The most common types of coaxial cable assemblies most engineers encounter are made with flexible coaxial cables. These cables use a braided or stranded type of outer conductor and a highly flexible dielectric and outer jacket material. An outer jacket is necessary for flexible coaxial cables to prevent environmental ingress. Flexible coaxial cable assemblies are common, as many applications require ease of installation and routing and are willing to sacrifice some performance to allow for that. However, when performance is necessary and routing is somewhat known in advance, semi rigid cable assemblies may be a much better fit.
Unlike flexible coaxial cables, semi rigid coaxial cable use a rigid, often solid metallic, outer conductor that requires the cable to be formed into the desired shape to ensure proper fit and installation. Once formed, these cables hold their shape. As a result of this rigidity, semi rigid RF cables are typically phase stable and much more reliable than flexible coaxial connectors. However, forming semi rigid cables often requires specialized forming tools to allow the cable to be bent or formed without damaging the outer tubing wall. More often than not, semi rigid coaxial cables can only be reliably formed/bent once, repeated attempts to form/bend this type of coaxial cable often results in damage to the outer tubing.
Generally, semi rigid cable assemblies are made of high-quality materials and are designed to be extremely rugged and reliable. As part of this, semi rigid coaxial cable assemblies are often phase stable over temperature and sometimes even pressure. Hence, these types of cables are commonly used in phased array antenna systems in phase matched pairs/groups in applications that require controlled phase lengths.
Given the formable nature of semi rigid coaxial cables, these coax cables are generally made with non-ferrous materials, mostly of copper and plated copper materials. As a result of quality construction and material choices, semi rigid coaxial cables are typically low passive intermodulation (PIM) interconnects. Like other coaxial cables, these semi rigid cable assemblies can allow for pairings of a variety of cable types with coaxial connector types, including angled coaxial connector types that reduce the need to form bends in the semi rigid RF cable.
Key Electrical Specifications, Performance Parameters, & Features for Semi Rigid Coaxial Cable Assemblies
- Frequency range [Hz]
- VSWR [ratio]
- Insertion loss [dB]
- Impedance [Ohms]
- Velocity of propagation [%c]
- Power handling (CW, peak) [Watts]
- Mount Method [flange]
- Coaxial connector type [N, SMA, 3.5 mm etc.]
- Contact material/plating [beryllium copper, gold over nickel, silver etc.]
- Dielectric type/material [PTFE, PCTFE, microporous PTFE etc.]
- Coupling nut material/plating [passivated stainless steel etc.]