Coaxial Feed-Through Impedance Matching for Radar Level Gauging
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Solution Overview
Problem
Conventional feed-throughs for guided wave radar systems in storage tanks experience significant microwave power losses due to impedance mismatches between the feed-through and the tank nozzle or top surface, leading to inaccurate level measurements and limited detection range.
Innovation Solution
The implementation of coaxial feed-throughs with a dielectric sleeve, divided into upper and lower segments, where the lower segment has an impedance at least 40% higher than the upper segment, minimizing impedance mismatch and reducing microwave power losses by acting as a coaxial transmission line, thereby enhancing signal propagation and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a conventional 50 ohm coaxial feed-through is used, then the feed-through structure is simple and easy to manufacture, but significant impedance mismatch occurs between the feed-through and the tank nozzle or top surface, leading to microwave power losses
Solution Approach 1:
The dielectric sleeve is divided into an upper segment and a lower segment with different dielectric constants. The upper segment has a first dielectric constant while the lower segment has a second dielectric constant that is at least 40% higher, creating impedance transformation zones that reduce microwave power losses at the transition interfaces.
Solution Approach 2:
Different segments of the dielectric sleeve are assigned different dielectric properties tailored to their specific functions. The upper segment provides impedance matching to the 50 ohm coaxial cable, while the lower segment provides impedance transformation to match the tank nozzle or top surface, optimizing performance at each location.
2Measurement precision
If the dielectric sleeve is divided into segments with different dielectric constants, then impedance matching is improved and microwave power losses are reduced, but the manufacturing complexity increases
Solution Approach 1:
The dielectric sleeve is segmented into distinct sections with different dielectric constants, allowing each segment to be optimized for its specific impedance transformation function while maintaining modular assembly that balances manufacturing complexity with measurement precision.
Solution Approach 2:
The dielectric constant parameter is varied along the length of the sleeve, with the lower segment having a dielectric constant at least 40% higher than the upper segment. This parameter change enables improved impedance matching and measurement accuracy while using standard dielectric materials and manufacturing processes.
3Length of stationary object
If the lower dielectric segment has an impedance at least 40% higher than the upper segment, then impedance mismatch is minimized and detection range is extended, but the device complexity increases
Solution Approach 1:
The impedance of the lower dielectric segment is designed to be at least 40% higher than the upper segment, creating an impedance transformation profile that extends detection range by reducing reflections and improving signal propagation, while maintaining a relatively simple two-segment structure.
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 significantly reduces microwave power losses by 5 dB or more, improving the accuracy of level measurements and extending the detection range, while maintaining mechanical and process sealing integrity.
Implementation Method 1
The dielectric sleeve of this CTL generally has a total electrical length of about 0.8λ to 1.2λ along the probe direction, where λ is the center wavelength associated to the bandwidth of the interrogation signal
Implementation Method 2
the lower CTL segment has a different impedance than the upper CTL segment, such that the output impedance of the lower CTL segment minimizes the impedance mismatch between the feed-through and the nozzle
Implementation Method 3
The dielectric sleeve can be divided into two regions: an upper dielectric sleeve and a lower dielectric sleeve. The lower dielectric sleeve can have a different dielectric constant than the upper dielectric sleeve
Data Source
Figure 1A
Figure 1B
Figure 2
AI summary
A coaxial feed-through device (feed-through 100) for coupling a received process connection (2) to a storage tank (tank 40) including an inner electrical conductor (probe) (10), an outer electrical conductor (20); and a dielectric sleeve disposed between the probe and the outer electrical conductor. The dielectric sleeve is configured to provide an upper coaxial transmission line segment (upper CTL segment) (100a) providing a substantially 50 ohm impedance and a lower coaxial transmission line segment (lower CTL segment) (110b) which includes one or more sub-segments (100 b1 or 100b2, 100b' or 100b'') having an impedance that is at least forty (40%) percent higher as compared to the substantially 50 ohm impedance.