As Jinfeng suggested, there might be an overlapping of the port and the PEC bodies of your dipole. I simply suggest you clear your already-defined ports, and pick the two edges of your dipole antenna by pressing the "E" button on the keyboard. After you pick the edges, you can go on an click on the discrete port section. In this way, the port will be perfectly aligned with the two PEC edges.

Dear Jinfeng Li and Omid Niksan thanks for your reply exactly, I made some changes in background properties and boundry conditions then the simulation went well.