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How to design the lengths of Though,Reflect, line?

Question asked by hustcao on Aug 23, 2007
Hello,I have some problems about on-wafer TRL calibration on measurement of microwave properities of BaSrTiO3 Thin Films using the CPW(Corplanar waveguide) transmission lines.
      BaSrTiO3  is a kind of ferroelectric meterials having the character of high dielectric constant (50-300) which can be changed by the applyed DC bias.
I want to measurement the dielectric constant,loss tangent and tunability of BST thin film using CPW transmission lines like Fig 1 in the  the attached schedule at frequence of 10GHz..
       The characteristic impedance  of CPW  connecte with the BST's dielectric constant , so it cann't achieve impedance matching to 50 ohm before measurement,so we must using TRL alibration like Fig 2 in the  the attached schedule to de-embedding the S21coefficient of CPW.
        My problem is how to design the lengths of Though,Reflect, line? what is the general principles about these?And the cone-shaped  parts between the probe pads and transmission lines is a transition of impedance,How to design the probe pads to satisfy 50 ohm matching with the probes and how to design the lengths of  transition parts and probe pads ?
       Look forward to you reply soon,thanks.[/D:\Microsoft Word file (2).rtf]