Spacing between metal sheet and dielectric radome for best RCS

[Silvester]

TL;DR

Determine the spacing between metal sheet and dielectric radome to achieve best RCS for various incident and reflection angle.

I'm working on a project about designing a radome for a reflector/scattering object like RIS or reflectarray. I run simulations on HFSS. For simplicity and the purpose of seeking regularity, i start with a dielectric radome(with relative permittivity = 3) and copper sheet.

Suppose that (1)large incident and reflection angle extends the length of propagation, and (2) higher RCS comes from the constructive interference. this problem should be easy to conquer after some simulations are done.

it turns out that as the incident angle increases, the spacing needed to have maximum RCS also increases, and peak or minimum RCS repeats with the period of half-wavelength/cos(theta) , corresponding to the wavelength of oblique angle.

but i can't figure out what spacing would the first peak show up.
i doubted it's about phase (constructive/destructive interference), but HFSS incident plane wave does not allow user to see the phase. i have written a MATLAB script to calculate the phase using transmission line analogy, the calculated phase does not match the HFSS result.

 

[Dale]

What are RCS, RIS, HFSS

 

[renormalize]

For simplicity and the purpose of seeking regularity, i start with a dielectric radome(with relative permittivity = 3) and copper sheet.

What is the shape of the "radome"? Is it a flat sheet of dielectric? If so, what is the sheet thickness?

Suppose that (1)large incident and reflection angle extends the length of propagation,

What is meant by "extends the length of propagation"?
And does this reflector have to work at only one wavelength or is there a finite bandwidth?
Finally, are you familiar with "Salisbury screen" radar absorbers? These can be made into reflectors by altering the spacing of the components. The absorptive/reflective properties of such structures can be worked out with just pencil and paper, no finite-element simulators like HFSS required.

 

[Silvester]

What is the shape of the "radome"? Is it a flat sheet of dielectric? If so, what is the sheet thickness?

What is meant by "extends the length of propagation"?
And does this reflector have to work at only one wavelength or is there a finite bandwidth?
Finally, are you familiar with "Salisbury screen" radar absorbers? These can be made into reflectors by altering the spacing of the components. The absorptive/reflective properties of such structures can be worked out with just pencil and paper, no finite-element simulators like HFSS required.

Hi, renormalizer:
It's glad to see your reply and i appreciate it. Also, i'm from Taiwan so English is not my mother tongue, i apologize for imprecise wording.

By saying length of propagation, when the distance between radome and copper sheet is fixed, noted as spacing (S), consider EM-Wave as rays. As these parallel rays incident with oblique angle theta, the length of the ray's path is no longer S but S/cos(theta), which is extended.

The shape of the radome is also a thin square sheet. The copper sheet is set 432mm x 432mm, 3mm thick, the radome side length is set 432+3.5*spacing so that no electromagnetic wave would touch the copper without passing through radome (i knew it's infeasible to implement, it's just for research).

As for the thickness, at first i use 3mm as thickness. However, i realized that 3mm is thick enough to provide about 30 degree phase shift, so i change the thickness to 0.1 mm.

My goal is not making it broadband, so single frequency/wavelength is fine. As for Salisbury Screen, i will spend some time to check it out.

Thanks.