C# - Page Still Refreshes After Wrapping The Repeater In An Update Panel

I've two SqlDataSources and two Repeaters, each repeater contains one hyperlink (i also tried using web server button and anchors). The hyperlinks fetch from the database some values and in the NavigationUrl property I use a string.Format method to create a parameterized url, to pass for the browser, then second repeater is populated according to the value passed in the url which is originally passed by the first repeater's hyperlink. this is my sample code : [URL]

<asp:ScriptManager id="Scrptmanagr" runat="server"></asp:ScriptManager>
<asp:UpdatePanel id="updtpanl" runat="server">
<ContentTemplate>
<asp:SqlDataSource ID="SqlDataSource1" runat="server" ConnectionString="<%$ ConnectionStrings:testConnectionString %>"
SelectCommand="SELECT [arrange_by_id], [arrange_by] FROM [arrange_by]">
</asp:SqlDataSource>
<asp:Repeater ID="Repeater1" runat="server" DataSourceID="SqlDataSource1">
<ItemTemplate>
<asp:HyperLink ID="HyperLink3" NavigateUrl='<%# string.Format("{0}?SortingType={1}",Request.AppRelativeCurrentExecutionFilePath, Eval("arrange_by_id"))%>' runat="server"><%# Eval("arrange_by") %></asp:HyperLink>
</ItemTemplate>
<SeparatorTemplate>
|
</SeparatorTemplate>
</asp:Repeater>
<asp:SqlDataSource ID="SqlDataSource2" runat="server" ConnectionString="<%$ ConnectionStrings:testConnectionString %>"
SelectCommand="SELECT [alphabet_id],[arrange_by_id], [value] FROM [alphabet] WHERE ([arrange_by_id] = @arrange_by_id)">
<SelectParameters>
<asp:QueryStringParameter Name="arrange_by_id" QueryStringField="SortingType" Type="Int32" DefaultValue="1" />
</SelectParameters>
</asp:SqlDataSource>
<br /><br />
<asp:Repeater ID="Repeater2" runat="server" DataSourceID="SqlDataSource2">
<ItemTemplate>
<asp:HyperLink ID="hyper1" runat="server" NavigateUrl='<%#string.Format("{0}?SortingType={1}&SortBy={2}",Request.AppRelativeCurrentExecutionFilePath, Eval("arrange_by_id"),Eval("value"))%>'><%# Eval("value")%></asp:HyperLink>
</ItemTemplate>
<SeparatorTemplate>
|
</SeparatorTemplate>
</asp:Repeater>
</ContentTemplate>
</asp:UpdatePanel>

Now! everytime I click any of the hyperlinks it causes a full post back and refreshes the page!