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Without knowing anything resembling specifics: (most) antennas are senseable -- they absorb a given frequency by design and ergo appear as 'black' when imaging a given spectrum.

Exceptions to (most) include plasma antennas, which can disappear on demand.

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Most antennas actually have a large radar cross section (RCS), with simple dipoles being some of the worst. An infinitely thin dipole (a current filament) has a non zero RCS even though it has no physical cross section.

In theory, a reflector antenna can have a zero RCS, so putting a reflector behind a dipole will reduce the RCS. It’s totally non-intuitive.

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