I no longer need help with this, I just figured it out on my own.
The reason r=1 didn't work was because "the inputs must be vectors with equal length or matrices with equal size." So I had 100 angles from 0,pi/2 but only 1 radius.
For anyone who may be caught in a similar situation, the following code fixed the issue.
t = linspace(0,pi/2,100);
r = ones(100,1);
hold on;
polarplot(t,r,'LineWidth',4);
hold off;
However, I would still like to know if it's possible the simply change the thickness of the original border. I would much prefer that option as opposed to adding another element to the plot.
Best Answer