This is a demo tutorial. While there is no step-by-step commentary available (yet), the live demo below is fully functional. Feel free to open it for full source code.
This demo shows how we can use radius and innerRadius adapters to create partial-radius axis ranges / fills on a RadarChart.
See the Pen amCharts 4: Partial axis ranges on a RadarChart by amCharts team (@amcharts) on CodePen.24419