Download in Null

I recommend you use PHPExcel link

Your call should be like this:

function downloadExcel(status)
{
    url = "http://localhost/WareHouse/reporte.php?status="+status;
    window.open(url,"_blank"); 
}

And your PHP file something like this:

<?php
/** Error reporting */
error_reporting(E_ALL);
ini_set('display_errors', TRUE);
ini_set('display_startup_errors', TRUE);
date_default_timezone_set('America/Mexico_City');//Change to your location

if (PHP_SAPI == 'cli')
die('This example can be run only in web browsers');

/** Include PHPExcel */
require_once dirname(__FILE__) . '/Classes/PHPExcel.php';

// Create new PHPExcel object
$objPHPExcel = new PHPExcel();

// Set document properties
$objPHPExcel->getProperties()->setCreator("StackOverFlow")
                         ->setLastModifiedBy("StackOverFlow")
                         ->setTitle("Office 2007 XLSX Document")
                         ->setSubject("Office 2007 XLSX Document")
                         ->setDescription("Document for Office 2007 XLSX, generated using PHP classes.")
                         ->setKeywords("office 2007 openxml php")
                         ->setCategory("Result file");
require_once('apis/connection.php');
if(isset($_GET['status']))
{
  $status = $_GET["status"];
  //Trae todos los item que esten por debajo de su minimo en stock.
  $connection = new MySqlServerConnection();
  $query = "SELECT i.description_item,i.quantity,u.name_unit,i.reorder_Level,i.target_Stock,l.name_location,i.commentt,io.quantity_s,i.status
  FROM inventory_list AS i
  INNER JOIN unit_mesurement AS u ON id_unit = fkUnit
  INNER JOIN location AS l on id_location = fkLocation
  INNER JOIN inventory_output as io on id_output = fkInventory
  WHERE i.quantity <= i.reorder_Level OR i.status = 1";
  $result = $connection->executeQuery($query,array($status));
  if ($result > 0)
  {
      $objPHPExcel->setActiveSheetIndex(0)->setCellValue('A1', 'Description');
      $objPHPExcel->setActiveSheetIndex(0)->setCellValue('B1', 'Quantity');
      $objPHPExcel->setActiveSheetIndex(0)->setCellValue('C1', 'Usage');
      $objPHPExcel->setActiveSheetIndex(0)->setCellValue('D1', 'Name Unit');
      $objPHPExcel->setActiveSheetIndex(0)->setCellValue('E1', 'Reorder Level');
      $objPHPExcel->setActiveSheetIndex(0)->setCellValue('F1', 'Target Stock');
      $objPHPExcel->setActiveSheetIndex(0)->setCellValue('G1', 'Area');
      $objPHPExcel->setActiveSheetIndex(0)->setCellValue('H1', 'Comment');


      $arraycount=count($result);
      $i=0;
      $total=0;
      while ($i < $arraycount)
      {
        $j=$i+2;
        $objPHPExcel->setActiveSheetIndex(0)->setCellValue('A'.$j, $result[$i]['description_item']);
        $objPHPExcel->setActiveSheetIndex(0)->setCellValue('B'.$j, $result[$i]['quantity']);
        $objPHPExcel->setActiveSheetIndex(0)->setCellValue('C'.$j, $result[$i]['quantity_s'];);
        $objPHPExcel->setActiveSheetIndex(0)->setCellValue('D'.$j, $result[$i]['name_unit'];);
        $objPHPExcel->setActiveSheetIndex(0)->setCellValue('E'.$j, $result[$i]['reorder_Level'];);
        $objPHPExcel->setActiveSheetIndex(0)->setCellValue('F'.$j, $result[$i]['target_Stock'];);
        $objPHPExcel->setActiveSheetIndex(0)->setCellValue('G'.$j, $result[$i]['name_location'];);
        $objPHPExcel->setActiveSheetIndex(0)->setCellValue('H'.$j, $result[$i]['commentt'];);
$i++;
        }
    }
}

// Rename worksheet
$objPHPExcel->getActiveSheet()->setTitle('Result');


// Set active sheet index to the first sheet, so Excel opens this as the first sheet
$objPHPExcel->setActiveSheetIndex(0);


// Redirect output to a client’s web browser (Excel5)
$nombre=date("d-m-y H:i");
header('Content-Type: application/vnd.ms-excel');
header('Content-Disposition: attachment;filename="Reporte_'.$nombre.'.xls"');
header('Cache-Control: max-age=0');
// If you're serving to IE 9, then the following may be needed
header('Cache-Control: max-age=1');

// If you're serving to IE over SSL, then the following may be needed
header ('Expires: Mon, 26 Jul 1997 05:00:00 GMT'); // Date in the past
header ('Last-Modified: '.gmdate('D, d M Y H:i:s').' GMT'); // always modified
header ('Cache-Control: cache, must-revalidate'); // HTTP/1.1
header ('Pragma: public'); // HTTP/1.0

$objWriter = PHPExcel_IOFactory::createWriter($objPHPExcel, 'Excel5');
$objWriter->save('php://output');
exit;

I have not tried it, please tell me if it worked.

I usually use ajax to call things this way, and I know that it has ever failed me because I was missing the cache , contentType , processData ... Although in your case it's get, I'm not sure if it changes anything.

$.ajax({ url: url,
        type: 'post',
        success: function(output) {
            console.log(output);
        },
        error: function(salida) {
            console.log(salida);
        },
        data: formData,
        cache: false,
        contentType: false,
        processData: false,

    });

I also usually make calls in this other way:

var request = new XMLHttpRequest();
var formData = new FormData();
request.onreadystatechange = function() {
    if (request.readyState == XMLHttpRequest.DONE) {
        var response = request.responseText;
        console.log(response);
    }
};
request.open('POST', url);
request.send(formData);