Drawing a circle

Hi.

I need to draw a circle whit center (a,b) and radio r. So I use the
R code below

a<-1.975 # valore x del centro
b<-1.215 # valores y del centro
r<-1.46 # radio
x1<-seq(a-r,a+r,by=0.01); #los valores de x
yp<-sqrt(r^2-(x1-a)^2)+b; # los valores y a partir de la ra??z positiva
yn<-(-1)*sqrt(r^2-(x1-a)^2)+b; # los valores y a partir de la ra??z negativa
x<-c(x1,x1);  y<-c(yp,yn);

plot(x,y,type="l",ylab="",xlab="",xlim=range(x),ylim=range(y));


My circle have two problems.

First. I don't want the horizontal line and I don't know how avoid
it.

Second. It is shaped like ellipse. I need adjust the x and y scales,
but I don't know how.

Can you help me???

there is another way to draw a circle whit R ?