Modal Window Loses Focus when Tab and Shift+Tab is Pressed

Modal Window Loses Focus when Tab and Shift+Tab is Pressed

I'm Having a hard time Coding and Trying different approaches on how to
catch the tab and Shift+tab when Modal Window is open , It loses focus and
Jumps to Text box at the background ,
Can someone Help me with this situation. Thanks
editwindow = $("#modalWindow").kendoWindow({
title: "Edit Person Information",
modal: true,
visible: false,
resizable: false,
width: 600
}).data("kendoWindow");
Then
<div id="modalWindow" class="main">
@using (Html.BeginForm("Edit", "People", FormMethod.Post, new { id =
"PeopleForm" }))