Directional Coupler Matching Circuit for Wideband Isolation
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Solution Overview
Problem
Conventional directional couplers suffer from insufficient isolation and return loss in frequency bands not lower than the cut-off frequency of the low-pass filter, limiting their usability to a specific frequency range and making it difficult to provide a wideband capable directional coupler for applications like LTE-Advanced with Carrier Aggregation.
Innovation Solution
A directional coupler design incorporating a matching circuit with a first path including a first inductor and a second path with a capacitor and inductor in series, allowing high frequency signals to pass through over a wider frequency band by varying the phase difference between signal paths, thereby suppressing coupling changes with frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a low-pass filter is used in the subline to flatten coupling response, then coupling flatness is improved, but isolation deteriorates in frequency bands not lower than the cut-off frequency
Solution Approach 1:
The subline is divided into a first subline and a second subline with different electrical characteristics. The first subline includes a low-pass filter for flattening coupling response at lower frequencies, while the second subline provides alternative signal paths at higher frequencies, segmenting the frequency handling responsibilities to resolve the contradiction between coupling flatness and isolation.
Solution Approach 2:
The invention introduces a third dimension by adding a second subline parallel to the first subline, creating multiple signal paths. This dimensional expansion allows the system to handle different frequency ranges through different paths, improving isolation in high frequency bands while maintaining coupling flatness through the low-pass filter in the first subline.
2Adaptability or versatility
If the coupling port is connected to multiple frequency bands, then adaptability is improved, but isolation deteriorates due to signal reflection
Solution Approach 1:
A matching circuit is introduced as an intermediary between the coupling port and the sublines. This matching circuit includes impedance matching elements that mediate between different frequency bands, reducing signal reflection and improving isolation while enabling the coupling port to handle multiple frequency bands simultaneously.
Solution Approach 2:
The directional coupler design achieves multi-functionality by configuring the sublines and matching circuit to handle multiple frequency bands through a single coupling port. The first and second sublines work together to provide universal operation across different frequency ranges used in LTE-Advanced carrier aggregation.
3Device complexity
If a single subline configuration is used, then device complexity is reduced, but coupling flatness deteriorates across wide frequency ranges
Solution Approach 1:
The subline is segmented into first and second sublines with different electrical characteristics. The first subline includes a low-pass filter for lower frequency handling, while the second subline handles higher frequencies. This segmentation allows each subline to be optimized for specific frequency ranges, achieving coupling flatness across wide frequency bands without excessive 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 solution enables a wideband capable directional coupler with improved isolation and reduced signal reflection across a broader frequency range, making it suitable for multiple frequency bands used in LTE-Advanced systems.
Implementation Method 1
The main line and the subline are configured to be electromagnetically coupled to each other
Implementation Method 2
allowing high frequency signals to pass through over a wider frequency band by varying the phase difference between signal paths
Data Source
AI summary
A directional coupler includes: a main line connecting an input port and an output port; a first subline section and a second subline section each of which is formed of a line configured to be electromagnetically coupled to the main line; and a matching circuit provided between the first subline section and the second subline section. The matching circuit includes a first path connecting the first subline section and the second subline section, and a second path connecting the first path and the ground. The first path includes a first inductor. The second path includes a first capacitor and a second inductor connected in series.