Directional Coupler with Segmented Sensing Conductors
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Solution Overview
Problem
Conventional directional couplers using quarter-wave length transmission lines suffer from low directivity and narrow frequency range operation, with modest directivity values and large size, due to incomplete cancellation of even and odd waveforms and significant energy transfer from reverse signals.
Innovation Solution
The directional coupler incorporates two sensing conductors, both substantially shorter than a quarter wave, with their head ends connected to each other and the measurement port, and tail ends coupled to the signal ground, allowing equal but oppositely phased coupling signals from reverse signals to cancel out, improving directivity and reducing size and frequency dependency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If quarter-wave length transmission lines are used in the directional coupler, then the coupling signal is generated, but the directivity is low and the frequency range is narrow
Solution Approach 1:
The single quarter-wave transmission line is segmented into two sensing conductors, each substantially shorter than a quarter wave. These segmented conductors are positioned at different locations in the interspace, allowing the coupler to achieve high directivity through differential coupling while maintaining broadband operation across a wide frequency range.
Solution Approach 2:
Different regions of the interspace are utilized by placing sensing conductors at specific locations with different coupling characteristics. The first sensing conductor is positioned to provide strong coupling, while the second is positioned to provide weaker coupling, creating local quality differences that enable high directivity through signal subtraction.
2Measurement precision
If quarter-wave length transmission lines are used, then coupling is achieved, but the device size is large
Solution Approach 1:
The quarter-wave transmission line is divided into multiple shorter sensing conductors (first and second sensing conductors), each substantially shorter than a quarter wave. This segmentation maintains the coupling function while significantly reducing the overall conductor length and device size.
Solution Approach 2:
Instead of extending the conductor length in one dimension to achieve quarter-wave coupling, the invention uses multiple shorter conductors positioned at different locations in the interspace. This dimensional redistribution allows coupling to be achieved through spatial arrangement rather than length alone.
3Device complexity
If single sensing conductor is used, then the structure is simple, but the reverse signal cancellation is incomplete
Solution Approach 1:
The single sensing conductor is segmented into two separate sensing conductors positioned at different locations. This segmentation enables differential measurement where the first sensing conductor picks up both forward and reverse signals, while the second picks up primarily reverse signals, allowing complete cancellation of reverse signals through subtraction.
Solution Approach 2:
The second sensing conductor acts as an intermediary that specifically detects the reverse signal component. By comparing the outputs of both sensing conductors, the reverse signal is eliminated as a harmful factor, leaving only the forward signal for measurement.
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 design achieves high directivity and constant measurement signal level across a large frequency range, with low return loss and simplified, cost-effective tuning, resulting in a compact and efficient directional coupler.
Implementation Method 1
Because of the electromagnetic coupling between it and the first conductor strip, part of the energy fed to the input port transfers to the circuit of the second conductor strip
Implementation Method 2
the sensing conductors are coupled from their tail ends to the signal ground and are designed and located so that coupling signals caused by a reverse signal are substantially equal of their level and oppositely phased at the connecting point of the sensing conductors in order to cancel them out
Data Source
AI summary
A directional coupler with two sensing conductors and a basic coupler and a supplementary coupler corresponding to them. The basic coupler is based on the coupling between a first sensing conductor (421) and the transmission conductor (410), and the supplementary coupler is based on the coupling between a second sensing conductor (422) and the transmission conductor. The sensing conductors are substantially shorter than a quarter wave, because of which the directivity of both the basic and the supplementary coupler is low. The other ends of the sensing conductors are connected to each other and further to the measurement port of the directional coupler. The coupling signals caused by a reverse signal in the connecting point of the sensing conductors are arranged equal by their absolute value but oppositely phased, in which case their sum signal in the measurement port is insignificantly small. For this purpose, for example, the transmission line formed by the first sensing conductor and the ground is terminated with a matching element at its opposite end, and the transmission line formed by the second sensing conductor and the ground is left open at its opposite end. The termination impedances can be adjustable and the directional coupler thus tunable. In this manner, the directivity of the total directional coupler is improved by means of the second sensing conductor. The directional coupler is small-sized, and good directivity is achieved in a very large frequency range.