Directional Coupler Impedance Conversion Sections Directivity
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Solution Overview
Problem
Directional couplers with load circuits at the isolation port improve directivity for input signals but hinder the detection of reflecting signals, and adjusting the configuration to detect reflecting signals is challenging due to power reflection issues at both the isolation and coupling ports.
Innovation Solution
Incorporating first and second impedance conversion sections at both ends of the secondary line, allowing for independent adjustment of the apparent load to equalize current amplitudes from electric-field and magnetic-field coupling, thereby improving directivity by setting impedances viewed from the secondary line side to specific ratios relative to port-side impedances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a load circuit is connected at the isolation port to improve directivity, then directivity for input signals is improved, but the detection of reflecting signals from the signal output port is hindered
Solution Approach 1:
The patent divides the isolation port function into two separate ports: a first isolation port connected to a first load circuit for improving directivity of input signals, and a second isolation port for detecting reflecting signals. This segmentation allows both functions to operate independently without mutual interference, resolving the contradiction between directivity improvement and signal detection capability.
Solution Approach 2:
The patent introduces an impedance conversion section as an intermediary component between the secondary line and the isolation ports. This impedance conversion section transforms the impedance to match between the transmission line and load circuits, enabling both directivity improvement and reflecting signal detection to function simultaneously by mediating the electrical characteristics between different circuit portions.
2Ease of manufacture
If the magnetic-field coupling coefficient is less than one due to parasitic inductance, then the directional coupler becomes more practical, but complete cancellation of coupling signals at the isolation port cannot be achieved
Solution Approach 1:
The patent changes the impedance parameter at the isolation ports through impedance conversion sections. By transforming the impedance to an optimal value, the system compensates for the imperfect magnetic-field coupling coefficient caused by parasitic inductance, enabling effective signal cancellation at the first isolation port while maintaining practical manufacturability.
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
This configuration allows for enhanced directivity by ensuring that currents from both coupling mechanisms are equal in amplitude, effectively canceling each other out at the isolation or coupling ports, thus enabling the detection of both input and output signals with improved directivity.
Implementation Method 1
The main line 121 and the secondary line 122 are electrically coupled to each other through a distributed capacitance (coupling capacitance) C between two lines
Implementation Method 2
magnetically coupled to each other through a mutual inductance M
Data Source
Figure 1~2
Figure 3
Figure 4(A)~4(C)
AI summary
Achieve favorable directivity in directional coupler even with low magnetic-field coupling coefficient. A directional coupler (1) includes a main line (2), a secondary line (3), and impedance conversion sections (4, 5). The main line (2) is connected between a signal input port (RFin) and a signal output port (RFout). The secondary line (3) is coupled to the main line (2) through coupling capacitance and mutual inductance. The impedance conversion sections (4, 5) are connected between the secondary line (3) and a coupling port (CPL) or an isolation port (ISO), and the impedance viewed from the secondary line (3) differs from the impedance viewed from a port side while both impedances viewed from the secondary line (3) are equal.