Electromagnetic environmental effects modeling, simulation & test validation for cosite mitigation — an overview

Current and future electronic warfare (EW) & intelligence surveillance and reconnaissance (ISR) systems are becoming increasingly more electronically complex with requirements for external antennas and apertures that are susceptible to various sources of electromagnetic interference and compatibility (EMI/EMC). A reduction in EMI may be required in order to ensure interference free operation during active jamming and ISR, as these platforms evolve into more complex, multi-mission ISR networked systems. One of the most difficult EMI/EMC problems that result from integrating many transmitters, receivers and antennas on one platform is cosite EMI. Technologies such as advanced interference cancellation systems, cosite managers, advanced antenna design, and low-loss, multi-port antenna couplers are being investigated to mitigate cosite interference. One type of cosite interference is intermodulation. Intermodulation and intermodulation distortion (IMD) is the result of two or more signals of different frequencies being mixed together, forming additional signals at frequencies that are not, in general, at harmonic frequencies (integer multiples) of either. Sources for intermodulation include amplifiers, mixers, passive devices, antennas structural geometry and nearby objects and selection and corrosion of materials. For antenna systems, a simple approach to this problem is to physically separate the receive antenna from the transmit antenna, on platforms such as aircraft, helicopters, spacecraft, ships, and buildings. However this solution may not be possible due to limited space and other platform constraints. The IMD problem is usually too complex to be accomplished by a single numerical approach because the size of the structure is too large, the material properties and geometries are very complex, the number of parameters are considerable, and range of parameters are very computationally large. Another solution is to develop a cosite interference rejection approach to cancel the coupled power from the interfering coupled signal obtained by the receive antenna. This paper will review very basic to more complicated cosite interference phenomena and approaches to minimize these effects.