You can check these links,it may help you out.
- Distance Mapping with Radius Filter
- Creating a 50 mile radius around point
- Customers within N miles radius analysis using Tableau
hope it helps.
If you look up my "Indiana BMV Location Information" workbook on Tableau Public, blocked from here or I would paste it in, you can download the workbook and see how to create the radius circles. You are also welcome to send me questions via email or the forum and I will be happy to help.