geocoding - Radius not calculated correctly in PHP

one text

I am calculating radius using this code :

function calculateRadius($lat1, $lon1, $lat2, $lon2, $unit) {
  $theta = $lon1 - $lon2;
  $dist = sin(deg2rad($lat1)) * sin(deg2rad($lat2)) +  cos(deg2rad($lat1)) * cos(deg2rad($lat2)) * cos(deg2rad($theta));
  $dist = acos($dist);
  $dist = rad2deg($dist);
  $miles = $dist * 60 * 1.1515;
  $unit = strtoupper($unit);
  if ($unit == "K") {
      return ($miles * 1.609344);
  } else if ($unit == "N") {
      return ($miles * 0.8684);
  } else {
      return round($miles,2);
  }
}

$radius=calculateRadius($lat1,$long1,$lat2,$long2,'K');

Now if i'm passing the same location to both the lat long parameter, then it is still returning 9.4930730546311E-5 as radius.