pdeModeler is for 2-D problems, so I assume that you have 2-D geometry. In this case, you can use a parametrized function for 2-D geometry creation.
You can also use CSG modeling in the pdeModeler app, using an ellipse as one element.
![ellipses.png](https://www.mathworks.com/matlabcentral/answers/uploaded_files/206133/image.png)
Alan Weiss
MATLAB mathematical toolbox documentation