jQuery Ajax序列化数据

First time I've attempted to use serialize data. On my main page when the submit button is clicked I'm running :

        $.ajax({
        url:'test.php?add=1',
        data:$(this).serialize(),
        type:'POST' })
        .done(function(data) { 
            console.log(data);
        })

On the test page I have :

if (isset($_REQUEST['add']) && $_REQUEST['add'] == '1' ) {
    var_dump($_REQUEST);
}

When I submit the form, all I get back in the console is:

array(2) {
  ["add"]=>
  string(1) "1"
  ["PHPSESSID"]=>
  string(32) "a9005002332f548a0c85b06402dfae12"
}

My form has about 30 fields, I thought I'd get the name and value of each field. eg: field1=value1&field2=value2&field3=value3

Normally when I've done this I've used:

        url:'test.php?add=1&field1=' + field1 + '&field2=' + field2,

etc.. which does return this data.

How do I get the values of the submitted data when using serialize ?

Thanks

$.ajax({
        type:"POST",
        url:'test.php',
        data:$("#myForm").serialize(),
        success: function(response){
            console.log(response);  
        }
    });

//on php page get data

if(isset($_POST)){ var_dump($_POST); }