Key Design Controls for Consistent RF Performance in High-Frequency Coaxial Cable

Whether transmitting 30 MHz ultrasound echoes, supplying high-definition signals from a camera-based scope, or delivering power to a high-frequency RF ablation probe, coaxial cables must maintain consistent performance throughout their service life. Their design ensures the correct impedance, low attenuation, and stable phase response across the entire intended bandwidth. Even relatively small impedance discontinuities or increases in attenuation can affect signal integrity in sensitive high-frequency applications, depending on the system design and operating bandwidth..

Precision Dielectric Extrusion and Dimensional Tolerances

The electrical characteristics of a coaxial cable are determined by the relationship between the conductor diameter and dielectric insulation. Tolerances of up to 2% in either element can alter the characteristic impedance of a cable by up to two ohms and contribute to reflections and return loss. We use a precisely controlled extrusion facility that utilizes in-line real-time diameter feedback to control the concentricity and thickness of the PTFE and e-PTFE insulators to 2 percent tolerances. Our ICE and IVUS applications use e-PTFE, which has a low relative permittivity (εr ≈ 2.1) across frequencies from DC to 1 GHz.

Shield Construction and Transfer Impedance Minimization

Transfer impedance measures how effectively a coaxial cable prevents external RFI from entering the cable and internal signals from leaking out, and is typically expressed in ohms per meter (mΩ/m). For effective RFI and EMI shielding above 1 MHz, a shield with more than 95% coverage is typically required. This usually involves a double-shielded configuration, such as a foil layer combined with a tinned copper braid, for high-frequency surgical applications.

For RF ablation applications operating at 400–500 kHz, we use an additional semiconductive layer beneath the foil shield to reduce the risk of creepage.. The silver plating on the braid helps reduce surface resistance at the higher frequencies and provides a transfer impedance of under 5 mΩ/m.

Controlled Cable Assembly and Termination Techniques

Our team of highly skilled cable technicians at Hotten adheres to strict termination procedures to minimize the impact of the termination on overall cable performance. This includes precise control of conductor strip length and insulation clearances to within 0.008 inches, optimized solder temperature profiles to prevent dielectric degradation and properly controlled crimp compression on contacts which are confirmed through crimp quality is verified through pull testing against application-specific requirements. Our automated semi-rigid assembly machines precisely strip, align, solder and terminate cables. Automated inspection systems verify each connection to ensure that conductor position within the termination connector is perfectly centered and the dielectric surface is flush.

Environmental Stability—Temperature, Humidity, and Flex Effects

An otherwise perfectly manufactured coaxial cable assembly could still exhibit inconsistent performance in temperature-variable or humid clinical environments or after extensive flexing. We subject many designs to 96-hour thermal/humidity cycling (40°C, 95% RH), monitoring impedance and attenuation variations, and measure phase shift under flex conditions using robotic and camera-based test fixtures. Our materials are chosen to withstand significant temperature and humidity variations and offer a low coefficient of thermal expansion, such as FEP and ETFE jacketing which are hydrophobic and resist moisture absorption.

Conclusion

Delivering a high-performance, highly reliable coaxial cable is the result of the precise control of all four of these design factors. At Hotten’s modern manufacturing facility we have built extensive design, engineering and manufacturing capabilities across 10,000 square meters to develop and build over 300 unique cable specifications per year.

Whether a surgeon needs a perfectly controlled RF ablation signal or a diagnostic probe that provides the clearest image available, Hotten’s coaxial cable technology provides reliable and consistent performance across demanding applications.