default button not work for asp.net panel

Question

I have a aspx page that has a master page, in this page I have an asp.net panel and I want when I press enter search button fire,but it doesn't work. I test many solutions: set

this.Master.Page.Form.DefaultButton = this.btnAdd.UniqueID

but not worked,

set asp:panel defaultbutton,but it is not working,

set

this.Master.Page.Form.DefaultFocus = this.Mypanel.UniqueID

but not work... how can I solve this problem (without using jquery)?