Directional Coupler Resistive Element Parasitic Inductance
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Solution Overview
Problem
Existing transmission line directional couplers face challenges in maintaining high isolation and directivity due to parasitic inductances in the coupling line, which cause phase delays and result in non-zero output at the isolation port, leading to insufficient isolation and directivity.
Innovation Solution
Incorporating resistive elements between the main line and the coupling line, or between the signal input/output ports and the isolation/coupling ports, to cancel the real number component of signals caused by parasitic inductances, thereby reducing the output at the isolation port and improving directivity. Additionally, forming the main line, coupling line, and resistive elements on a semi-insulating substrate using a thin-film process to minimize electrical characteristic variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a transmission line directional coupler uses electric field coupling and magnetic field coupling between main line and coupling line, then coupling function is achieved, but parasitic inductances in the coupling line cause phase delays resulting in non-zero output at the isolation port, leading to insufficient isolation and directivity
Solution Approach 1:
The patent converts the harmful effect of parasitic inductances into a beneficial effect by intentionally introducing resistive elements that generate a compensating signal. The resistive elements create a signal with opposite phase to cancel the unwanted signal component caused by parasitic inductances, thereby transforming the harmful phase delay into an opportunity for active cancellation and achieving high isolation and directivity.
Solution Approach 2:
The patent introduces resistive elements as intermediary components between the main line and coupling line. These resistive elements act as mediators that generate compensating signals to counteract the harmful effects of parasitic inductances. The resistive elements serve as the intermediary mechanism that enables signal cancellation and improves isolation without requiring changes to the fundamental coupling structure.
2Reliability
If resistive elements are added to cancel parasitic inductance effects, then isolation and directivity are improved, but device complexity increases
Solution Approach 1:
The patent merges the resistive elements directly into the coupling line structure, integrating them as part of the existing transmission line rather than adding separate discrete components. This merging approach allows the resistive elements to be formed simultaneously with the coupling line in the same manufacturing process, thereby improving isolation and directivity without significantly increasing device complexity or requiring additional fabrication steps.
3Ease of manufacture
If standard substrate is used for manufacturing, then manufacturing process is simple, but electrical characteristic variations are large
Solution Approach 1:
The patent employs a composite substrate structure consisting of a low-dielectric-loss substrate material combined with a ground layer and metal patterns. This composite material approach reduces electrical characteristic variations and signal losses while maintaining compatibility with standard manufacturing processes. The specific substrate material selection and composition are optimized to minimize dielectric losses and improve electrical performance without requiring complex or specialized manufacturing techniques.
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 resistive elements effectively cancel the negative real number component at the isolation port, achieving nearly zero output and enhanced directivity, while the semi-insulating substrate reduces insertion loss and manufacturing variations, resulting in improved isolation and directivity characteristics.
Implementation Method 1
the main line 21 and the coupling line 22 are coupled to each other with electric field coupling by a distributed capacitance C between both lines
Implementation Method 2
coupled to each other with magnetic field coupling by a mutual inductance M
Data Source
AI summary
The disclosure provides a directional coupler having favorable characteristics even when a parasite inductance is present on a coupling line. The directional coupler includes resistive elements between at least either a signal input port and a coupling port or between a signal output port and an isolation port. The resistive elements can reduce the output from the ISO port and improve directivity.