Five things about semi-rigid cable assemblies
2020.03.31
The most basic form of semi-rigid cable assembly is a coaxial transmission line composed of a metal pipe. Wherein, the metal pipe is generally a copper pipe forming an outer conductor, and a wire conductor is provided along a center line of the copper pipe. The center wire conductor is supported by a dielectric material, so as to be held on the same center axis of the outer conductor.
Examples of semi-rigid, moldable and semi-flexible cable assemblies
Here are the five most important things to know about semi-rigid cables:
1.Independent microwave components
It is extremely important to realize that the semi-rigid cable assembly itself is a key microwave component. This means that the specifications of semi-rigid cables are as important as the specifications of any coupler, bridge, or even amplifier. Properly made, cables can provide predictable stabilization in connecting other components in the system. As long as a good link is studied, it can be found that at a given frequency, electrical parameters including attenuation and voltage standing wave ratio play a vital role in the transmission and reception of radio frequency signals. Comparing semi-rigid cables with standard RG cables, it can be found that when semi-rigid cable assemblies are installed using brazed connectors, where space is appropriate and thermal cycling and other required tests must be carefully checked and performed, each It can take up to an hour or more; in contrast, connectors for flexible (non-semi-rigid) coaxial cables are crimp-type and can be installed in a minute or less.
2.Broadband application range
Semi-rigid cable assemblies typically support RF signal transmissions up to 65GHz. In addition, although not commonly used, cable assemblies terminated with 1.0mm connectors enable high-frequency applications up to 110GHz. Semi-rigid coaxial cables vary in size and range in diameter from 0.020 inches to 0.250 inches. In addition, 0.047-inch diameter cables using smaller connectors are becoming more and more popular because they can support higher frequencies. The 0.141-inch diameter semi-rigid coaxial cable is terminated with a high-frequency SMA or 2.92mm connector, and application conditions can typically be as high as 27GHz. Although 0.086 inch diameter semi-rigid coaxial cables are often used with SMA connectors, when they are terminated by 1.85mm connectors, the operating frequency can reach up to 65GHz.
3.Shaping and maintaining shape
For such cable assemblies, in order to fit into the designed system, they often need to be accurately shaped into various shapes. As the name suggests, a semi-rigid coaxial cable is a cable that is both rigid enough to maintain its shape and sufficiently flexible to be bent by hand. Shaping a semi-rigid cable into the desired shape is a risky job. In order to prevent damage to the outer pipe wall, special tools should be used to bend or shape the cable. In addition, once such a cable is shaped into a specific shape, it is extremely difficult to change its shape again. This is because the shape change often causes damage to the outer conductor, resulting in fine lines in the outer wall, and ultimately affecting the electrical performance of the cable assembly. Therefore, although such coaxial cables made of aluminum and soft copper are easy to shape and bend by hand, in order to minimize the risk of cable damage, special tools are still recommended for such operations.
Although plastic or semi-flexible coaxial cables are often grouped with semi-rigid coaxial cables, they are actually different types of coaxial cables. The plastic semi-rigid coaxial cable uses a spiral-wound conductive foil covered with a tin-filled outer braid, so its outer conductor is softer to a certain extent compared to a solid metal outer conductor. Although a plastic semi-rigid coaxial cable can be used as a substitute for a semi-rigid coaxial cable, its shape shaping is usually done by hand and can only maintain the approximate shape, which is not comparable to the shape retention of a standard semi-rigid coaxial cable. Since complex paths and assembly drawings are not required for general installations, this more flexible cable alternative has become extremely popular. This type of handmade plastic cable allows its length to be increased in small increments when purchased, and it allows it to be shaped into the desired shape when the product is assembled. In addition, this type of cable also has the advantages of semi-rigid coaxial cables with electrical properties close to the solid outer wall, lower production costs, and optional jacket materials.
4.Phase stability
Because semi-rigid coaxial cables are made of high-quality materials, they have extremely high electrical stability compared to flexible coaxial cables with wire braided outer conductors. The properties of metals and dielectric materials change with temperature, so the use of phase-stable cables is extremely important for many critical systems. In addition, in systems that require phase length control, phase-matched semi-rigid cables are often used. This is especially true for antenna systems with phased array antennas. This is because, in such an antenna system, the phase of the input signal plays an important role in electrically controlling the main beam of the antenna array. Modern mobile communication systems use this technology to optimize coverage under changing conditions to achieve the goal of reducing the number of antennas required for system performance optimization.
5. Low Passive Intermodulation (PIM)
Semi-rigid cable assemblies are usually made of non-ferrous metals, mainly copper. When a suitable connector is selected, this copper tube semi-rigid coaxial cable has excellent passive intermodulation performance, which makes it a modern multi-frequency wireless communication system including distributed antenna system (DAS) related equipment Ideal choice. With the increasing demand for complete coverage, the distributed antenna system market requires the use of more types of low-passive intermodulation products, including power splitters, combiners, amplifiers, and even high-end test equipment. Because the semi-rigid cable assembly can simultaneously meet the RF power and passive intermodulation requirements required by modern wireless communication systems, it becomes a natural fit for the above applications.
All in all, semi-rigid cable assemblies are vital microwave devices that are active in countless RF applications around the world today. Although semi-rigid technology is not new, semi-rigid components are still a popular choice for engineers due to its wideband characteristics, reliable electrical performance, and phase stability.
