Tapered Laminated Waveguide Connection for High-Frequency Signal Integrity
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Solution Overview
Problem
Existing high-frequency transmission line connection structures between microstrip lines and laminated waveguides suffer from poor frequency characteristics and increased conversion loss due to electromagnetic wave leakage and mode conversion issues, particularly at high frequencies like 76.5 GHz.
Innovation Solution
A high-frequency transmission line connection structure is developed, featuring a laminated waveguide configuration with varying dielectric layer thickness and via-hole conductors to match impedance and reduce leakage, comprising a sub-line part, main-line part, conversion part, and common line part, with specific dimensions and arrangements to optimize signal propagation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a slot is formed in a ground conductor to couple the microstrip line with the laminated waveguide, then electromagnetic coupling is achieved, but the frequency bandwidth where reflected waves have -20 dB or lower is only 3.7 GHz, resulting in poor frequency characteristics
Solution Approach 1:
A tapered conversion structure is introduced as an intermediary between the microstrip line and the laminated waveguide. This conversion structure includes a tapered conductor that gradually transitions from the microstrip width to the waveguide width, serving as a mediator that facilitates smooth mode conversion and reduces reflections across a wider frequency bandwidth.
Solution Approach 2:
The conductor width in the conversion structure is varied continuously through a taper profile. By changing the geometric parameter (width) gradually from the microstrip line width to the waveguide width, the impedance transitions smoothly, improving frequency characteristics and expanding the usable bandwidth beyond the 3.7 GHz limitation of the slot coupling method.
2Reliability
If the strip conductor is formed into a tapered shape to achieve impedance matching, then impedance matching is improved, but the electric field distribution broadens and differs from the waveguide distribution, causing electromagnetic wave leakage and increased conversion loss
Solution Approach 1:
The conversion structure extends in the vertical dimension by incorporating multiple layers (upper and lower conductor layers separated by a dielectric layer). This three-dimensional configuration allows the electric field distribution to transition more smoothly from the microstrip mode to the waveguide mode, reducing leakage while maintaining impedance matching through the tapered geometry in the horizontal dimension.
Solution Approach 2:
The conversion structure uses a composite configuration combining conductive layers and dielectric material. The dielectric layer between the upper and lower conductor layers provides field confinement and shapes the electric field distribution, helping to match the waveguide mode while reducing electromagnetic wave leakage compared to a single-layer tapered conductor.
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 achieves improved frequency characteristics and reduced conversion loss, enabling wider frequency bandwidth and enhanced stability against manufacturing defects, allowing for more compact and sophisticated high-frequency circuit designs.
Implementation Method 1
an array of sidewall-forming via-hole conductors that electrically connects the pair of sub-line part main conductor layers in the thickness direction
Implementation Method 2
a high-frequency transmission line connection structure, for electrically connecting a high-frequency transmission line conductor and a laminated waveguide to each other
Data Source
AI summary
The invention relates to a high-frequency transmission line connection structure, a circuit board having the connection structure, a high-frequency module having the circuit board, and a radar apparatus. A first laminated waveguide sub-line part (21) includes a pair of main conductor layers that oppose each other in a thickness direction with a dielectric layer (31) having the same thickness as a dielectric layer (31) of a microstrip line (1) interposed therebetween. A second laminated waveguide sub-line part (22) includes dielectric layers (31, 32) thicker than the dielectric layer of the first laminated waveguide sub-line part (21). A laminated waveguide main-line part (23) includes dielectric layers (31, 32, 33) thicker than the dielectric layers of the second laminated waveguide sub-line part (22). A conversion part (10) connected to the microstrip line (1) is formed by integrating with an upper main conductor layer constituting the respective line parts.