I added the following in parent page which will be called when the popup window is closed, which in turn populates the grid with the data added from the popup window
<asp:button id="btnHidden" runat="Server" style="display:none" onclick="btnHidden_Click" xmlns:asp="#unknown" />
Javascript code in popup window
function RefreshParent() {
window.opener.document.getElementById('cphPage_btnHidden').click();
window.close();
}
this solves all my problem