Directional Coupler with Segmented Low Pass Filters
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Solution Overview
Problem
Existing directional couplers face challenges in achieving a flat coupling curve over a wide frequency band while minimizing coupling in unnecessary frequency bands, with previous solutions either increasing device size or causing signal leakage.
Innovation Solution
A directional coupler design featuring multiple stages of low pass filters between the coupling terminal and sub lines, with distinct cutoff frequencies and additional inductors and capacitors, along with a multilayer body structure to reduce signal leakage and enhance attenuation in unnecessary frequency bands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a low pass filter is inserted between the coupling terminal and the sub line, then coupling in unnecessary frequency bands is reduced, but the device size is remarkably increased
Solution Approach 1:
The sub line is divided into multiple segments (first sub line, second sub line, third sub line) with low pass filters inserted between them. This segmentation allows the filtering function to be distributed across multiple smaller sections rather than requiring one large filter, thereby reducing coupling in unnecessary frequency bands while controlling device size.
Solution Approach 2:
Different sections of the sub line are equipped with low pass filters having different cutoff frequencies. The first low pass filter has a first cutoff frequency, the second low pass filter has a second cutoff frequency lower than the first, and the third low pass filter has a third cutoff frequency lower than the second. This local differentiation optimizes filtering performance at different locations while maintaining compact dimensions.
2Measurement precision
If multiple low pass filters with different cutoff frequencies are distributed along the sub line, then a flat coupling curve over wide frequency band is achieved, but device complexity increases
Solution Approach 1:
The filtering function is segmented into multiple low pass filters positioned at different locations along the sub line. Each filter handles a specific frequency range, and their combined effect produces a flat coupling curve over a wide frequency band while distributing the complexity across manageable sections.
Solution Approach 2:
The cutoff frequencies of the low pass filters are progressively changed (first cutoff frequency > second cutoff frequency > third cutoff frequency) to create overlapping frequency responses. This parameter variation ensures flat coupling characteristics across a broad frequency range while maintaining a systematic rather than arbitrary structure.
3Object-affected harmful factors
If low pass filters are inserted to reduce high-frequency coupling, then coupling in unnecessary frequency bands is reduced, but signal leakage occurs
Solution Approach 1:
Different sections of the sub line have low pass filters with locally optimized cutoff frequencies. This local quality differentiation ensures that signal attenuation is achieved at the appropriate locations and frequency ranges, preventing signal leakage while effectively reducing coupling in unnecessary frequency bands.
Solution Approach 2:
The cutoff frequencies of the low pass filters are progressively changed to create a cascading filtering effect. This parameter progression ensures that signals are attenuated at multiple frequency thresholds, preventing signal leakage while maintaining effective suppression of high-frequency coupling.
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 a flat coupling curve over a wide frequency band with significant reduction in unnecessary coupling, preventing signal leakage and improving overall directional coupler characteristics.
Implementation Method 1
a first low pass filter; a second low pass filter
Implementation Method 2
a first inductor, at least a second inductor
Implementation Method 3
at least a first capacitor, at least a second capacitor, and at least a third capacitor
Data Source
AI summary
A directional coupler includes an input terminal, an output terminal, a coupling terminal, a termination terminal, a first ground terminal, second ground terminals, a main line, a first sub line, and a second sub line. A first low pass filter is included between the coupling terminal and the first sub line. A second low pass filter is included between the first sub line and the second sub line. The first low pass filter is electrically connected to the first ground terminal, and the second low pass filter is electrically connected to the second ground terminals.