var mein_fenster;
	function open_popup(url, width, height){
		var center_left = (screen.width-width)/2;
		var center_top = (screen.height-height)/2;
		//window.open(url, name, features)
		mein_fenster = window.open(url, "name_des_fensters", "width=" + width + ", height=" + height + ", left=" + center_left + ", top=" + center_top + ", toolbar=no, menubar=no, location=no, directories=no, status=no, scrollbars=no, resizable=no, fullscreen=no");
		mein_fenster.focus();
	}