| Low-observables engineers require accurate radar scattering computations from full-scale aircraft platforms due to their large size and complicated layering of materials (dielectric, resistive, impedance, etc) used for their construction. For helicopters in particular, complicated scattering mechanisms between the blades, hub, and body behave as corner reflectors and, if left untreated, lead to highly cross-polarized returns. A helicopter's signature is also time dependent due to the high rotational velocity of the spinning blades leading to Doppler frequency shifts. Thus, helicopters can be detected by Doppler-equipped radar more easily than fixed wing aircraft.; This thesis proposes a unique approach for computing helicopter scattering using a cohesive collection of novel, specialized tools. First, a generalized Method of Moments approach is introduced for simulating arbitrary layers of materials, including junctions where two or more materials meet. Corresponding generalized integral operators are then developed for a fast iterative solver (the Adaptive Integral Method) that reduces computational complexity and memory requirements. A highly efficient preconditioning technique, specialized for electromagnetic simulations, is also proposed to reduce the number of iterations required for convergence in the context of the proposed fast algorithm.; For sections of the structure possessing discrete circular symmetry, such as the helicopter rotor hub, a specialized method is proposed for computing radar scattering in conjunction with iterative solvers. The Fast Fourier Transform is then employed to accelerate the computation of the circulant impedance matrices associated with such discrete bodies of revolution (DBOR).; To compute the total scattered field from the entire heterogeneous structure, an iterative field refinement method is introduced to recover the interactions between the DBOR rotor hub, blade system, and helicopter body. The technique significantly reduces CPU time and memory requirements for geometries made up of many copies of an elemental structure (i.e. a helicopter blade system consisting of individual blades).; Lastly, a high-resolution signal processing approach is proposed for constructing the helicopter's RCS phenomenology in the time-frequency domain (i.e. under dynamic conditions). By accounting for additional current constraints, the method circumvents the uncertainty principle usually associated with this type of signal processing by generating the time-frequency distribution directly from the surface currents. |
