Directional Coupler With Low Pass Filter for Constant Coupling
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Solution Overview
Problem
Conventional directional couplers exhibit a frequency-dependent coupling characteristic, leading to varying signal power output when input signals of different frequencies are applied, necessitating additional signal correction by ICs.
Innovation Solution
Incorporating a low pass filter with a capacitor and coil configuration between the main and sub-lines, which attenuates signal power with increasing frequency, thereby maintaining a relatively constant coupling characteristic across the frequency band.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional directional coupler structure is used, then the device is simple in structure, but the coupling characteristic varies with frequency
Solution Approach 1:
A low-pass filter is introduced as an intermediary component between the main line and sub line to compensate for frequency-dependent coupling variations. The filter acts as a mediator that adjusts the signal characteristics to maintain consistent coupling across different frequencies, resolving the contradiction between structural simplicity and coupling consistency.
Solution Approach 2:
The invention changes the electrical parameters of the directional coupler by incorporating a low-pass filter with specific cutoff frequency characteristics. This parameter modification allows the coupling characteristic to remain constant across a frequency band, transforming the frequency-dependent behavior into frequency-independent operation.
2Power
If the frequency of the input signal increases, then the coupling degree increases, but the coupling characteristic becomes non-constant
Solution Approach 1:
The invention converts the harmful frequency-dependent coupling variation into a beneficial constant coupling characteristic. By introducing the low-pass filter, the natural increase in coupling degree with frequency is compensated, transforming the problematic frequency dependence into a stable coupling performance across the operating band.
3Device complexity
If no low pass filter is used, then the device complexity is low, but additional IC correction is required
Solution Approach 1:
The low-pass filter function is merged with the directional coupler structure, integrating frequency compensation directly into the coupler. This combination eliminates the need for separate IC correction circuits, reducing overall system complexity while improving signal processing efficiency by providing inherent frequency compensation.
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 ensures a consistent coupling characteristic, reducing the need for frequency-based signal correction and minimizing isolation characteristic attenuation, thus stabilizing signal power output across varying frequencies.
Implementation Method 1
Incorporating a low pass filter with a capacitor and coil configuration between the main and sub-lines, which attenuates signal power with increasing frequency
Implementation Method 2
a low pass filter with a capacitor and coil configuration
Implementation Method 3
a low pass filter with a capacitor and coil configuration
Implementation Method 4
The main line and the sub-line are electromagnetically coupled with each other
Data Source
Figure 1~3
Figure 4~5
Figure 6
AI summary
Provided is a directional coupler in which the degree of coupling is closer to be being constant. A directional coupler (10a) is to be used in a predetermined frequency band. A main line (M) is provided between an outer electrode (14a) and an outer electrode (14b). A sub-line (S) is provided between an outer electrode (14c) and an outer electrode (14d) and is electromagnetically coupled with the main line (M). A low pass filter (LPF1) is provided between the outer electrode (14c) and the sub-line (S) and has a characteristic that attenuation increases with increasing frequency in a predetermined frequency band.