Coaxial Line Support Structure for Higher TE11 Cutoff
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Solution Overview
Problem
Conventional coaxial lines are limited in frequency range due to the TE11 mode cutoff frequency, restricting their use to frequencies below 90% of the cutoff frequency, and they face challenges in achieving increased bandwidth, especially in the millimeter wave range.
Innovation Solution
The coaxial line design incorporates supports with an inner insulating section and an outer conductive section, using materials like PTFE or ceramic for low dielectric losses, and conductive materials like copper or gold for electrical contact, which restricts the inner diameter and increases the cutoff frequency, allowing higher frequency transmission in TEM mode without transitioning to TE11 mode. Additionally, the use of absorber materials and specific geometries like radial patterns and coupling holes helps in attenuating unwanted modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the inner diameter of the outer conductor is increased to allow higher frequency transmission, then the bandwidth is improved, but the TE11 mode cutoff frequency decreases allowing unwanted mode propagation
Solution Approach 1:
The support structure is divided into two distinct functional sections: an inner insulating section that provides dielectric support and an outer conductive section that acts as an artificial inner conductor. This segmentation allows the outer conductive section to define an effective inner diameter that is smaller than the actual inner conductor diameter, thereby increasing the TE11 cutoff frequency while maintaining the physical space needed for high-frequency TEM mode transmission.
Solution Approach 2:
The outer conductive section of the support acts as an intermediary structure between the inner conductor and the outer conductor. It creates an artificial boundary that restricts the propagation of TE11 modes by establishing an effective inner diameter smaller than the actual inner conductor, thus preventing unwanted mode conversion while allowing the physical geometry to support high-frequency operation.
2Ease of manufacture
If conventional dielectric supports are used to maintain mechanical spacing, then manufacturing is simplified, but they cannot restrict the inner diameter to increase cutoff frequency
Solution Approach 1:
The support structure combines two different materials with complementary properties: an inner insulating section made of dielectric material (such as PTFE or ceramic) for mechanical support and low loss, and an outer conductive section made of conductive material (such as copper or gold) for electromagnetic mode restriction. This composite structure achieves both ease of manufacture through modular construction and precise control of the effective inner diameter through the conductive section's geometry.
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 enables the transmission of higher frequencies in TEM mode without converting to TE11 mode, enhancing bandwidth and supporting millimeter wave frequencies by increasing the cutoff frequency and effectively managing unwanted modes through improved electrical and mechanical contact.
Implementation Method 1
The cutoff frequency of a mode is the lowest frequency at which the mode may persist. For the TE11 mode this cutoff frequency is inverse proportional to the diameter of the conductors of the coaxial line.
Implementation Method 2
The inner insulating section is configured to be placed at an inner conductor of a coaxial line. Such a material may be a plastic material, preferably a material having low dielectric losses at high frequencies.
Implementation Method 3
The outer conductive section may include a conductive material, having low losses at high frequencies, which may include copper, gold, silver.
Implementation Method 4
Additionally, the use of absorber materials and specific geometries like radial patterns and coupling holes helps in attenuating unwanted modes.
Data Source
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AI summary
A coaxial line with a circular inner conductor and a coaxially arranged circular outer conductor, has multiple coaxial supports. Each support includes a body having an inner insulating section with an inner bore for the inner conductor and an outer conductive section radially around the inner insulating section. The outer conductive section is electrically connected to the outer conductor.