What you want is probably a 3D widget. So instead of HUD I’d make a widget and then put the widget on an actor that you can place it in 3D space.
Here’s a tutorial. They don’t call it “radar”, they call it “mini map” but it’s actually nearly the same. Just look at the part where they create the widget with TextureRender2D and you’ll understand how they actually do it. Didn’t look at your radar HUD, but i think it can be converted rather easily.