angularjs resource pass an array of object parameter but is null in api controller

I have an angularjs resource as seen below:

  return $resource('/api/report',
     { },
     {
       save: { method: 'POST', url: '/api/fileupload/savefile', isArray: false },
     });

My angularjs controller that uses this resource is below:

$scope.save = function () {
            var reportFieldsSample = [{ Field: 'ff', Value: 'gg' }, { Field: 'aa', Value: 'dd' }];
            Report.save({ reportParams: reportFieldsSample},
                { },
                function (content) {
                    console.log(content);
                });

My WebApiConfig for this route is:

   config.Routes.MapHttpRoute(
        "SaveFile",
        "api/fileupload/savefile",
        new { controller = "FileUpload", action = "SaveFile" },
        new { httpMethod = new HttpMethodConstraint("POST") });

My mvc api controller that receives this is below:

[HttpPost]
public HttpResponseMessage SaveFile(IList<Parameter> reportParams)
    {
        //reportParams is null
    }

Parameter class is declared in this way:

public class Parameter
{
    public string Field { get; set; }
    public string Value { get; set; }
}

The request enters my api controller but the reportParams argument of the controller is always null. Can you help me point out the problem? Thanks