Directional Coupler Impedance Matching and Directivity Control
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Solution Overview
Problem
Existing directional couplers face issues with impedance matching at the coupling port, leading to increased loss in the sub-line and degradation of detection accuracy, as well as the output of unwanted signal components in other frequency bands to the coupling port.
Innovation Solution
Incorporating a variable impedance circuit at the isolation port and a variable filter circuit at the coupling port, which can be adjusted to stabilize directivity and reduce impedance mismatching, thereby eliminating unwanted waves and suppressing detection accuracy degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a variable impedance circuit is connected to the isolation port to adjust impedance, then directivity is improved, but impedance matching at the coupling port deteriorates
Solution Approach 1:
The patent divides the impedance control function into two separate circuits: a variable impedance circuit connected to the isolation port for directivity control, and a variable impedance circuit connected to the coupling port for impedance matching control. This segmentation allows independent optimization of both functions without mutual interference, resolving the contradiction between improving directivity and maintaining impedance matching.
Solution Approach 2:
The patent introduces a variable impedance circuit at the coupling port as an intermediary element to compensate for impedance mismatching caused by the variable impedance circuit at the isolation port. This intermediary circuit adjusts the impedance at the coupling port to maintain proper matching, thereby reducing loss in the sub-line while preserving the directivity improvements.
2Reliability
If a variable impedance circuit is connected to the isolation port to improve directivity, then unwanted signals in opposite direction are suppressed, but unwanted signal components in other frequency bands are outputted to the coupling port
Solution Approach 1:
The patent separates the functions of directivity control and frequency selection into distinct circuits: the variable impedance circuit at the isolation port handles directivity control, while a filter circuit at the coupling port handles frequency-based unwanted signal suppression. This segmentation allows each circuit to specialize in its function without interfering with the other.
Solution Approach 2:
The patent introduces a filter circuit at the coupling port as an intermediary between the sub-line and the output, which selectively removes unwanted signal components in frequency bands other than the detected frequency band. This filter acts as a mediator that allows desired signals to pass while blocking harmful unwanted components, thereby resolving the issue of unwanted signals being outputted.
Data Source
AI summary
A directional coupler (2) includes a main line (11), a sub-line (12), a variable terminator (13), and a variable filter circuit (15). The variable terminator (13) is a variable impedance circuit that terminates one end portion of the sub-line (12). The variable filter circuit (15) is connected to the other end portion of the sub-line (12). The variable filter circuit (15) may include a filter, a bypass path, and a switch which is connected to at least one of the filter and the bypass path.