Why microstrip width (impedance) is rarely have smooth change, rather stepped?

[Terminator3]

My first guess was layout software problems: most of them have no such functionality, you must draw such line using thin lines, fill with something. Stepped line width is very simple. Second guess is that is easier to calculate, but...... with smooth change we have less discontinuity, so it can be wrong that stepped line width change is easier to simulate/model/calculate. Third guess: it is just a tradition.
Also maybe difference is too small to make it smooth, and just simplier to make it stepped.
Although, through googling on microwave companies websites, i see some photos of microstrip PCB's with smooth width changes, wich i am interested in: can i replace stepped width with the smooth one, wich angle is best? For antennas, there are some exciteing designs that use radial stubs of different sizes to vary power distribution between several microstrips. Can it be done only by simulation, or there are some ready to use application notes exists and it can be calculated?

 

[afz23]

There are several methods used to join
to unequal widths.
Chebyshev multisection method,
Tapered line using exponential,triangular
and klopfenstein taper.

All these methods require additional space
on PCB,increasing board size.

So designer should decide whether he
can sacrifice power due to step discontinuity
or increase board to accommodate taper.

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Modern simulation softwares have both step as
well as tapered junctions as there standard
components.