Overview of Military Standards for RF Cables and Connectors
Many coaxial cable and connector types are available in the RF and microwave industry designed for specific purposes and applications; compatibility with other RF microwave components is achieved with universally accepted cable and connector standards. The US Department of Defense (DOD) develops standards for materials, facilities, engineering, and testing practices in order to improve military operational readiness and reduce costs and production time. DOD standards have adopted non-government standards and practices that meet DoD performance requirements. This process is managed by the Defense Standardization Program who provides the standards and relevant specifications. RF cables and connectors used in military applications have demanding requirements for environmental specifications, such as temperature, shock, and vibration; these requirements are specified in detail the US Department of Defense military standards in MIL-DTL-17J for coaxial cables and MIL-PRF-39012 RF for coaxial connectors.
Department of Defense Standards (DoD)
The Acquisition Streamlining and Standardization Information System (ASSIST) database is a list of defense and federal standardization documents as well as adopted non-government standards (NGS), and Materiel International Standardization Agreements (ISAs). The approved standardization documents in the database include:
> Defense specifications, standards, and handbooks
> Commercial item descriptions (CIDs) and federal specifications and standards
> NGS created by consensus procedures in non-government standards organizations
> Materiel ISAs within NATO countries which have been ratified by the US.
When developing defense standards and specifications, one must be authorized by a military defense agency or department as a Standardization Management Activities (SMA) organization. Military standardization documents in the DoD Index of Specifications and Standards can be found at the DoD Single Stock Point in Philadelphia while the Industry standards, for example, the Institute of Electrical and Electronics Engineers and American National Standards Institute, are available from the specific association that authored the standards and specifications. It is important to note that military specifications can change at any time and it’s a good practice to check to make sure that the latest revision is being referenced. These standards are often referred to by their acronyms such as, “MIL-STD” Military Standard, “MIL-SPEC” Military Specifications or “MilSpecs.” According to the Government Accountability Office (GAO), military specifications serve to “describe the physical and/or operational characteristics of a product” while military standards “detail the processes and materials to be used to make the product.”
Coaxial cables for military and aerospace applications must meet the standards and specifications in MIL-DTL-17 which details specifications for flexible and semi-rigid coaxial cables with solid and semisolid dielectric cores as well as single, dual, twin, and triaxial conductors intended for use in radio frequency applications. The most current version of MIL-DTL-17 is revision “J” produced in 2014. To locate a regulation for a specific part or its specifications, a Part or Identifying Number (PIN) is assigned which begins with the letter “M” for Military followed by the specification number, the corresponding slash sheet number, and the assigned dash number or “RG” number.
Coaxial connectors for military and aerospace applications must meet the standards and specifications in MIL-PRF-39012 which provides general requirements and test methods for RF connectors used with flexible and semirigid coaxial cables. This standard gives the following classification standards:
> Class 1 is a connector with “superior RF performance at specified frequencies” and
> Class 2 is a connector that provides a mechanical connection within an RF circuit.
This standard also describes categories by which connectors are classified:
- A = field serviceable
- B = non-field replaceable
- C = field replaceable solder center contact
- D = field replaceable crimp center contact
- E = field replaceable and
- F = field replaceable crimp, for semi-rigid cable
MIL-PRF-39012’s latest amendment “E” in 2014 (section 3.3.5) adds that recycled, recovered, or environmentally friendly materials “should be used to the maximum extent possible, provided that the material meets or exceeds the operational and maintenance requirements, and promotes economically advantageous life cycle costs.” MIL-PRF-39012 Rev. F specification sheet, produced in 2016, gives the PIN for connectors. For example, MIL-PRF-39012/55 is the PIN referring to an RF coaxial SMA connector plug with a pin contact where the letter “M” is followed by the basic specification sheet number, and a sequentially assigned four-digit dash number. The first digit in the dash number designates the material and plating of the connector body as in “0” for silver plated brass, “3” for passivated corrosion resistant steel, “4” for gold plated copper beryllium, or “7” for nickel plated brass. More specifically, M39012/55 – 3028 refers to an SMA connector pin made of passivated corrosion resistant steel.