Can somebody help me with exponential taper wideband balun?

I searched many papers ,and i found it is difficult to compute characteristic impedance of planar asymmetric lines which is air between them, it is very complex to construct exponential model, I cannot upload it here, can sombody help me? thx in advance!

you xan use autolisp codes in order to draw any equation by autocad. then you can import the structure by hfss and so on!