How do I simulate the radiation pattern of an antenna using a full wave electromagnetic solver?

Simulating the radiation pattern of an antenna using a full-wave electromagnetic solver (HFSS, CST, FEKO) requires careful setup of the simulation domain, excitation, boundaries, and post-processing: (1) Simulation domain: the antenna model is placed in a simulation volume that extends at least lambda/4 beyond the antenna structure in all directions. This provides space for the near fields to develop before reaching the boundary. For electrically large antennas (D > 10×lambda): the simulation volume can be very large, requiring efficient solvers (MoM or asymptotic methods). (2) Boundary conditions: radiation boundary (ABC: absorbing boundary condition in FEM, open boundary in FDTD): allows outgoing waves to pass through the boundary without reflection. The boundary must be at least lambda/4 from the antenna (further is better for accuracy). PML (Perfectly Matched Layer): an absorbing layer that eliminates reflections at the boundary. PML is more accurate than simple ABC (typically < -40 dB reflection). PML is the standard in HFSS and CST. Ground plane: if the antenna is above a ground plane: model the ground plane as a perfect electric conductor (PEC). For infinite ground planes: HFSS supports an infinite ground plane boundary (eliminates the need to model a finite ground, which would generate edge diffraction). (3) Excitation: apply a wave port or lumped port at the antenna feed point. Wave port: excites the antenna with the dominant mode of the feed structure (microstrip, coax, waveguide). Provides accurate S11 calculation. Lumped port: a simplified port model (a voltage or current source across a gap). Faster to set up but less accurate for S11. (4) Far-field computation: after solving the near fields: the solver computes the far-field radiation pattern by: HFSS/FEM: integrating the equivalent currents on a closed surface surrounding the antenna (the radiation boundary). Using the near-to-far-field transformation. CST/FDTD: transforming the time-domain near fields to the frequency domain, then applying the near-to-far-field transformation. FEKO/MoM: directly computing the far field from the surface currents on the antenna. (5) Results: the radiation pattern is plotted as: gain (dBi) vs angle (theta, phi), in 2D cuts (E-plane, H-plane) or 3D surface plots. From the pattern: the main beam direction, beamwidth, sidelobe levels, front-to-back ratio, and directivity are extracted.