MIL-HDBK-235: “Military Operational Electromagnetic Environmental Profiles”
MIL-HDBK-235 attempts to provide guidance for people trying to figure out the operational electromagnetic environment (EME) for a particular platform/program, as per MIL-STD-464 Section 5.3. (You can freely download MIL-HDBK-235 here.) If you read the appendices for that section of 464 (Always Read the Appendices!), you’ll find MIL-HDBK-235 called out several times for information and procedures on how to establish appropriate EME levels for a program. This will feel especially important, since the EME tables contained in the main text of 464 Section 5.3 contain some terrifying numbers–if you’re used to testing space hardware to 20 V/m, 464 Table III will tell you about multiple frequency ranges where both the peak and average field strength values are well above 150 V/m. So you follow the guidance of the appendix and turn to MIL-HDBK-235.
The problem is that MIL-HDBK-235 is a document with multiple parts, and every part except 235-1 (current rev: 1D, 2018) is classified. Below is the table listing the other document parts–the (U) next to each title just means that the title is unclassified, but the document as a whole is still inaccessible (which can feel a little soul-crushing when you just thought you’d found that answer to your problems, to be honest).
More than anything else, MIL-HDBK-235 is a guidance document for procurement agencies. The ones who need it will have access to the classified portions and can use them to set their EMEs appropriately. They can then spec the programs to the correct environments (although as 464 points out, those environments are often fluid–for instance if a unit that was designed to go in a terrestrial vehicle is redeployed on a naval vessel). Once the procuring agency sets those levels, the program can then do analyses to flow the requirements down to a MIL-STD-461 test level for different modules or equipment.
MIL-HDBK-235-1 has some helpful information about the general factors that go into the levels found in the classified portions of the document, as well as information about how to use that data. It also has guidance for doing average vs. peak power calculations, and deriving power density in the near and far fields for different types of antennas. What it does NOT do is tell you how to go from the External EMEs found either in its classified portions or the public tables of MIL-STD-464 Section 5.3 to MIL-STD-461 RS103 test levels. Simulations can be very helpful in doing that tailoring, taking into account the physical geometry of the platform, including the shielding effectiveness of different areas, and estimating how much field strength might be expected to develop in different regions when the whole platform is illuminated by plane waves with characteristics derived from MIL-HDBK-235 or similar documents.
TIP:
For those working in space applications, there is a NASA Johnson Space Center document, JSC-CR-06-070 “Space Vehicle RF Environments”, dating to 2018, that is publicly available.It has content very much like what is in classified sections of MIL-HDBK-235, but with no reference to sources. It includes some fascinating data surveying the EME of different orbits and at different times.