Hello Mustafa,
In general for a Radar chart you have to create the radial axes yourself and add them to the chart. You have access to the NAxis instances, because you create them. So the code for a single axis should be something like:
NRadarAxis axis = new NRadarAxis();
axis.Visible = true;
axis.View = new NRangeAxisView(new NRange1DD(0, 100), true, true);
radarChart.Axes.Add(axis);
You have to repeat that for each radial axis that you want to display.