Hello Samina,
Looking at your image it would appear that you have an arc waveguide as shown in the Analyzer. I am curious why you are not showing this design within the Designer, do you not have the original design file?
For reference I am attaching a screenshot of an arc waveguide with a start (0 um, 10 um) and end (800 um, 10 um) and a fixed negative radius of 4000 um which appears to give a similar qualitative look to your requested design.
Scott