Question: Change range of "r" in polar plot

Hi,

First of all, I am wondering if this is even possible or even generally used... Maybe what I'm trying to do is not defined or whatever... I dunno.. But I'm gonna ask anyway.


What I want is to make a polar plot, with a different range.

I have a function r(a) which obviously calculates some radial distance as a function of the angle a.

I have so far found 2 ways to plot this in a polar graph:
with(plots):
plot(r(a), a=0..Pi, coords=polar)
polarplot(r(a), a=0..Pi)

(Where a is the angle)

These both give me the same polar graph which seems to be fine.
I can set the range of the angle just fine.


Now, I also want to set the range of r.
So I tried to plot the following:

plot(r(a), a=0..Pi, r=0.2..0.4, coords=polar)

Result, the "y-axis" (between " because you can't really speak of an y-axis anymore in polar graphs, but it's still there for some reason) is nicely limited from 0.2 to 0.4.
The "x-axis" however, is NOT!?

For some reason, it is only putting the range on the vertical direction, not in the horizontal direction?!


How can I make a plot where r ranges from 0.2 to 0.4 for example, in both directions???

Thanks!