MIL-STD-285: Military Testing of Attenuation Measurements For Enclosures

The MIL-STD-285 standard measures the shielding effectiveness in respect to the frequency range from 100 kHz to 10 GHz. All samples that qualify for this testing must be a) some kind of enclosure; b) must be applied as a shield. Enclosure examples may vary greatly since there is a vast range of enclosures available. This includes glass windows, conduits, and nanomaterials such as carbon nanotubes.

As long as the enclosure houses some kind of material in some capacity, such as a conduit with wire sent through, then the sample would qualify. See the figure below shows an example with conduit.

On the transmitting side, the conduit is connected to the test chamber bulkhead and has a signal being transmitted through it. On the receiving end, the opening of the conduit where the signal is measured to see the signal loss (attenuation) for the overall shielding effectiveness of the sample.

The test setup is the same as other shielding effectiveness, first determining the dynamic range of the unit/sample and the actual measurement of the signal for the sample in question.

Scope of Military Shielding Effectiveness Standard Testing

The requirements of the test setup for MIL-STD-285 testing are relatively straight forward. The arrangement of signal sources measuring equipment, pick-up devices, and shielded enclosures are all detailed within the standard. All power lines, RF cables, and other utilities entering the shielded enclosure must be in place when tests are conducted. Special care should be taken to make measurements in the vicinity of utility entrances, doors, and access panels.

An electromagnetic barrier is a topologically closed surface created to prevent or limit fields and conducted transients from entering the enclosed space. The electromagnetic barrier consists of the shield and POE treatments. This barrier encloses the protected volume and special protective volumes if required.

An electromagnetic closure is a treatment to prevent excessive electromagnetic field leakage at an aperture point of entry. Examples of closure techniques at a seam between two metal plates include welding, brazing, or soldering and metal-to-metal contact under pressure applied with a mechanical fastening.

Mission-critical equipment is defined as all equipment required to directly support a critical mission, success, or failure of which could affect the outcome of the battle. Mission-critical equipment often refers to all communications-electronics and support equipment that must be protected in order to perform critical trans- and post-HEMP attack missions.

point-of-entry (POE) is a location on the electromagnetic barrier where the shield is penetrated and energy may enter the protected volume. This will occur unless an adequate POE protective device is provided. POEs are classified as aperture POEs or penetrating conductors according to the type of penetration. They are also classified as architectural, mechanical, structural, or electrical POEs according to the engineering discipline in which they are usually encountered.

Expert MIL-STD 285 Regulatory Compliance

Keystone Compliance has the capabilities to test any size of enclosure to MIL-STD-285. We have tested large items such as entire on-site installation buildings and small items that can be easily transported to our lab.

In addition to MIL-STD-285 compliance testing, Keystone has a full scope of expertise including environmental and package testing such as cold chain, accelerated aging, and temperature. Our team strives to give our customers more time and energy on product development instead of testing. Lastly, Keystone has a full lab of test equipment which permits us to provide short lead times on scheduling.

Are you ready to partner with Keystone Compliance to determine the shielding effectiveness of your product when tested to the requirements of MIL-STD 285? Let’s get started!