Directional Coupler with Impedance Mismatch for Broadband Compact Design
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Solution Overview
Problem
Conventional broadband directional couplers are large in size due to their design, which is a disadvantage in compact applications, and they fail to maintain constant coupling attenuation over a broad frequency range like 470 to 950 MHz.
Innovation Solution
A directional coupler with a second coupled line having at least twice the impedance of the first coupled line, and a resistor connected in series either in the forward or backward path, along with an LC-element and grounded resistor, to achieve constant coupling attenuation over a broad frequency range with minimized dimensions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional broadband directional coupler design is used, then coupling attenuation is achieved, but the device dimensions become large
Solution Approach 1:
The patent changes the impedance parameter of the coupled lines, specifically using a second coupled line with impedance at least twice that of the first coupled line. This parameter change enables broadband coupling attenuation with significantly reduced device dimensions compared to conventional designs.
Solution Approach 2:
The patent introduces different impedance characteristics at different locations in the coupled line structure. The second coupled line has locally higher impedance (at least twice) compared to the first coupled line, creating localized impedance transformation that achieves broadband coupling in a compact area.
2Loss of energy
If conventional directional coupler design is used, then coupling is achieved, but the coupling factor varies over frequency range
Solution Approach 1:
The patent employs impedance parameter changes across the coupled lines to achieve frequency-independent coupling. The second coupled line's impedance is at least twice that of the first, and this parameter relationship maintains constant coupling attenuation across the broad frequency range from 470 to 950 MHz.
Solution Approach 2:
The patent creates a composite transmission line structure with two coupled lines having different impedance characteristics. This composite structure combines the first coupled line with standard impedance and the second coupled line with at least twice the impedance, achieving broadband constant coupling that neither line could achieve alone.
3Loss of energy
If impedance transformation is used, then coupling attenuation is improved, but device complexity increases
Solution Approach 1:
The patent achieves impedance transformation by simply changing the characteristic impedance of the second coupled line to be at least twice that of the first coupled line. This parameter-based approach avoids complex transformation circuits while achieving the desired coupling attenuation and broadband performance.
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 results in a directional coupler that is significantly smaller than conventional ones, maintaining a nearly constant coupling factor from 470 to 950 MHz, and when used in power splitters, it provides high decoupling attenuations and lower energy losses, enabling efficient energy utilization for additional receivers.
Implementation Method 1
the second coupled line having a higher line impedance than the first coupled line, at least two times higher, and in that a resistor is connected in series either in the forward path or in the backward path
Implementation Method 2
use a lossy resistance matching to transform it to the output impedance
Data Source
Figure 1~4
Figure 5~6
Figure 7~8
AI summary
Directional coupler (1), comprising at least two coupled lines (2,3) and at least three ports (P1, P2, P3), the first coupled line (1) having at least two ports, an input port (P1) and an output port (P2), the second coupled line (3) having a forward path (4) and a backward path (5) joined together at a third port, the coupled port (P3), and forming a loop. In order to achieve a constant coupling attenuation over a broad frequency band and to minimize the dimensions the second coupled line (3) has a higher line impedance than the first coupled line (2), at least two times higher, and a coupling resistor (6) is connected in series either in the forward path (4) or in the backward path (5). In a multichannel power splitter such directional couplers (1) are connected in series.