Coaxial Tube Guided Wave Radar Level Gauge for Low Dielectric and Interface Measurement

Some liquids barely reflect a radar signal: light hydrocarbons, liquefied gases and solvents have low dielectric constants that defeat ordinary level instruments. The coaxial tube guided wave radar concentrates the signal inside a pipe waveguide, delivering the highest accuracy in guided wave radar and the ability to measure foam, steam and liquid-liquid interfaces.

Why Do You Need a Coaxial Tube Guided Wave Radar?

Low dielectric constant media are the hardest level measurement challenge in industry. Liquids such as light oils, liquefied gases and many solvents reflect microwave energy so weakly that non-contact radar receives almost no echo, and ultrasonic instruments fail entirely on vapor and foam. Standard guided wave probes improve the signal but still struggle with very low dielectric media. A coaxial tube design solves this fundamentally: the radar signal travels inside a coaxial pipe that confines and guides the microwave energy, dramatically strengthening the reflection from the liquid surface. This makes measurement possible and accurate where other technologies cannot measure at all. The coaxial construction also isolates the signal from external interference, handles slight foam and steam, and enables interface measurement between two immiscible liquids, making it the professional choice for hydrocarbon storage, chemical processing and other demanding applications.

Working Principle: Guided Wave Radar with Coaxial Pipe Waveguide

The gauge transmits microwave pulses down a coaxial probe, where an inner conductor and outer tube form a waveguide that confines the signal along the probe's full length. When the pulse reaches the product surface, the change in dielectric constant causes a reflection that travels back to the electronics; the round-trip time is converted into an accurate level value. Because the energy is confined within the coaxial structure rather than radiating outward, the reflection is far stronger than with open probes, giving the highest measurement accuracy available in guided wave radar. The confined signal also provides extremely strong anti-interference performance, immune to vessel walls, agitators and nearby structures. In addition to level, the design can detect the interface between two immiscible liquids, such as water and oil, and it operates reliably in applications with slight foam and steam that scatter free-space signals.

Structural Advantages of the Coaxial Tube Gauge

• Coaxial pipe waveguide: confines signal for strongest reflection.
• Highest guided wave accuracy: superior precision in its class.
• Low dielectric measurement: measures light oils, liquefied gases, solvents.
• Interface measurement: detects liquid-liquid boundaries.
• Extreme anti-interference: immune to walls, agitators, structures.
• Foam and steam tolerant: reliable in difficult atmospheres.
• Concentrated signal energy: no signal loss in the vessel.
• Special process capability: suitable for demanding chemical service.

Pain Point Analysis: 2 Challenging Working Conditions

Application Cases

Product Advantages

• Coaxial pipe waveguide for strongest signal reflection
• Highest accuracy among guided wave radars
• Measures low dielectric constant media reliably
• Liquid-liquid interface measurement capability
• Extremely strong anti-interference performance
• Operates with slight foam and steam
• Concentrated signal, no vessel signal loss
• Suitable for special chemical processes

Technical Parameters

SEO FAQ

Q1: Why is a coaxial tube better than an open guided wave probe?

An open probe radiates the microwave signal into the surrounding medium, so part of the energy spreads outward and the reflection from the surface is relatively weak. A coaxial tube probe confines the signal inside a pipe formed by an inner conductor and an outer tube, guiding all the energy along the probe with minimal loss. The result is a much stronger reflection from the product surface, which is exactly what low dielectric constant liquids need, since they reflect microwave energy weakly. The confined signal also cannot be disturbed by vessel walls, agitators or nearby structures, giving the coaxial design the highest accuracy and strongest anti-interference performance in the guided wave radar family.

Q2: What is a low dielectric constant and why does it matter?

Dielectric constant is a measure of how strongly a material reflects microwave energy; water has a high value around 80, while light hydrocarbons such as gasoline, naphtha and liquefied gases have values of only 1.5 to 3. The lower the dielectric constant, the weaker the reflection a radar signal receives from the surface. For very low values, non-contact radar and open guided wave probes receive almost no usable echo, making level measurement unreliable or impossible. The coaxial tube design overcomes this by concentrating the signal and amplifying the reflection, enabling accurate measurement of low dielectric media that other radars cannot handle. If your medium is a light oil, solvent or liquefied gas, a coaxial guided wave gauge is often the only reliable choice.

Q3: Can the gauge measure interface between two liquids?

Yes. Because the guided wave signal travels through the upper liquid and reflects at the boundary where the dielectric constant changes, the gauge can detect the interface between two immiscible liquids, such as an oil layer floating on water. This is valuable in separators, decanters and storage tanks where operators need to know not just the total level but the position of the interface, for example to draw off the correct product or prevent water carryover. The coaxial design's strong signal makes interface detection particularly reliable. When ordering, specify that interface measurement is required so the gauge is configured with the appropriate processing.

Q4: How does the gauge perform with foam and steam?

Foam and steam scatter free-space radar and ultrasonic signals, causing lost echoes and false readings. The coaxial guided wave design is largely immune to both: the signal travels inside the pipe waveguide, so foam on the surface and steam in the vessel atmosphere do not disperse the signal energy. Slight foam layers can be penetrated or their effect minimized, and steam has no meaningful impact on the guided measurement. This makes the gauge suitable for chemical reactors, separators and storage tanks where foaming occurs during filling or processing, and where steam is present above hot liquids. For heavy or conductive foam, consult our engineers for configuration guidance.

Q5: What support and customization do you offer?

As the manufacturer, we provide direct engineering support including probe selection, dielectric evaluation, interface measurement configuration and installation guidance. Customization options include probe length, process connection, output protocol, materials for corrosive service, labeling and packaging, plus OEM and ODM programs. Every gauge is factory-calibrated and tested before shipment, and our engineers can review your medium's properties and vessel configuration to confirm the correct coaxial design. Contact us with your liquid properties, vessel dimensions and measurement requirements for a tailored recommendation.

Why Choose Our Coaxial Tube Guided Wave Radar Level Gauge?

Some measurements are impossible until the right technology arrives. The coaxial tube guided wave radar makes the impossible routine: it measures low dielectric liquids that defeat open probes, detects oil-water interfaces that confuse ordinary gauges, and delivers the highest accuracy in guided wave radar with immunity to foam, steam and structural interference. As the manufacturer, you receive factory calibration, application-matched probe configuration and direct engineering support. When your medium barely reflects and your measurement must be exact, choose the coaxial gauge that captures the signal others lose.