In this example, FDTD is used to simulate a X-band (WR-90) rectangular open-ended-waveguide-probe (OEWG) antenna mounted on a finite and infinite PEC ground plane. The radiation pattern and radiation efficiency are investigated using the Directivity Analysis group. This example demonstrates how the source window feature of the Directivity Analysis group can be used to accurately capture the total radiated power in instances the antenna's source (feed) passes through the directivity group's monitors.
The rectangular probe antenna is an aperture antenna used in RF applications such as in terrestrial communications and antenna measurements. Its widespread use is attributed to the antenna’s moderate bandwidth and gain, high-power capability, ease of integration with waveguide components, simple construction, and well-known near- and far-field response. Traditionally, a coaxial pin is used to excite the waveguide’s fundamental TE10 mode whose dominant field polarization and magnitude shown in the above figure. As with any aperture-type antenna, the generated fields on the open aperture are treated as the source of the far fields which are related to equivalent electric and magnetic current densities through field equivalence (Balanis ). In the case the probe antenna is mounted on an infinite ground plane, the radiation equation can be directly applied to find the theoretical far-fields. However, when the ground plane is finite, the far-fields must be approximated using diffraction theory or found numerically, such as in FDTD.
This example utilizes the directivity analysis group to find the radiation features of the rectangular probe antenna. First, the antenna is considered mounted on an infinite ground plane. Image theory is used to obtain the far-field FDTD and theoretical results which are then compared. Next, the antenna is considered mounted on a finite ground plane and FDTD results are presented.