Radio frequency (RF) refers to the field of study that examines electromagnetic waves with frequencies between 3kHz (λ=100km) and 300GHz (λ=1mm), encompassing both microwaves and millimeter waves. Investigations at RF begins with solving Maxwell's equations and finding their solutions for appropriate boundary conditions. At RF frequencies, the phase variation of the signal is significant enough to break down the lumped element approximations of low-frequency circuit models and distributed models employed in transmission-line theory are more appropriate. However, a full field theory approach provides a complete 3D formulation of the electromagnetic fields. As a result, numerical methods that provide rigorous field theory solutions to Maxwell's equations for arbitrary 3D geometries are crucial in the design of RF systems.