Microwave Stub Filter Layout for Sharper Low-Pass Selectivity
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Solution Overview
Problem
Conventional direct-coupled-stub microwave filters face issues such as dissipation losses, irregular frequency responses, and poor predictability at higher frequencies due to physical realizable stubs and transmission lines, leading to suboptimal power transfer ratios and selectivity, especially on the low-pass side.
Innovation Solution
The proposed electrical filter structure features pairs of open and short-circuited stubs coupled in parallel to transmission lines, with specific length adjustments to achieve equal electrical lengths within a tolerance, and transmission line lengths shorter than a quarter wavelength to enhance selectivity, particularly on the low-pass side.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional direct-coupled-stub filters are used with physically realizable stubs and transmission lines, then the filter structure is simple and easy to manufacture, but dissipation losses increase and power transfer ratio decreases at higher frequencies
Solution Approach 1:
The patent modifies the electrical lengths of transmission lines and stubs to specific values (transmission lines shorter than λ/4, stubs longer than λ/4) to optimize filter performance. This parameter adjustment reduces dissipation losses and improves power transfer ratio while maintaining the conventional filter topology for ease of manufacture.
2Device complexity
If conventional direct-coupled-stub filters are used with standard transmission line lengths, then the design is straightforward, but frequency response becomes irregular and unpredictable at higher frequencies
Solution Approach 1:
The patent specifies precise electrical length parameters for transmission lines (shorter than quarter wavelength) and stubs (longer than quarter wavelength) to ensure regular and predictable frequency responses at higher frequencies, while maintaining relatively simple filter topology.
3Volume of moving object
If conventional direct-coupled-stub filters are used, then the filter structure is compact, but selectivity deteriorates especially on the low-pass side
Solution Approach 1:
The patent optimizes the electrical lengths of transmission lines and stubs to enhance filter selectivity, particularly on the low-pass side, while preserving the compact filter structure through the direct-coupled-stub topology.
4Device complexity
If stubs and transmission lines are punctiformly joined as in conventional filters, then the connection is simple, but discontinuities become significant at higher frequencies causing response irregularities
Solution Approach 1:
The patent adjusts the electrical lengths of transmission lines and stubs to compensate for discontinuity effects at higher frequencies, maintaining regular frequency responses while keeping the connection structure relatively simple.
Data Source
AI summary
An electrical filter structure for forwarding an electrical signal from a first port, e.g. P1, to a second port, e.g. P2, in a frequency selective manner, wherein the filter is a microwave filter, the electrical filter structure comprising: a plurality of pairs of an open stub and a short-circuited stub coupled electrically in parallel to a transmission line comprising a plurality of transmission line portions at a plurality of respective junctions between adjacent transmission line portions, e.g. Cross junction; and wherein the first port is connected with a first of the junctions having a first pair comprising a first open stub and a first short-circuited stub; wherein the second port is connected with a last of the junctions having a last pair comprising a last open stub and a last short-circuited stub; wherein lengths of the pair of the open stub and the short-circuited stub coupled to a same of the junctions are chosen such that electrical lengths of the open stub and short-circuited stub of the respective pairs are equal within a tolerance of +/−10%.