RF Test Equipment Series: High Precision Coaxial Cable Assemblies
As there is an increasingly diverse range of wireless, RF, high-speed data, research, and sensing applications that involve the transmission, reception, and manipulation of RF signals, there is also a growing diversity of coaxial cable assemblies. One of the most significant uses of coaxial cable assemblies are in test and measurement and within high precision systems. These applications often require coaxial cable assemblies designed and manufactured with much higher performance criteria, as well as additional features beneficial to that specific application. The following is a brief highlight of those various performance criteria and features often sought often with high precision applications.
The main performance gaps between product-grade and precision coaxial cable assemblies is the mechanical tolerances of the connectors and cable, and several key electrical characteristics. These electrical parameters include insertion loss, VSWR, frequency range, and group delay. For instance, where a production-grade assembly may be manufactured with an acceptable max VSWR over 1.6:1, high precision test cables generally have VSWR below 1.4:1.
Moreover, for most precision applications, it is desirable to have as low of an insertion loss and as stable a group delay over the desired frequency range as possible. To meet these requirements, high-precision coaxial cables and connectors are often made with better tolerances, materials, a variety of cable layers that yield performance enhancements, and often undergo more rigorous quality control.
Rigid, Semi-flex, and Flexible Coaxial Cable Assemblies
RF Coaxial assemblies can come in rigid, semi-flex, or flexible coaxial cable types. The benefit of using rigid or semi-rigid coaxial cable is that in installations where there aren’t moving parts and the cables won’t undergo many connect/disconnect cycles, rigid and semi-flex coaxial cables can be made with better VSWR and lower insertion loss than comparable flexible coaxial cables. However, for test installations where several DUTs or handling may be required, flexible coaxial cables are most often used. Hence, within precision equipment, such as radar, sensing, research, and automated testing, rigid and semi-flex coaxial cables are common.
Skew Matched Coaxial Cable Pairs
For high-speed digital signal applications and other parallel communications, having the skew be as close as possible between the transmission lines carrying the paired signal is desirable. Hence, some manufacturers provide skew matched coaxial cable pairs that have precise and specified maximum skew parameters.
Phase Stable Coaxial Cables
For many testing applications that accommodate a variety of DUTs or require handling, benefit from phase stable coaxial cables. These cables are designed to hold their phase characteristics while undergoing flexing and bending. This enables a test setup to maintain calibration much better while undergoing movement than standard high precision coaxial cables. These types of cables are especially useful for manually calibrated test setups.
Low-PIM Coaxial Cables
In cases where PIM is a concern, Low-PIM coaxial cables can be used to ensure there is a minimum of additional PIM from the cable assembly. These assemblies are generally manufactured with extreme care and quality assurance, and often include a labeled specification for maximum PIM for each assembly. Typically, these types of coaxial cable assemblies are used with high power, or precision, wireless communications installations or PIM testing systems.
Hi-Rel & Armored Coaxial Cables
In some cases, high precision requirements also coincide with high reliability (Hi-Rel) requirements for rugged and extreme applications. Hence, there are Hi-Rel coaxial cable assemblies that are also built with Hi-Rel features, such as armored jacketing material and hermetically sealed connectors.
Useful High Precision Coaxial Cable Assemblies Links