Broadband Directional Coupler Stripline High Directivity
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Solution Overview
Problem
Conventional directional couplers with single-layer structures on printed circuit boards achieve only low directivity, requiring complex structures or optimization to exceed 30dB directivity, while multi-layer substrates increase complexity and cost.
Innovation Solution
A directional coupler with at least three lines and three connections, using stripline technology on a single substrate with a metallized backside for ground potential, where the third line is electromagnetically coupled to the first and second lines via coupling gaps, allowing for high directivity with a compact design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional single-layer structure on a printed circuit board is used, then the device complexity is low, but the directivity is limited to low values (cannot exceed 30dB)
Solution Approach 1:
The patent introduces a third dimension by adding a metallized backside to the single-layer substrate, creating a stripline configuration. The third line is coupled to the first and second lines via vias that extend through the substrate to the backside metallization, effectively utilizing the Z-dimension to increase coupling area and achieve high directivity (>30dB) without increasing in-plane complexity
Solution Approach 2:
The patent embeds the coupling structure within the substrate itself by using vias to connect the third line to the backside metallization. The vias are positioned within the substrate thickness, nesting the coupling function inside the existing single-layer structure rather than adding external components, thus achieving high directivity without proportionally increasing device footprint or complexity
2Manufacturing precision
If a multi-layer substrate is used to achieve high directivity, then the directivity exceeds 30dB, but the device complexity and manufacturing cost increase
Solution Approach 1:
Instead of using multiple lateral layers, the patent utilizes the vertical dimension by metallizing the backside of a single-layer substrate and using vias to connect to it. This stripline approach achieves high directivity through increased coupling area in the Z-dimension while maintaining single-layer manufacturing simplicity
Solution Approach 2:
The patent extracts the coupling function from complex multi-layer structures and implements it through a simplified single-layer substrate with backside metallization and via connections. By taking out only the essential coupling elements (third line, vias, backside ground) and positioning them optimally, the patent achieves high directivity without the manufacturing complexity of multi-layer substrates
3Manufacturing precision
If the coupling area is increased to achieve high directivity, then the directivity exceeds 30dB, but the space requirements and device dimensions increase
Solution Approach 1:
The patent increases coupling area by extending it into the vertical dimension through vias and backside metallization rather than expanding in the horizontal plane. The coupled lines approach each other closely in the XY-plane and connect through vias to the backside, creating a three-dimensional coupling volume that achieves high directivity within a compact footprint
Solution Approach 2:
The coupling structure is nested within the substrate thickness by using vias to connect the third line to the backside metallization. This vertical nesting increases effective coupling area without proportionally increasing the device footprint, achieving high directivity in a compact configuration
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 enables high directivity with a simple and compact circuit design, allowing for adjustable frequency-dependent directivity by varying line width and coupling gap selection, significantly increasing directivity without increasing complexity or space requirements.
Implementation Method 1
A third line is arranged between the first line and the second line. The third line is electromagnetically coupled to the first line and the second line, whereby the radio frequency signal is transmitted from the first and second lines to the third line
Implementation Method 2
The metallized rear side of the substrate is connected to a reference potential, in particular ground potential
Data Source
Figure 1~2
Figure 3
Figure 4~5
AI summary
A directional coupler for directed transmission of radio-frequency signals has at least three lines (16, 18, 19) and at least three connections (11, 12, 13, 14). Two lines (18, 19) of the three lines (16, 18, 19) are conductively connected at least at their ends. A third line (16) is arranged between the two first lines (18, 19) and is electromagnetically coupled to them. In this case, the radio-frequency signal is transmitted from the third line (16) to the first line (18) and the second line (19). The coupling takes place via a coupling gap.