How do I properly setup a Characteristic Mode Analysis (CMA) solution of a Patch Antenna (w/Substrate medium included)?

Ricardo Sendrea

Hello!

I'm trying to solve CMA for a standard rectangular patch antenna. Specifically, I created a dielectric box (assigning the region a permittivity value of 4.4) with dimensions sub_length = 1, sub_width = 1, and sub_height = 1.56e-3, along X, Y, and Z, respectively. Next, I created a second dielectric box with dimensions patch_length = 0.5, patch_width = 0.5, and patch_height = 1.56e-3, along X, Y, and Z, respectively. Then, I clone the second box and subtract it from the first box. Now, I have two non-overlapping box structures, where I assign the top face of the second box a PEC boundary. Finally, I unite the two structures and assign the bottom face a PEC boundary.

I set my operating frequency as 300MHz and selected the characteristic mode solver for 10 modes. Unfortunately, the FEKO solver runs into an issue: 

ERROR 37590: The characteristic modes that were calculated are all non-radiating

Does anyone know how I can solve this problem in this FEKO version?

I am attaching the project file for more info.

Thanks!

Ricardo

Torben Voigt

Hi Ricardo,

Your model is very different from the model in Fig. 16 in the paper, both in terms of dimensions and dielectric properties. Therefore, I have rebuilt the patch from Fig. 16 and get very similar results. Unfortunately, I no longer have Feko 2020, so the model is from Feko 2023.1.2. 

One more comment: The way you created your model seems a little complicated to me. In principle, a cubuid and a rectangle are all you need. Pay attention to the correct assignment of the materials (substrate and PEC). If you leave the material of the patch defined as "default", it will otherwise become a dielectric boundary after Union. You must also assign PEC to the lower surface of the substrate.

I hope this helps!

Best regards,
Torben

Torben Voigt

Hi Ricardo,

Which version are you using? I remember getting this error many years ago, due to so-calles "fictious modes", but I think the Eigenmode solver has been improved since then. The workaround was increasing the nbumber of requested modes. Maybe this helps in your case, too?

Of not, could you attach your model?

Best regards,
Torben

Ricardo Sendrea

Torben Voigt_20420 said:

Hi Ricardo,

Which version are you using? I remember getting this error many years ago, due to so-calles "fictious modes", but I think the Eigenmode solver has been improved since then. The workaround was increasing the nbumber of requested modes. Maybe this helps in your case, too?

Of not, could you attach your model?

Best regards,
Torben

Hello Torben,

Thank you for the suggestion!

I was able to find a solution by increasing the requested number of modes. Unfortunately, I am not sure if these are correct, as the first two modes found are not what is expected (a vertical and horizontal current distribution along the patch surface). Instead, the solution seems to be dominated by the larger ground plane below. 

I'm using FEKO version 2020.0.0. I attached the model to the original post. 

I solved a similar patch antenna design (given in [1] see Figure 16.-17) in FEKO and acquired the same seemingly errorous modes found by FEKO discussed in the paper. Perhaps there is a proper way to setup the solution such that we see the expected patch modes?

[1] K. D. Paschaloudis, C. L. Zekios, S. V. Georgakopoulos and G. A. Kyriacou, "A Finite Element-Based Characteristic Mode Analysis," in IEEE Open Journal of Antennas and Propagation, vol. 3, pp. 287-303, 2022, doi: 10.1109/OJAP.2022.3150594

Link to paper: https://ieeexplore.ieee.org/document/9709591

Best,
Ricardo

Torben Voigt

Hi Ricardo,

Your model is very different from the model in Fig. 16 in the paper, both in terms of dimensions and dielectric properties. Therefore, I have rebuilt the patch from Fig. 16 and get very similar results. Unfortunately, I no longer have Feko 2020, so the model is from Feko 2023.1.2. 

One more comment: The way you created your model seems a little complicated to me. In principle, a cubuid and a rectangle are all you need. Pay attention to the correct assignment of the materials (substrate and PEC). If you leave the material of the patch defined as "default", it will otherwise become a dielectric boundary after Union. You must also assign PEC to the lower surface of the substrate.

I hope this helps!

Best regards,
Torben

Ricardo Sendrea

Torben Voigt_20420 said:

Hi Ricardo,

Your model is very different from the model in Fig. 16 in the paper, both in terms of dimensions and dielectric properties. Therefore, I have rebuilt the patch from Fig. 16 and get very similar results. Unfortunately, I no longer have Feko 2020, so the model is from Feko 2023.1.2. 

One more comment: The way you created your model seems a little complicated to me. In principle, a cubuid and a rectangle are all you need. Pay attention to the correct assignment of the materials (substrate and PEC). If you leave the material of the patch defined as "default", it will otherwise become a dielectric boundary after Union. You must also assign PEC to the lower surface of the substrate.

I hope this helps!

Best regards,
Torben

Hello Torben,

I had attached the original patch I had designed at 300 MHz. My design procedure was made complicated because I initially made a mistake when I tried creating a patch using just a cuboid and a rectangle. This mistake led to a meshing issue when I would run the mesher. Following your suggestion, I reran the design and I am seeing the mode distributions I was expecting.

Thank you for the help and swift replies!

Lastly, I think the errors I am seeing in regards to the paper results are due to my setup (number of modes requested, mesh and frequency sweep). Here, I used the default 'fine' mesh setting, and requested 20 modes, using a frequency step of 20 MHz.



Kind Regards,
Ricardo