Coupled-Line Rat-Race Coupler for Stable Output Phase Difference
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Solution Overview
Problem
Traditional rat-race couplers experience instability in output phase due to frequency deviations from the central frequency, affecting the performance of RF devices in communication systems.
Innovation Solution
A coupled-line rat-race coupler design with four ports and four coupled-lines, where the output phases of the third and fourth ports change equally with frequency deviations, maintaining a stable phase difference through specific connections and configurations of the coupled-lines.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If traditional microstrip line configuration is used, then the structure is simple, but the output phase becomes unstable when frequency deviates from central frequency
Solution Approach 1:
The patent changes the electrical length parameters of the microstrip lines from the traditional λ/4 and 3λ/4 configuration to specific values (θ1, θ2, θ3, θ4) that are optimized for broader frequency ranges. This parameter optimization allows the coupler to maintain stable output phase across a wider frequency band, resolving the contradiction between structural simplicity and phase stability.
2Reliability
If microstrip line lengths are optimized for broad bandwidth, then frequency stability improves, but the electric length changes cause phase instability
Solution Approach 1:
The patent introduces asymmetric configuration in the coupled-line structure where the even-mode and odd-mode electrical lengths are deliberately made different (θe ≠ θo). This asymmetric design compensates for the phase changes caused by frequency variations, allowing the output phase to remain stable across a broader frequency range while maintaining manufacturing feasibility.
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 coupled-line rat-race coupler ensures stable output phase difference between the third and fourth ports across a range of frequencies, enhancing the stability and performance of RF devices in communication systems.
Implementation Method 1
The first port is connected with the front end of the first line of the first coupled-line, the fourth port is connected with the front end of the first line of the second coupled-line, the third port is connected with the front end of the second line of the first coupled-line, and the second port is connected with the front end of the second line of the second coupled-line
Implementation Method 2
the front end of the first line of the third coupled-line is short circuited with the front end of the second line of the third coupled-line, the back end of the first line of the fourth coupled-line is open circuited
Data Source
AI summary
A coupled-line rat-race coupler includes four ports and four coupled-lines each composed of two metal lines. Two of the ports are respectively connected with the front ends of the two lines of the first coupled-line, and the other two ports are respectively connected with the front ends of the two lines of the second coupled-line. The two lines of the third coupled-line are short circuited and respectively connected with the back end of one line of the first coupled-line on one side and with the back end of one line of the second coupled-line on the other side. In the fourth coupled-line, one line is open at one end and short circuited at the other end with the other line, which is connected with one line of the first coupled-line and one line of the second coupled-line. The coupled-line rat-race coupler is characterized with smooth and stable output phase.