// this is the handle for the popup window
var date_popup;

// this function does the popup
function calendar(control_obj,control_name) {

  URL  = '/util/calendar/popup.phtml?current=' + control_obj.value;
  URL += '&control='+control_name;
  
  if(! date_popup) {
    date_popup = window.open(URL,"Calendar_Popup","height=300,width=300,location=no,menubar=no,toolbar=no,scrollbars=yes,resizable=no,dependent=yes");
  } else {
    date_popup.focus()
    date_popup.location = URL;
  }
}