javascript对象到json字符串到php数组 - > POST

Hey guys i really need help with this. i pass this json object to php..

var x = {};
x.xt = {};
x.xt.id = id;
x.xt.to = foo;

somearray.push(x);

convert object to json:

$.toJSON(x);

json string:

[{"x":{"xt":"9","to":"2"}}]

them i post this:

$.post(
    "temp/sop.php",
    { xa: somearray},
    function(data){
        console.log("response - "+ data);
});

server side:

$xtj = $_POST["xa"];
$encodedArray = array_map(utf8_encode, $xtj);
$asnk = json_decode($encodedArray);

This returns:

string(4) "null"

and this:

$asnk = json_encode($xtj);

returns:

null

the data base it is set to:

UTF8

also when i test if it is an array, comes back true..

any idea how to solve this? thanks

also server side:

$xtj = $_POST["xa"];
$asnk = json_decode($xtj);

this returns:

NULL