first you calculate the inner , outer diameter and dielectric constant of the dielctric material from the well established formula
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after that first you define the outer cylinder of the desired outer diameter with the know dieletric properties after that create another cylinder of inner diameter of PEC material and then insert it in the previous one and then assign the port.
hai herewith i have attached the datasheet for 174u coax cable u need to simulate the cable with shielding, jacket is not needed. define the shield as a ground