You can do with js option:
'source'=>'js: function(request, response) {
$.ajax({
url: "'.$this->createUrl('campaign/autocompleteTest').'",
dataType: "json",
data: {
term: request.term,
tag: $("#tag_id").val()
},
success: function (data) {
response(data);
}
})
}',
Edit:
foreach ($tag as $t)
{
$res2 = explode(',',$t);
$res = array_merge($res,$res2);
}