An Automated GA-HSMLFMM Co-Design Framework for Minimizing DDM in ILS Multipath Interference

To ensure the guidance accuracy and flight safety of instrument landing systems (ILSs), it is imperative to mitigate multipath interference caused by reflections from airport structures, whose core detrimental effect is the excess deviation of the difference in depth of modulation (DDM). This paper presents an automated design methodology with the explicit objective of directly minimizing DDM, employing a genetic algorithm (GA) to optimize additional metallic baffles adjacent to a building, thereby achieving a “stealth” effect for the building structure. The method encodes the layout parameters of additional metallic baffles adjacent to a building into chromosomes, searching for the optimal configuration through iterative evolution. Each generation applies the efficient half-space multilevel fast multipole method (HSMLFMM)—for the first time in ILS interference simulation—to accurately compute the radiation field of every candidate design. The maximum resultant DDM along the glide path serves as the fitness function for selection. Optimization and validation are conducted for four typical scenarios where the interference source is located 50, 100, 150, and 200 m from the runway centerline. The optimized DDM values are reduced to 4.49, 4.78, 4.63, and 4.87, respectively, all below the ICAO Annex 10 tolerance limit of 5μA for CAT III operations. The corresponding reduction percentages are 75.85%, 83.93%, 90.73%, and 90.19%, with a maximum reduction of 90.73% achieved in the 150 m scenario. This research establishes an efficient, automated closed-loop optimization workflow, which offers a viable approach for the intelligent and precision design of low-observable buildings at airports.