UTD for dielectric coated PEC plate
I applied dielectric coating to PEC plate and computed nearfield results using UTD and MoM. Thickness of the layered dielectric was set to be lambda/200. Result obtained by UTD for observation points in spherical coordinates with theta>70 deg looks identical to result obtained from a PEC plate. I have attached the result figure and feko model files. Can you please comment on the result.
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Answers
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Hi @shan25,
I gues this is due to the UTD formulation in the shadow area. For a larger plate (e.g. 40x40 lambda) the effect will show up for Theta >90° only which is the shadow region here. Please note, 4x4 lambda is extremely small for an asymptotic method like UTD.
I will wait for further info from the developer and then let you know.
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Hi @shan25,
The feedback from the developmet:
This is the expected behaviour, as for UTD the effect of coatings is only taken into effect for the reflected rays (there are no transmitted rays here for a PEC plate backed with a coating, but even for a transparent TDS sheet there are no direct rays in the current UTD formulation - this is well documented and also I believe the Feko solver will give a warning).
In the shadow region, the only contributions to the fields are edge and corner diffracted rays, and for these, always the PEC formulas are used, i.e. if you add a coating to the plate or not will indeed not have any impact on the field in the shadow region, and also in fact not in the region where there is no reflected ray, only the incident rays (i.e. between the ISB - incident shadow bounday - and RSB - reflection shadow boundary).
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Hi Torben,
I was expecting this answer. As the wedge and corner diffracted fields from feko were predicting fields as if the plate is of PEC type. You can convey to feko developer that for a homogeneous dielectric slab/coating UTD wedge and corner diffracted formulates can be easily modified. It also seems to me that UTD corner diffracted formulations implemented in feko is based on this paper 'First-order equivalent current and corner diffraction scattering from flat plate structures'. This formulation is not accurate I noticed it when comparing UTD results with MoM.
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Thanks @shan25!
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