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The FEM current source and complex load for the FEM region enables the setting of an excitation inside a FEM dielectric region and to calculate S-parameters.
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. Consider the cavity backed patch antenna below from .The patch is fed with the FEM current source and a 50 Ohm load is placed at the load position. In both cases a “FEM line port” is created in CADFEKO. Subsequently a FEM current source is placed on one of the ports and a load on the other port.
The FEKO result for the input resistance vs. the reference result is shown below.
Figure 2: Comparitive results for input impedance
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.
 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.
Patch antenna with FEM 6.1
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