A procedure for the design of shipboard antenna systems against the effects of electro magnetic pulse (EMP) is described. Exposure to EMP, especially that from a nuclear burst at high altitudes, can degrade the performance of unhard ened communication systems. The design procedure, or EMP algorithm (EMPAL), is a computer-aided iterative process which relies on a blend of ex perimental and computational techniques. Scale modeling and a transient electromag netic test facility (time domain range) are used to determine antenna system response functions. Lumped element models are used in combination with the circuit configuration and the EMP source as inputs to a circuit/systems simulation code (SPICE2) for response computations. The EMPAL procedure parallels the EMC (electromagnetic compatibility) design approach currently in use for Navy shipboard exterior rf communications systems design. OVERVIEW OF THE DESIGN PROBLEM EMP energy coupled into deliberate antennas poses a threat to EM equipment in the form of excessive voltage and possible excessive energy for a short period of time. Mitigation techniques involve the use of devices which automatically provide an alternate circuit path (usually to ground) whenever the voltage at a particular point exceeds a specified value. The alternate path must be capable of handling the current caused by the anticipated over-voltage. Circuit operation should return to normal operating conditions when the overvoltage condition ceases to exist. The device, of course, should not degrade the intended normal performance of the system it is designed to protect. Any procedure of mitigation design must meet the following requirements. First, if no protec tion device is required, none should be used. The reasons for this are economics and simplicity of design. Thus a shipboard antenna system must be analyzed to determine the need for protection. Since every ship topside configuration is unique, the design procedure must be sophisticated enough to characterize the antenna systems of individual NATIONAL LABORATORY CA 94550 ship classes. Once the need for a protection de vice has been established, any proposed mitigation design must be compatible with the ambient elec tromagnetic environment (EME) of the ship. It is not acceptable, if the ambient EME of the ship needlessly fires the protection device. The last design procedure requirement is a function of the ship design process. The speed with vrfiich the analysis can be executed also is very important. The procedure for shipboard exterior communication rf system design is an iterative process.[1] In the iterative process, the quality of the final design depends on the number of iterative cycles that can be executed in the given time frame.