Directional Coupler Series Capacitor Parasitic Inductance
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Solution Overview
Problem
Directional couplers face challenges in maintaining good isolation characteristics and directivity due to parasitic inductance, which often results in increased device size and degradation of insertion loss.
Innovation Solution
Incorporating a series capacitor with a capacitance that resonates with parasitic inductances in the directional coupler, specifically connected to either the signal output port or the coupling port, to improve isolation and directivity while minimizing device size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a series capacitor is connected to both signal output port and coupling port to compensate parasitic inductance, then isolation and directivity are improved, but device size increases
Solution Approach 1:
The patent extracts the series capacitor from one of the two connection points (either signal output port or coupling port) while maintaining the essential function of parasitic inductance compensation. This selective connection approach achieves the required isolation and directivity improvement without requiring capacitors at both ports, thereby reducing device size.
Solution Approach 2:
The patent optimizes the connection configuration by changing the parameter of capacitor placement from 'both ports' to 'single port'. This parameter change maintains the electrical function of compensating parasitic inductance while reducing the physical footprint of the device.
2Area of stationary object
If parasitic inductance is present in the directional coupler, then device size can be reduced, but isolation and directivity characteristics degrade
Solution Approach 1:
The patent converts the harmful effect of parasitic inductance into a beneficial function by introducing a series capacitor that resonates with the parasitic inductance at the operating frequency. This resonance relationship transforms the parasitic element from a source of performance degradation into a mechanism for achieving isolation and directivity improvement without requiring additional space.
Solution Approach 2:
The series capacitor acts as an intermediary element that mediates between the parasitic inductance and the signal transmission. By introducing this intermediate component, the patent enables the parasitic inductance to contribute positively to isolation and directivity rather than degrading performance.
3Reliability
If a series capacitor is added to resonate with parasitic inductance, then isolation characteristics improve, but insertion loss increases
Solution Approach 1:
The patent optimizes the capacitance value of the series capacitor to achieve resonance with parasitic inductance at the operating frequency. By carefully selecting this parameter, the capacitor compensates for parasitic effects and improves isolation characteristics while minimizing the impact on insertion loss through optimal impedance matching.
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 effectively enhances isolation and directivity characteristics, suppressing the increase in device size and maintaining low insertion loss, even in the presence of parasitic inductance, by using a smaller series capacitor that resonates with existing parasitic inductances.
Implementation Method 1
Incorporating a series capacitor with a capacitance that resonates with parasitic inductances in the directional coupler
Implementation Method 2
The main line 121 and the sub line 122 are coupled to each other through electric field coupling due to distributed capacitances C between the two lines
Implementation Method 3
at the same time coupled to each other through magnetic field coupling due to the mutual inductance M
Data Source
AI summary
In a directional coupler, even when parasitic inductance exists, an increase in device size can be suppressed while obtaining good isolation characteristics. A transmission line type directional coupler includes a main line and a sub line that is coupled to the main line through electric field coupling and magnetic field coupling. The main line includes a signal input port and a signal output port, and the sub line includes a coupling port and an isolation port. A series capacitor is connected to only one of the signal output port and the coupling port.