That is a halftone - is it not, viewed in Photoshop in bitmap mode? You will need to view at 100 or 1:1 view in Photoshop if this image does contain bitmap halftones. Although 100% view is the safest, you may also find less artifacts in reduced views such as 50% or 25% than with an "odd" figure such as 11% etc. Any other reduced magnification will likely cause display issues. Radial gradients are very unforgiving. Linear gradients have less problems, however both are synthetic images that are perfect, so any curve will tend to cause issues. Natural images are not perfect in their gradation so have more leeway for error. You may still have problems on plate, however I would first guess that your plate curves are fine and this is just a display issue. Of course, you do have to test that your curves are not creating banding or other issues in gradients on plate and press.
Stephen Marsh
