Recent advances in applied electromagnetism and microwave engineering

The thesis discusses the most recent advances in the following areas of (I) applied electromagnetism and (II) microwave engineering: (I.a) open scattering problems and (I.b) application programming interfaces; (II.a) microwave filters and diplexers, (II.b) transverse electromagnetic cells, (II.c) closed waveguide devices. For (I.a), an innovative method based on the equivalence principle and the spherical multipole expansion is developed. An arbitrarily shaped equivalence surface encloses a radiator solved numerically in a full-wave software. The equivalent currents on the equivalent surface are exported, and the impinging fields on a sphere enclosing the scatterer are computed using the free-space dyadic Green’s function. Eventually, the scattering problem is solved using the transmission matrix approach. For (I.b), novel user-friendly application programming interfaces for HFSS in MATLAB and Python are developed. For operation, they replace the numerical values of the variables that describe the HFSS model with placeholders. Since they do not resort to visual basic for applications scripts, the developed interfaces are easier to setup. For (II.a), attention is drawn to the design of filters and diplexers. Two technologies are considered: the combline cavity and the microstrip. For the former technology, inductive and capacitive end couplings are compared and both a filter and a diplexer are designed for L-band applications. For the latter technology, design compactness and low loss are pursued using complementary low- and band-pass spiral resonators, and two diplexers are developed for satellite communications and personal communications/5G applications. For (II.b), an open transverse electromagnetic cell is designed with a cube of side 10 cm as a uniform test volume and operating in the frequency range 30−1000 MHz. An asymmetric design with an off-centered septum between the outer conductors is pursued. In addition, the return loss is improved using a smooth taper that realizes a 50 Ω-characteristic impedance for minimum reflections. For (II.c), transformation optics is applied for analyzing closed waveguides. First, the boundary conditions are addressed, and the field is expanded to satisfy the boundary conditions. Second, cutoff eigenvalues and mode fields are computed for 2D cross sections. Third, mode fields are used to solve waveguide scattering problems with discrete discontinuities in a mode-matching framework. Fourth, transformation optics combined with hierarchical model reduction is applied to analyze waveguide devices with circular ports and smooth tapers.