Here is a list of 25 Electromagnetic Countermeasures categories. It encompasses a wide range including emi/rfi filters, emc countermeasure components, air ionizers, anechoic chambers, etc. You can search for an overview, principle, and usage of each category, as well as find manufacturers and distributors.
*This ranking is solely among the companies registered with Metoree, sorted by the number of employees. Please use this as a rough guide to understand their scale.