bandpass filter.