Authored by: R. F. Eaton and C. J. Kmiec
ABSTRACT - As coaxial cables are used at ever higher frequencies in the Gigahertz range, cable losses become extremely important. Losses are functions of both Dk, dielectric constant, Df, tangent delta, of the polymer and the geometry of the cable construction. Control of the polymer architecture and additive package can reduce electrical losses in the cables fabricated from the polymer resulting in lower cable losses. Dk of a polymer is related a variety of chemical properties of the polymer: polarity, Tg, Tm etc. Df of a polymer is related to molecular motions of polar groups either along the polymer chain or the motion of polar molecules within the polymer matrix. We will discuss the Df contributions of the alpha, beta and gamma transition in polyethylene. Dk and Df are also functions of frequency and temperature.
INTRODUCTION
Introduction and Coaxial Cable: Background-Coaxial cables are is an important growing segment for the W&C industry. This report is a review and summary of the key parameters that control signal loss in COAX cable. We will show that chemistry fundamentals can be used to reduce losses in the resins to fabricate the coaxial cables. Intuitively one would expect electrical losses to be related to the dielectric tangent delta at the frequency of interest. If the polyethylene contained no polar groups, the various polymer molecular motions, the alpha, beta and gamma transitions in polyethylene and related polyolefins, would have little or no dielectric loss. Literature data shows the electrical tangent delta of a polyethylene is related to level of polar impurities in the case of polyethylene1.
Introduction and Coaxial Cable: Background-Coaxial cables are is an important growing segment for the W&C industry. This report is a review and summary of the key parameters that control signal loss in COAX cable. We will show that chemistry fundamentals can be used to reduce losses in the resins to fabricate the coaxial cables. Intuitively one would expect electrical losses to be related to the dielectric tangent delta at the frequency of interest. If the polyethylene contained no polar groups, the various polymer molecular motions, the alpha, beta and gamma transitions in polyethylene and related polyolefins, would have little or no dielectric loss. Literature data shows the electrical tangent delta of a polyethylene is related to level of polar impurities in the case of polyethylene1.
Coax Cables by Gas Injection Process: For over many years Coaxial cables have been used in the transmission of Community Antenna Television (CATV) and radio frequency cables. Both solid and foamed dielectrics are used for coax insulation. Foamed cable has lower electrical losses but is more susceptible to environmental degradation especially moisture pickup. The current foam process that is utilized requires a specialized process wherein typically nitrogen gas is injected via sonic technology into the polymer melt. Incorporation of the gas leads to creation of a foam with expansion levels reaching 70- 80%. Coaxial cable is used to transmit a signal (voice, video or data) received from head end/antenna to a final destination. Coaxial cables are used in a number of high frequency Applications.
Definition of Electrical Power Loss: In this study we will use simple equations to evaluate the influence of DC and DF on the decibels/100 ft of electrical loss of a commercial coaxial cable. The decibel or db is simply the 10 times log of the ratio of power input to the cable at one end to the power available at the other end of the coax: Db = 10 log10 [(Power output)/Power input)]
CONCLUSIONS
• We have shown that for a given coax diameter and skin effect losses, an increase in polymer tan delta will negatively impact coax loss especially in the gigahertz region where tan delta losses can overpower skin effect losses.
• Optimization of a polyethylene reactor train can significantly decrease the electrical loss of the polyethylene in the GHz frequency range.
• We have developed a direct relation between 2.47 GHz tan delta and a chemical product performance factor which can be used to optimize, minimize, dielectric losses in the product LDPE.
• We have shown that for a given coax diameter and skin effect losses, an increase in polymer tan delta will negatively impact coax loss especially in the gigahertz region where tan delta losses can overpower skin effect losses.
• Optimization of a polyethylene reactor train can significantly decrease the electrical loss of the polyethylene in the GHz frequency range.
• We have developed a direct relation between 2.47 GHz tan delta and a chemical product performance factor which can be used to optimize, minimize, dielectric losses in the product LDPE.
Garg Associates produce a wide variety of High Performance Wires and Cables ranging from ultra-miniature Fluoropolymer (PTFE, ETFE and FEP) equipment wire, thermo couple cable, high powered shielded Multicore cables to high speed data bus, low loss and Ethernet cables. Whether it is custom designed or a standard product, there is a solution to the most demanding environment and application.
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