Try like that,
CABasicAnimation *pathAnimation = [CABasicAnimation animationWithKeyPath:@"path"];
[pathAnimation setFromValue:(id)[UIBezierPath bezierPathWithArcCenter:CGPointMake(self.view.frame.size.width/2 ,self.view.frame.size.height/2) radius:10 startAngle:0 endAngle:M_PI*2 clockwise:NO].CGPath];
[pathAnimation setToValue:(id)[UIBezierPath bezierPathWithArcCenter:CGPointMake(self.view.frame.size.width/2 ,self.view.frame.size.height/2) radius:radius*1.2 startAngle:0 endAngle:M_PI*2 clockwise:NO].CGPath];
[pathAnimation setDuration:15.0f];
[pathAnimation setRepeatCount:1.0f];
[pathAnimation setTimingFunction:[CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionLinear]];
circle.path = [UIBezierPath bezierPathWithArcCenter:CGPointMake(self.view.frame.size.width/2,self.view.frame.size.height/2) radius:radius startAngle:0 endAngle:M_PI*2 clockwise:NO].CGPath;
[circle addAnimation:pathAnimation forKey:@"changePathAnimation"];