Bent Quarter-Wavelength Stubs for Band-Pass Filter Area Reduction
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Solution Overview
Problem
Conventional high-order microwave band-pass filters required for WLAN devices near the ISM band are too large to fit in standard motherboards, contradicting the design goals of modern communications devices that emphasize compactness, and fail to meet out-band rejection requirements in the lower frequency part of the pass-band.
Innovation Solution
A second-order band-pass filter design that bends two quarter-wavelength open stubs to form a cross-coupling structure, generating additional transmission zeros, thereby enhancing out-band rejection capability and reducing PCB area by creating a second signal transmission path with a phase difference, allowing for better frequency response control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high-order microwave band-pass filter is used to achieve sufficient out-band rejection capability, then the frequency response characteristic is improved, but the overall length and occupied PCB area increase significantly
Solution Approach 1:
The patent applies curvature by bending the transmission line resonators into arc-shaped structures instead of straight lines. This curvature allows the filter to achieve the required electrical length and frequency response characteristics while occupying significantly less PCB area, resolving the contradiction between out-band rejection capability and physical footprint.
Solution Approach 2:
The patent utilizes the spatial dimension by arranging bent resonators in a compact layout pattern. By transitioning from a one-dimensional linear arrangement to a two-dimensional compact configuration with curved paths, the filter achieves high-order filtering performance without proportionally increasing the occupied area.
2Area of stationary object
If a conventional second-order band-pass filter is used, then the PCB area is reduced, but the out-band rejection capability in the lower frequency part of the pass-band is insufficient
Solution Approach 1:
The patent changes the electrical parameters of the filter by introducing coupling capacitors and adjusting the resonator configurations. These parameter modifications enable a second-order filter to generate additional transmission zeros that provide enhanced out-band rejection capability, matching the performance of high-order filters while maintaining compact dimensions.
Solution Approach 2:
The patent introduces coupling capacitors as intermediary elements between the resonators and signal terminals. These capacitors serve as mediators that create additional signal paths and transmission zeros, enhancing the out-band rejection capability without requiring an increase in the number of resonators or overall filter size.
3Reliability
If the transmission line resonators are bent to form a cross coupling structure, then additional transmission zeros are generated, but the structural complexity increases
Solution Approach 1:
The patent employs asymmetric bending patterns in the transmission line resonators, where adjacent resonators are bent in opposite directions or with different curvature radii. This asymmetric configuration creates the cross coupling structure that generates transmission zeros, while the systematic asymmetry maintains manufacturing feasibility and does not excessively increase structural complexity.
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 filter achieves a steep cut-off frequency response and improved out-band rejection while significantly reducing the occupied PCB area, meeting the compactness and performance demands of modern communications devices.
Implementation Method 1
The first transmission line resonator 23 and the second transmission line resonator 24 are respectively a pair of quarter-wavelength open stubs
Implementation Method 2
The impedance inverter 15 is utilized for providing electrical coupling and impedance matching for the two series resonance circuits
Data Source
AI summary
A second-order band-pass filter for generating at least two transmission zeros includes a first signal terminal, a second signal terminal, a first transmission line resonator, a second transmission line resonator and an impedance inverter. The first transmission line resonator and the second transmission line resonator are symmetric to each other and coupled to the first signal terminal and the second signal terminal, which are formed by bending two quarter-wavelength open stubs and have an open circuit gap between the two terminals. The impedance inverter includes an inductor, a first micro strip line and a second micro strip line. The first micro strip line and the second micro strip line are symmetric to each other, and are coupled to the first signal terminal and the second signal terminal and coupled to a ground through the inductor, respectively.