Dhtmlxgrid filtering and sorting

I have a server side script which captures filter information:

    if (isset($_GET["dhx_filter"]))
      $filter = $_GET["dhx_filter"];

I use this data to compose the necessary where clause in this server side script.

The query composition and results fetched by this are as expected.

Now after the data has been fetched, I scroll down on the grid, in this event the dhx_filter comes empty, thus my logic doesn’t function. Is there a way to ensure dhx_filter’s persistance despite of the scroll event.