− Time domain magnetic field integral equation (MFIE) is discretized using divergenceconforming Rao-Wilton-Glisson (RWG) and curl-conforming Buffa-Christiansen (BC) functions as spatial basis and testing functions, respectively. The resulting mixed discretization scheme, unlike the classical scheme which uses RWG functions as both basis and testing functions, is "proper": Testing functions belong to dual space of the basis functions. Numerical results demonstrate that the marching on-in-time (MOT) solution of the mixed discretized MFIE yields more accurate results than that of classically discretized MFIE.
INTRODUCTIONMagnetic field integral equation (MFIE) is a second kind integral equation, i.e., it is constructed as a summation of an identity and a linear operator. Because of the identity operator, the domain and range of the MFIE operator are identical and a consistent discretization scheme should use basis and testing functions, which belong to dual spaces of each other [1]. In particular, the testing function should be in the dual space of the MFIE operator's range (and domain) to obtain a "proper" discretization scheme. Classical marching on-intime (MOT) based MFIE solvers expand the unknown surface current density using divergence-conforming Rao-Wilton-Glisson (RWG) functions [2] in space and polynomial functions in time. To obtain a proper discretization, spatial testing should be done using curl-conforming n × RWG functions, which belong to dual space of the divergence conforming RWG basis functions. However, resulting MOT matrix becomes singular and cannot be inverted accurately at every time step as required by the MOT scheme. Therefore, classical implementations use RWG functions (but not their duals) for spatial testing and violates the requirement of the proper discretization described above. Even though the solution of the MOT matrix system resulting from this discretization scheme converges fast, it yields inaccurate results.In this work, time domain MFIE is discretized using the mixed discretization scheme, which is originally proposed for discretizing the frequency domain MFIE [3]. Mixed discretization scheme makes use of recently proposed Buffa-Christiansen (BC) functions [4]-[5] to produce well-conditioned MOT matrices without violating the requirement of the proper discretization described above. Current density is expanded using divergence-conforming RWG functions in space and spatial testing is carried out using curl-conforming n × BC functions, which belong to dual space of the divergence-conforming RWG functions.