The power handling capability of a cable assembly is related to the ability of the assembly to dissipate heat generated by resistive and dielectric losses. Thermal expansion and/or breakdown can be the result of exceeding the maximum allowable temperature of the materials used in the cable assembly, especially dielectric. It should be noted that 70% or more of the copper loss, which is normally the largest component of insertion loss, is dissipated in the center conductor. In general, the power handling capability of a given cable is inversely proportional to its attenuation, and is directly related to its size. Other factors are the heat transfer properties of the cable components, particularly the dielectric.
Cable power ratings must be de-rated by correction factor for the ambient temperature, altitude, and VSWR encountered in a particular situation. High ambient temperature and altitude reduce the power rating of a cable by impeding heat transfer. Reflection loss or VSWR reduces power rating by causing localized hot spots in the cable. To select a cable that will meet the power requirements, determine the average input power at the highest required frequency; then determine the effective input power from the following equation:
Effective Power = Avg. Power x VSWR correction (K) x Temp. corr. x Alt. corr. (Figures 5, 6, and 7)
The primary factor restricting connector power handling is over heating of the connector center conductor, and thus the connector center conductor should always be equal or larger than the cable center conductor.
Figure 5 - VSWR Correction Multiplier K
Figure 6 - Power Temperature Correction Factor
Figure 7 Power Altitude Correction Factor