Hermetic and the concept of hermiticity in RF components and devices is derived from the Greek for impenetrable barrier, and air/water tightness. This is a critical feature of many military/defense, industrial, and aerospace systems that are exposed to harsh environments where air pressure changes, moisture ingress, or introduction of debris could degrade or catastrophically damage a system. Hermetically Sealed RF, Microwave and Millimeter Wave Connectors and Adapters are a method of ensuring hermeticity of hermetically connectorized RF components and devices.
In many cases hermetically sealed RF connectors and adapters are needed to ensure that the inert gas contained within an RF system is sealed as well as to keep out external contaminants from the environment. This could be that a given module needs to be pressurized to a certain atmosphere, or that the module is purged with inert gasses to prevent corrosion or gas exchange with certain electronic components that may be prone to damage from chemical reactions due to “poisoning” from normal atmospheric gasses.
Hermetically sealed RF connectors and adapters typically use a barrier technology within the coaxial connector that provides a hermetic seal on both sides of the barrier. This hermetic seal is often glass that is soldered into the connector body using a specialized technique to ensure that there are no gaps or channels in the seal. Given that many of the applications that make use of hermetically sealed connectors/adapters require these adapters to meet certain stringent grades of hermeticity, even commercial-off-the-shelf (COTS) variations of these connectors are made to military/defense, aerospace, or space standards. A common military standard (MIL-SPEC) for hermetically sealed coaxial connectors/adapters is MIL-STD-348B.
These types of adapters are often used at the interfaces to coaxial connectorized packages and enclosures. Hence, there are many variations of hermetically sealed coaxial connectors/adapters in bulkhead form, as well as 4-hole flange form. Even with the bulkhead or 4-hole flange form, these adapters and connectors can still be used for inline adaptation in non-hermetic applications. This could be viable as these connectors are often also designed to be extremely rugged and have a much wider operational temperature range than typical coaxial connectors and adapters. Hence, these connectors are often used when ruggedness, resilience, long lifetime, and extreme thermal conditions are key considerations even if hermeticity isn’t required.