Embedded Resonator Sharpens Low Pass Filter Cut-Off
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Solution Overview
Problem
Existing microwave low-pass filters (LPFs) suffer from spurious signal suppression limitations, including pass-band attenuation and non-sharp cut-off slopes, which affect communication quality and spectrum usability, with existing solutions increasing complexity and cost or requiring material changes.
Innovation Solution
An embedded notch frequency resonator filter is integrated into a stepped-impedance resonator (SIR) LPF structure, using a dielectric spacer and inner conductor to form a capacitive couple with an LC resonator, allowing for adjustable notch frequency and maximum attenuation without altering the center frequency, and enabling cascading for wider spurious mode rejection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional SIR LPF structure is used, then the filter is simple to manufacture, but spurious signal suppression is insufficient with non-sharp cut-off slopes
Solution Approach 1:
The patent embeds an additional resonator structure within the existing SIR LPF configuration. The embedded resonator is positioned inside the filter housing, utilizing the same physical space. This nesting approach enhances spurious signal suppression capability by adding transmission zeros near the cut-off frequency without requiring additional external components or increasing the overall filter footprint, thus improving manufacturing precision while maintaining reasonable device complexity
Solution Approach 2:
The patent introduces an intermediate embedded resonator that acts as a mediator between the input and output transmission lines. This resonator couples to both lines and creates transmission zeros at specific frequencies, effectively suppressing spurious signals. The embedded resonator serves as an intermediary element that modifies the filter's frequency response without fundamentally changing the basic SIR LPF structure, thereby improving spurious signal suppression while keeping the design relatively simple
2Manufacturing precision
If mask filter is added to suppress spurious signals, then spurious suppression improves, but pass-band insertion loss increases and complexity increases
Solution Approach 1:
The patent applies local quality by designing the embedded resonator with specific impedance characteristics that are optimized for spurious signal suppression at particular frequency ranges. The resonator's impedance is tailored to create transmission zeros only where needed (near the cut-off frequency and spurious bands) while maintaining good matching in the pass-band. This localized optimization allows effective spurious suppression without introducing excessive insertion loss across the entire frequency spectrum
Solution Approach 2:
The patent utilizes the dynamic coupling between the embedded resonator and the main SIR LPF structure. By adjusting the coupling coefficients and resonant frequencies of the embedded resonator, the filter can dynamically suppress spurious signals at specific frequencies while allowing pass-band signals to pass with minimal loss. The embedded resonator's ability to be tuned and its frequency-selective coupling enable dynamic control over which frequencies are suppressed, improving spurious suppression without permanently increasing pass-band insertion loss
3Manufacturing precision
If multiple resonator sections are added to improve cut-off slope, then frequency response improves, but device complexity and cost increase
Solution Approach 1:
The patent extracts the spurious signal suppression function from the main filter structure by separating it into a distinct embedded resonator component. Instead of increasing the number of main resonator sections, the suppression function is extracted and implemented by the embedded resonator alone. This extraction allows the main SIR LPF structure to remain relatively simple while achieving improved cut-off slope and spurious suppression through the embedded element's specific design
Solution Approach 2:
The embedded resonator serves multiple functions simultaneously: it improves the cut-off slope, suppresses spurious signals, and maintains a compact form factor. By designing the embedded resonator with multi-functionality, the patent achieves enhanced frequency response characteristics without proportionally increasing device complexity. The single embedded resonator structure performs what would otherwise require multiple additional resonator sections, thereby improving cut-off slope while keeping the overall device complexity manageable
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 solution provides enhanced spurious suppression with a sharp rejection profile near the operating band and a wide spurious suppression window, improving communication quality and reducing complexity and cost by maintaining a simple, easy-to-manufacture filter design.
Implementation Method 1
form a capacitive couple with an LC resonator
Implementation Method 2
form a capacitive couple with an LC resonator
Implementation Method 3
embedded notch frequency resonator filter
Data Source
AI summary
An embedded resonator sharpens the frequency characteristics of a coaxial low pass filter. The resonator introduces finite transmission zeros to the response of the low pass filter, thereby suppressing spurious modes occurring just above the operating frequency. Two parameters are used to tune the operation of the embedded resonator. The length of an insert into the filter's transmission line substantially controls the resonant frequency, and the gap width substantially controls the coupling of the embedded resonator to the low pass filter.