Ho risolto così:

codice:
var param = dataFrom=" + $("input[name=dataFrom]").val() + "&dataTo=" + $("input[name=dataTo]").val();;
var url = 'report_xls.php?' + param;


$.ajax({
    url: url,
    type: 'POST',
    success: function() {
        window.location = url;
    }
});

Grazie!