Then you just left the comparison value blank. The code should be:
$searchRecordset2_1->setSearch(array("type"=>"Key", "comparison"=>"=", "join"=>"AND", "and"=>", ", "or"=>" ", "start_encap"=>"\"", "end_encap"=>"\""), array("ss_title", "ss_keywords"), "s", "".(isset($_GET["ss_keywords"])?$_GET["ss_keywords"]:"") ."");