Directional Coupler Termination Impedance for High Directivity
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Solution Overview
Problem
Conventional directional couplers with single-layer structures on printed circuit boards achieve only low directivity, and achieving high directivity greater than 30dB requires complex structures or individual optimization, while existing methods for increasing directivity are either frequency-dependent or costly.
Innovation Solution
A directional coupler design with a terminating impedance that causes a 180° phase difference between signals reflected at one port and arriving at another, using a combination of ohmic resistance, inductance, and capacitance to achieve high directivity with low production costs and small space requirements, by mismatching the termination and ensuring destructive interference between coupled signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single-layer structure on a printed circuit board is used, then production costs are low and space requirements are small, but directivity is only low
Solution Approach 1:
The patent changes the termination parameters by introducing a specific impedance value (e.g., 25Ω instead of conventional 50Ω) and using reactive components (inductors and capacitors) to adjust the termination impedance. This parameter modification enables high directivity (>30dB) to be achieved with a simple single-layer structure, resolving the contradiction between manufacturing simplicity and directivity performance.
2Manufacturing precision
If conventional termination matching is used, then most applications are satisfied, but directivity greater than 30dB cannot be achieved
Solution Approach 1:
The patent applies local quality by introducing reactive components (inductors and capacitors) at specific locations (the termination points) of the directional coupler. This localized modification of termination properties enables high directivity without requiring complex overall structure changes, thus achieving >30dB directivity while maintaining relatively simple device architecture.
3Manufacturing precision
If targeted mismatching of insulation connection is used, then directivity is increased, but frequency selectivity increases and production costs increase
Solution Approach 1:
The patent uses a standardized termination design with specific impedance values and reactive component configurations that can be replicated across different frequency applications. By establishing a universal termination scheme (e.g., 25Ω with specific L/C values), the solution achieves high directivity without being tightly coupled to specific frequency requirements, thereby reducing frequency selectivity and improving adaptability.
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 achieves very high directivity with low frequency selectivity and minimal space requirements, while maintaining low production costs, by ensuring that signal reflections and couplings are phase-shifted to achieve destructive interference, thereby enhancing the directional quality of the coupler.
Implementation Method 1
The terminating impedance is dimensioned in such a way that it causes a phase difference of 180° between the signal reflected at the fourth connection and the signal present at the third connection
Implementation Method 2
The signal reflected at the fourth connection and a signal present at the third connection interfere at least partially destructively
Implementation Method 3
The terminating impedance is dimensioned in such a way that it causes a targeted mismatch of the fourth port and a reflection of a portion of a signal arriving at the fourth port
Data Source
Figure 1~2
AI summary
The coupler (30) has a first connection (10) for coupling a signal to a second connection (13) with high attenuation, and a third connection (11) for coupling the signal to the second connection with small attenuation. The second connection is connected with a terminating impedance (20). The impedance is dimensioned such that the impedance causes a target error adjustment of the second connection and reflection of portion of the signal at the second connection. The signal applied to the connection and the signal reflected at the connection are interfered in a partially destructive manner.