Directional Coupler With Spiral Electrodes for Compact High Isolation
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Solution Overview
Problem
Conventional directional couplers face challenges in reducing size while achieving high coupling and isolation, with side-edge type couplers struggling to minimize size and broad-side type couplers experiencing high capacitance and low isolation.
Innovation Solution
A directional coupler design featuring inner and outer line electrodes with a spiral or helical shape on a dielectric layer, where currents flow in the same direction, enhancing inductive coupling and reducing capacitive coupling, allowing for high inductance values and compact size with adjustable inductance values through turn adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the length of stripline electrodes is reduced to minimize size, then the size of the directional coupler is reduced, but the coupling performance deteriorates
Solution Approach 1:
The patent applies spiral-shaped stripline electrodes instead of straight lines. This curvature allows the electrodes to achieve a length of at least one-quarter wavelength within a compact area, resolving the contradiction between size reduction and coupling performance maintenance. The spiral configuration enables the electric field to extend over a longer path while occupying minimal space.
Solution Approach 2:
The patent transitions from planar straight-line electrodes to three-dimensional spiral structures. By utilizing the radial and angular dimensions of the spiral configuration, the electrode length is effectively increased without proportionally increasing the overall device footprint, thereby maintaining coupling performance while minimizing size.
2Ease of manufacture
If side-edge coupling is used to simplify structure, then manufacturing is easier, but coupling degree is insufficient
Solution Approach 1:
The spiral configuration transforms the side-edge coupling arrangement into an effective broadside coupling structure. The radial orientation of spiral arms creates strong electric field interaction between adjacent spirals, achieving high coupling degree while preserving the relative simplicity of the side-edge manufacturing process.
3Reliability
If broad-side coupling is used to achieve high coupling, then coupling degree improves, but capacitance increases and isolation decreases
Solution Approach 1:
The spiral geometry creates a unique field distribution where strong coupling occurs through radial electric field interaction, while the periodic structure and ground plane configuration minimize parasitic capacitance. The spiral shape naturally provides electrical isolation between adjacent structures while maintaining coupling efficiency.
Solution Approach 2:
The patent implements different structural characteristics in different regions: the spiral arms are positioned and dimensioned to optimize local coupling zones, while ground planes and spacing are configured to minimize parasitic capacitance in non-coupling regions. This localized optimization achieves high coupling without the harmful effects of excessive capacitance.
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 design achieves high coupling and isolation with a smaller size, allowing the directional coupler to be reduced in length to less than a quarter wavelength, while maintaining high inductance values and minimizing capacitance, thus addressing the limitations of existing couplers.
Implementation Method 1
Corresponding currents are transmitted in the same direction through sections of the inner line electrode and the outer line electrode that are adjacent and parallel to each other
Implementation Method 2
allowing for high inductance values and compact size with adjustable inductance values through turn adjustments
Data Source
AI summary
A directional coupler includes a laminate including a ground electrode substrate, a dielectric substrate that includes line electrodes thereon, a lead-out conductor substrate that includes lead-out conductors of the line electrodes, a ground electrode substrate, and a protection substrate. External electrodes for grounding, external electrodes for a main line, and external electrodes for a subordinate line are provided in the laminate. The inner line electrode and the outer line electrode preferably have a spiral or helical shape, and the corresponding currents are transmitted in the same direction through sections of these line electrodes that are adjacent and substantially parallel to each other.