Incident Power

Incident power for an antenna structure is defined as the time-averaged power incident on the port(s) of the antenna:

(1)

where

• P_inc is the incident power in watts.
• Re is the real part of a complex number.
• A is the union of all port boundaries in the model, including Wave and Lumped Ports, but excluding Floquet ports.
• E_inc is the incident electric field.
• H^*_inc is the conjugate of the incident magnetic field.
• dS is the local port-boundary unit normal directed into the 3D HFSS model.

In the Edit Sources window of a modal project, you specify the power as the magnitude of the Poynting vector along with the a phase specification for the complex modal excitation. The magnitude of the Poynting vector is computed from:

(2)

For a lossless port the incident power is the same as what is specified in edit sources. However, for lossy ports this is not true and therefore the incident power can be different from what is specified in edit sources.

In the Edit Sources window of a terminal project, you specify total voltage V instead of the modal incident power. Using the underlying modal S-matrix, HFSS converts the terminal excitation to total fields at the ports, and then applies the general definition. As a result of this procedure, the incident power in a terminal project depends on both the user-specified stimulation as well as the model itself.