coolite tabpanel中gridpanel高度100%

RTtabpanel中有gridpanel，如何让gridpanel的高度等于tabpanel的高度？其中tabpanel里是iframe，iframe里面是gridpanel的页面。gridpanel结构如下：
 <ext:Toolbar ID="Toolbar1" runat="server">
                <Items>
 ..............
                 </Items>
 </ext:Toolbar>   <ext:GridPanel 
            ID="GridPanel1" 
            runat="server" 
            StoreID="Store1"
            StripeRows="true"
            AutoWidth="true"
            AutoHeight="true"
            Title="Company List"
            Header="false"
            AutoExpandColumn="username" 
            Collapsible="true">
            <ColumnModel ID="ColumnModel1" runat="server">          ..................
     <SelectionModel>
                <ext:CheckboxSelectionModel ID="CheckboxSelectionModel1" runat="server" />                   
            </SelectionModel>
            <BottomBar>
                <ext:PagingToolBar ID="PagingToolBar1" StoreID="Store1" PageSize="15"  runat="server" />
            </BottomBar>
        </ext:GridPanel>现在gridpanel是自动高度，这样分页控件就紧随gridpanel了，并不在最底下，很难看，如何才能让gridpanel填充整个tabpanel？