FOAMED POLYETHYLENE COAXIAL CABLES

Abstract : Coaxial cables using foamed or cellular polyethylene were constructed. One of these cables having the same overall diameter and characteristic impedance as the standard solid dielectric RG-11/U type was investigated in detail. The results of tests conducted in the humidity chamber showed that water vapor is capable of penetrating the jacket of the cable, entering the individual cells of the dielectric and increasing the losses of this cable. It was further demonstrated that the means by which the ends of the cable are sealed can affect the magnitude of the attenuation increase by a factor of two to one. Although water vapor can enter the cellular dielectric, the increase in attenuation which results is only approximately 11 percent of the original value at 250 mc whereas at this same frequency the cellular dielectric cable has 32 percent less attenuation than the solid dielectric RG-11/U cable. This still represents a 25 percent advantage of the cellular dielectric cable over the solid dielectric cable in the same physical size. Based upon these results, the use of cellular polyethylene dielectrics in coaxial cables appears to offer decided advantages by providing lower losses and lower capacitance without sacrificing physical size and weight.