Hello - I’m looking into the use of the BEMPP tool for planar (PCB) antenna applications with the Maxwell (electromagnetic) boundary conditions that include multiple feed ports. I’ve found the examples that demonstrate the use of what is described in some places as a voltage delta-gap source to excite the structure and I can get reasonable-looking far-field patterns from a single-port patch antenna. I’m still not clear on the exact physical model of assigning a value to the RHS of the equation (it is referenced in several examples as a voltage - is that a voltage / E-field value across the edge / between the centers of the two adjacent cells? Relative to a global ground? The former seems more in agreement with the scattering examples, but harder to use properly as an excitation)

I want to try simulations of a dual-polarized patch antenna, which requires multiple feed points at different locations that need to be excited separately. This same problem would come up with multi-port microwave / microstrip / stripline structures, as well.

The typical way to handle multiple feed ports is to induce power / field / voltage at one port location, and replace the port at the second location with a matched load (i.e., 50 ohm lumped or equivalent resistance) and measure the induced voltage and current through that load to determine the coupled power. The problem is then solved once for each port and the final coupling matrix determined. So, I’m looking for a way to model a lumped or distributed resistance (impedance) in BEMPP.

A lumped resistance would be simplest. In many MoM solvers, it is (conceptually) straightforward to add additional factors in the coupling matrix that can link different RWG cells to allow this kind of coupling to be represented. I haven’t seen any discussion in the documentation or the forum that discusses this option, and I’ll admit that my dives through the “core” assembler codes to try to understand the data structure and confirm the particular form of the physics equations in use have not been enlightening.

A distributed or effective resistance would work also - define a bridge in the mesh between two structures, and assign an effective surface resistance for the strip that equates to the target 50 ohms. I can’t find any discussion or documentation that describes anything other than a dielectric-dielectric boundary or a dielectric(vacuum)-PEC boundary.

I believe that doing what I want (getting a lumped/distributed impedance) requires a change to the LHS, not the RHS of the equation. Does anyone have any recommendations? Or, am I overthinking this, and I should be able to pull the port-port coupling numbers I want straight from the standard RHS A matrix? Thank you!