function openPopup(targetField){
var w = window.open('booking_search_airports.html','color_popup','width=610,height=550,scrollbars=1');
w.targetField = targetField; //create target field variable in popup window with the passed targetField as value
w.focus();
return false;
}

//callback function
function setTargetField(targetField, returnvalue){
if (targetField){
targetField.value = returnvalue;
}
window.focus();
}