High-Directivity Directional Coupler with Impedance Discontinuity
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Solution Overview
Problem
Current directional couplers in high-power microwave systems suffer from low directivity, leading to inaccurate power measurements due to insufficient separation of forward and reflected waves, and are not suitable for high-power applications beyond 100W due to substrate arcing and material breakdown risks.
Innovation Solution
A high-directivity directional coupler design featuring a mainline metal segment with equal-width transmission/delay lines and coupling metal segments with gradually changing widths or impedance, allowing for improved phase difference-based voltage cancellation and increased directivity, even at larger stripline distances, thus enabling accurate power measurement in high-power systems up to 5000W.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the distance between coupling lines is increased to reduce substrate loss and improve high-power performance, then the directivity deteriorates due to different odd and even mode phase speeds
Solution Approach 1:
The patent introduces asymmetric impedance transformation structures at the coupling end, where the coupling line width changes abruptly to create impedance discontinuity. This asymmetric design causes reflected waves to have different phase characteristics for odd and even modes, compensating for the phase speed differences that occur when coupling lines are spaced far apart, thereby maintaining high directivity even with increased spacing for high-power applications
Solution Approach 2:
The patent changes the impedance parameters along the coupling line by introducing width variations and discontinuities. Specifically, the coupling line width is modified at certain positions to create impedance transformation zones, which alter the phase and amplitude characteristics of coupled waves. This parameter change enables the system to achieve both large coupling line spacing (for high-power performance) and high directivity (for measurement precision) simultaneously
2Stability of the object's composition
If equal-width coupling lines are used to avoid reflection, then the directivity cannot be improved when coupling lines are spaced far apart due to phase speed differences
Solution Approach 1:
The patent applies local quality by maintaining uniform width (good signal stability) in most sections of the coupling line, while introducing localized width variations and impedance discontinuities at specific positions (the coupling end). These local modifications create the necessary phase compensation effects to improve directivity without disrupting the overall signal stability provided by the equal-width sections
3Adaptability or versatility
If multi-stage series connection is used to increase directional bandwidth, then the coupler size becomes too long and insertion loss increases
Solution Approach 1:
The patent segments the coupling function into distinct zones: a coupling zone with varying width for power transfer, a delay zone with specific length for phase adjustment, and an impedance transformation zone at the end for directivity enhancement. This segmentation allows each zone to perform its specific function efficiently, achieving broad directional bandwidth without requiring multiple long stages, thus reducing overall coupler size and insertion loss
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 design achieves high directivity and expanded directional bandwidth, reducing coupler volume and enhancing measurement accuracy for forward and reflected power, while preventing material breakdown, making it suitable for high-power RF amplifiers and microwave systems.
Implementation Method 1
a small portion of power is drawn by electromagnetic coupling from the mainline to the coupling line for power measurement
Implementation Method 2
uses the mode of alternating arrangement of multi-coupling segments and delay segments to improve directivity, and the principle system utilizes phase delay provided by the delay lines for voltage cancellation
Data Source
AI summary
The high-directivity directional coupler of the present invention allows the coupler to maintain high-directivity when the stripe line distance between the mainline metal segment and at least one coupling metal segment is relatively large, to avoid material breakdown by a strong electric field under high-power operation, and is suitable for accurate power measurement in high-power RF systems.