Dear you can use this function in matlab Coaxial transmission line
Syntax
h = rfckt.coaxial
h = rfckt.coaxial('Property1',value1,'Property2',value2,...)
Description
Use the coaxial class to represent coaxial transmission lines that are characterized by line dimensions, stub type, and termination.
A coaxial transmission line is shown in cross-section in the following figure. Its physical characteristics include the radius of the inner conductor of the coaxial transmission line a, and the radius of the outer conductor b.
h = rfckt.coaxial returns a coaxial transmission line object whose properties are set to their default values.
h = rfckt.coaxial('Property1',value1,'Property2',value2,...) returns a coaxial transmission line object, h, with the specified properties. Properties that you do not specify retain their default values.