Abstract: PTFE (DuPont Teflon) has been used as a dielectric material for transmission cables for decades. At room temperature, PTFE undergoes a state change, causing a step change in its volume, as well as a change in relative dielectric constant, and exhibits a "lag" effect of electrical length variation. These changes in electrical length are difficult to reliably predict and measure through system software or other means, resulting in a reduction in system performance. The development of organic and inorganic dielectric materials has brought about tremendous improvements in some basic performance indicators. This article will compare several coaxial cable technologies: • Phase change relationship due to temperature changes • Relationship between tracking performance and temperature variation between multiple sets of cables • Electrical length tracking performance between multiple sets of cables when ambient temperature changes • Repeated electrical length after multiple temperature cycles performance In addition, the parasitic phase noise generated by the vibration and interaction between the conductor structure and the medium, and the associated electrical length parameters, are discussed below. Oliver Heaviside notes that wrapping a telephone line with an insulator will improve signal quality and effective communication distance. In 1880 he applied for the patent for the world's first coaxial cable. In 1929, an engineer at Bell Telephone Laboratories of the American Telephone and Telegraph Company applied for the patent for the first modern coaxial cable. According to today's standards, it consists of two coaxial metal tubes that are isolated by air and appear rough. In the 1930s, Eucommia rubber (a natural rubber) was the main medium of choice for early flexible coaxial cables. During the Second World War, polyethylene became the main insulating dielectric material. The "foaming" process was developed in the 1950s to reduce cable capacitance and losses. Solid full-density polytetrafluoroethylene (PTFE) or Teflon was widely used in the 1960s. Its higher temperature range, lower loss factor, lower dielectric constant and consistent performance over a wider temperature and frequency range make it an ideal coaxial cable medium. In the 1970s and 1980s, manufacturers began to use the stretch-expanded low-density version of PTFE to further achieve better performance. The increased demand for electrical length stability in the 1990s enabled manufacturers to begin using ultra low density PTFE media. These products do have significant improvements, but there are still some inherent limitations. The most important limitation is the phase-to-temperature "turning point" problem: the electrical length step change due to the basic material properties of the PTFE molecule. This effect can be minimized, but it cannot be eliminated. In 2004, coaxial cable products used TF4 technology to solve this problem. Further optimization and improvement of the process in 2015, the development of the new TF4 technology, compared to PTFE dielectric materials, it has a very obvious advantage in phase-sensitive applications. An ideal microwave cable assembly should have zero loss, zero energy reflection, and zero electrical length variation. These ideal attributes should remain unchanged under any environmental conditions in which the system components are located. In practical applications, we must strive to achieve these ideal attributes. In reality, however, the change in the electrical length of the coaxial cable assembly is indeed related to the change in ambient temperature. A. Relationship between phase change and temperature change It is well known that the metal used to form the coaxial cable assembly has a positive expansion temperature coefficient. The electrical length is directly related to the physical length. Obviously, as the temperature rises, the physical length increases and the electrical length increases. In contrast, the electrical length of most microwave cable assemblies has a negative temperature coefficient. Figure 1 illustrates the effect of temperature on the electrical length of an ideal cable assembly. figure 1 The axial length of the center conductor increases as the temperature increases. The outer conductor also grows with temperature and directly affects the change in diameter of the outer conductor. This causes a slight change in the density of the medium to change the relative dielectric constant. This interaction has an effect on the dielectric constant such that the change in electrical length is inversely proportional to the expansion-contraction effect of the metal. This phenomenon is crucial, making it possible to theoretically balance both to achieve zero temperature phase changes. In fact, in cable assemblies using PTFE as the propagation medium, there is always a step change in the dielectric constant at room temperature, resulting in a corresponding change in electrical length. Figure 2 illustrates the coaxial cable of PTFE media, the effect of temperature on phase. figure 2 B, phase tracking and temperature relationship In fact, phase-matched cable assemblies do not remain relatively matched as temperature changes. Phase tracking refers to the ability to maintain the initial phase value between cable assemblies. Figure 3 illustrates two cable assemblies that have been phase-matched at room temperature, with phase tracking changing as temperature changes. image 3 Many factors determine good phase tracking performance. The most critical is the consistency of the cable in all aspects of the unit length. Including the capacitance, impedance, and consistency of the mechanical properties of the conductor, these are critical to the quality of the phase tracking performance. The phase matching value at any temperature is obtained by adding the initial matching value to the phase tracking change value. Figure 4 illustrates that phase tracking is also related to the initial phase difference when the cable is matched at room temperature. Figure 4 C, phase matching at room temperature
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