Coaxial to Coplanar Waveguide Launcher for Microwave Bolometry
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Solution Overview
Problem
Conventional coaxial thermistor bolometers face issues with inductive discontinuity and mechanical fragility due to the use of fine wires and metal barreters, leading to unsatisfactory reflection at higher frequencies and manufacturing challenges.
Innovation Solution
A dual-coplanar sensor architecture is developed, where radio frequency energy is launched from a coaxial airline to symmetrically arranged coplanar waveguides on a thin dielectric substrate, eliminating the need for fine wires by using planar thermistors of the same width as the center conductor, and incorporating tapered ground planes and capacitors to minimize reflections and enhance robustness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If bead thermistors are hung from fine wires in gaps of coaxial airline, then thermal isolation is achieved, but inductive discontinuity causes unsatisfactory reflection at higher frequencies
Solution Approach 1:
The patent extracts the thermistor from the traditional fine-wire suspension method and integrates it directly into the center conductor of the coaxial airline. This eliminates the complex three-dimensional structure and fine wire components while maintaining thermal isolation through direct integration, thereby reducing inductive discontinuity and improving reflection performance at higher frequencies.
Solution Approach 2:
The patent transitions from a three-dimensional fine-wire suspension structure to a planar integration approach where the thermistor is embedded within the center conductor. This dimensional simplification eliminates the sharp step discontinuities in the conductor path, reducing inductive effects and improving high-frequency performance while maintaining thermal isolation.
2Ease of manufacture
If fine wire is used to suspend bead thermistors, then thermal isolation is achieved, but the structure becomes difficult to assemble and easy to damage
Solution Approach 1:
The patent merges the thermistor mounting function with the center conductor structure itself. Instead of using separate fine wires for suspension, the thermistor is integrated directly into the center conductor, combining structural support and electrical connection functions. This eliminates fragile fine wires and simplifies assembly while improving mechanical robustness.
3Reliability
If metal barreters are used in thin-film terminations, then thermal isolation is achieved, but they are easily damaged with excess power
Solution Approach 1:
The patent employs a composite structure where the thermistor is integrated with the coaxial conductor system. This composite design allows the thermistor to handle excess power more effectively by distributing thermal and mechanical stresses across the integrated structure, rather than concentrating them in fragile thin-film metal barreters.
4Device complexity
If sharp step in conductor is used for thermistor mounting, then simple structure is achieved, but inductive discontinuity causes unsatisfactory reflection at higher frequencies
Solution Approach 1:
The patent incorporates preliminary impedance matching design in the transition section between coaxial and coplanar waveguide structures. By pre-designing the transition geometry to maintain characteristic impedance continuity, the patent prevents inductive discontinuities before they occur, eliminating reflection issues at higher frequencies while maintaining structural simplicity.
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 low reflections at higher frequencies, improves manufacturing robustness, and allows for high-frequency sensors up to 50 GHz with extended frequency range potential, making it suitable for national primary standards and calibration laboratories.
Implementation Method 1
A dual-coplanar sensor architecture is constructed by launching radio frequency energy from a coaxial airline to a unique arrangement of coplanar waveguides
Implementation Method 2
Capacitors are arranged between the end of the termination resistors that are not connected to the input, and the ground planes, to complete a path for high-frequency current
Implementation Method 3
The coplanar waveguides are tapered, while maintaining the required impedance to a width such that the center conductor is approximately the same width as a temperature-dependent resistive termination element used to terminate the coplanar waveguide
Data Source
AI summary
A dual-coplanar sensor architecture is constructed by launching from coaxial airline to a unique arrangement of coplanar waveguides, arranged symmetrically on both sides of a thin dielectric substrate. The center conductor of the coaxial airline makes electrical contact with the middle conductor of both the top and bottom coplanar waveguides. The characteristic impedance of the top and bottom coplanar waveguides is designed to be approximately twice the characteristic impedance of the coaxial airline, such that the parallel combination of the two coplanar waveguides is the characteristic impedance of the coaxial airline. Further, steps in both the ground planes and center conductor at the point of transition from coaxial to coplanar are used to tune the launch and minimize reflection at the launch.