Current and future intelligence, surveillance and reconnaissance (ISR) systems are becoming increasingly more electronically complex with requirements for apertures that are susceptible to various sources of electromagnetic interference and compatibility (EMI/EMC). Validated electromagnetic environmental effects modeling and simulation of these advanced apertures is critical to enhance overall ISR performance. The current tactical battlespace presents a complex operating electromagnetic environment. Electromagnetic modeling and simulation toolsets are faced with challenges including RF design of realistic but complex problems which must be solved using less computation time. Aperture-related design, modeling and simulation focuses on antenna gain characteristics, developing phased array antenna concepts as well as analyzing and minimizing the electromagnetic interactions among elements of an electronic system and its environment. As apertures become more closely spaced together on a specific platform architecture, interference may occur as a result of both near and far field coupling as well as cosite intermodulation. This interference can involve amplifier distortion, limits on input/output power, interferences due to interaction between desired and unwanted signals, changes in input impedance, radiation impedance, current distribution and radiation patterns. Northrop Grumman, in collaboration with the Polytechnic Institute of New York University, are developing advanced electromagnetic modeling and simulation toolsets including first principle electromagnetic codes, such as method of moments (MoM) and Multilevel Fast Multipole Method (MLFMM), to perform full wave analysis of near field coupling and obtain the effective radiation patterns for each of the localized aperture systems. A reduction in EMI may be required in order to ensure enough interference free operation during active ISR, as these platforms evolve into more complex, multi-mission ISR networked systems. New platforms are going to have unique electromagnetic compatibility issues that require both phenomenology and validated first principal electromagnetic modeling so that the platform can provide a broad array of wideband passive sensors as well as active arrays. This paper will review very basic to more complicated interference phenomena and approaches to minimize these effects.