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A complex load impedance for the FEM region

The FEM current source (AF card) enables the setting of an excitation inside a FEM dielectric. The addition of the load (LF card) enables users to calculate S-parameters using the FEM current source.

This load is set at an arbitrary position inside the FEM mesh, i.e. it is not restricted to tetrahedral edges. The start and end points should coincide with metallic surfaces, but is not required to be at a mesh vertex. The length of the load should be much smaller than the wavelength.

Figure 1: Dialog for addition of a complex load in the FEM region
LF card dialog

Consider the cavity backed patch antenna below from [1].

Figure 2: FEKO model for cavity backed patch from [1]
Cavity backed patch model

The patch is fed with the FEM current source (AF card) and a 50 Ohm load is placed at the load position using the LF card.

The FEKO result for the input resistance vs. the reference result is shown below.


Figure 3: Comparitive results for input impedance
(a) FEKO
 (b) Reference result [1]
FEKO result missing
 Reference results from [1] missing<


One restriction is that this load should not be used as a short due to numerical instability. Users are advised to rather use a metallic strip to make a short.

References


[1] J. M. Jin and J. L. Volakis, “A hybrid finite element method for scattering and radiation by microstrip patch antennas and arrays residing in a cavity,” IEEE Trans. on Antennas and Propagation, vol. 39, pp. 1598–1604, Nov. 1991.