Tapering of planar waveguides
Tapering to a reasonable degree is preferable to avoid sharp nodes for a VSWR mismatch. Now, if you taper for too long, then you just have a large amount of line that is a sub-optimal impedance. It really is a matter of what you're shooting for in terms of insertion loss/VSWR/space tradeoffs. I always consult the microwaves101 website for nice rules of thumb but I usually go 5-10% of a wavelength if I have the room. It looks like you have a good two step taper there but you haven't provided any sizing so I can't be sure.

Sometimes, the circuit might want a capacitive stub on either side of an inductive length such as this. 

Note: My experience tends to be in the 26 GHz and below range so please take my advice with a grain of salt.