The MATLAB routines for plotting curves instead of straight lines are:
- viscircles() (Image Processing Toolbox)
- rectangle() (basic MATLAB) -- despite its name, you can create ovals and circles from it
- scatter() or plot() with markershape 'o' and large marker size
The other routines all plot straight lines (and the above may internally create straight lines.)
It is very unlikely that your display can plot actual curves. If it were the early 1980s then you might have had a Tektronix 4010 or 4014 which could plot curves. Even now, some air traffic controllers and military radar sites apparenlty use specialized displays that have an seperate overlay that can draw curves. If you are displaying onto a 1960's CRT, then Yes, you just might be able to draw curves.
But if you are using any display since the early 1980s and you are not using a very very expensive radar display, then chances are very high that you are using a display that is entirely pixelized, individually addressible dots with fixed position.
The trick is that if you plot a lot of adjacent small straight lines, then it can look like a curve, especially if anti-aliasing is on.
... But to do that, you have to pass MATLAB data that is sufficiently dense that when it is represented as pixels, it looks curved.
If you do not have the extra points yet, but you have a model of how the curve should look, then polyfit() with polyval(), or spline() with ppval(), or interp1() with various options, can help create intermediate points.