Direct-Coupled-Stub Filter Layout for Lower Pass-Band Attenuation
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Solution Overview
Problem
Conventional direct-coupled-stub filters (DCSFs) face challenges such as increased power transfer ratio and pass-band attenuation due to dissipation losses, irregular frequency responses at higher frequencies, and unpredictable behavior due to non-punctiform junctions and significant cross dimensions at higher frequencies.
Innovation Solution
The proposed electrical filter structure adjusts the lengths of transmission line portions and stubs to be shorter and longer, respectively, than a quarter of a wavelength, with specific configurations to maintain symmetry and improve filter characteristics without altering the topological structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional DCSF uses quarter-wavelength stubs and transmission lines, then the filter achieves periodic frequency response with multiple pass-bands, but dissipation losses increase power transfer ratio and pass-band attenuation at higher frequencies
Solution Approach 1:
The patent modifies the electrical lengths of transmission line portions and stubs from the conventional quarter-wavelength (λ/4) to deviate from this value. Specifically, the transmission line portions have electrical lengths shorter than λ/4, while stubs have electrical lengths longer than λ/4. This parameter change compensates for dissipation losses and reduces pass-band attenuation, improving energy efficiency while maintaining frequency response regularity.
2Device complexity
If conventional DCSF uses punctiform junctions between stubs and transmission lines, then the filter structure is simple and suitable for printed applications, but junction discontinuities become significant at higher frequencies causing irregular response
Solution Approach 1:
The patent adjusts the electrical lengths of transmission line portions connecting stubs to ports and between stubs. By making these portions shorter than λ/4, the design reduces the impact of junction discontinuities at higher frequencies, improving response predictability while keeping the overall structure simple and suitable for printed circuit implementation.
3Speed
If conventional DCSF operates at higher frequencies, then the filter covers broader frequency ranges, but cross dimensions of stubs and transmission lines become significant compared to wavelength causing irregular and unpredictable response
Solution Approach 1:
The patent uses electrical lengths shorter than quarter-wavelength for transmission line portions, which reduces the physical dimensions of the filter components. This scaling effect helps maintain the validity of the lumped element approximation at higher frequencies, reducing the impact of cross-dimension effects and improving response regularity across broader frequency ranges.
4Stability of the object's composition
If conventional DCSF uses symmetrical configuration with equal electrical lengths, then the filter achieves symmetrical frequency response around pass-band centers, but pass-band additional attenuation increases with frequency from center to edge
Solution Approach 1:
The patent maintains the symmetrical configuration of the filter (with corresponding stubs and transmission lines having matching electrical lengths) to preserve frequency response symmetry. However, it simultaneously changes the absolute electrical length values from the conventional λ/4 to shorter values for transmission lines and longer values for stubs, which compensates for frequency-dependent losses and reduces pass-band attenuation across the bandwidth.
Data Source
AI summary
Embodiments of the present invention provide an electrical filter structure having a direct-coupled-stub filter (DCSF). The lengths of the transmission line portions can be arranged such that electrical lengths of the transmission line portions are shorter, by at least 10 percent, than a fourth of a wavelength of a signal having a frequency of a passband center frequency of the electrical filter structure. Moreover, lengths of the stubs can be selected so that the electrical lengths of the stubs are longer, by at least 2%, than a fourth of a wavelength of a signal having a frequency of a passband center frequency of the electrical filter structure. The filter structures of embodiments of the present invention can advantageously improve filter characteristics without changing the topological structure of the filter.