Why is there a disc darkening effect on Venus in the centimeter radio range? How should the physical conditions on the planet

Why is there a disc darkening effect on Venus in the centimeter radio range? How should the physical conditions on the planet be changed so that the opposite effect is observed – an increase in brightness towards the edge of the disk?

The darkening of the disc towards the edge indicates a hot surface of the planet, observed through the colder atmosphere. The opposite effect could be observed in the radio range if the planet had a hot ionosphere.

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