如何使用knack API获得月度记录？

Using https://www.knack.com/developer-documentation/ getting the records by filters.But i stucked to get monthwise records.I have following demo which provide last 1 month records.but which operator i need to use to get monthwise records

$data = [
          [
            'field' => "field_28",
            'operator' => 'is during the previous',
            'range' => 1,
            'type' => 'months'
           ]
        ];

        $url= 'https://api.knack.com/v1/objects/object_1/records?filters='.rawurlencode(json_encode($data));