<asp:LinkButton ID="LinkButton1" runat="server" target="_blank">LinkButton</asp:LinkButton>
Use target="_blank" because It creates anchor markup. the following HTML is generated for above code
<a id="ctl00_ContentPlaceHolder1_LinkButton1" target="_blank" href="javascript:__doPostBack('ctl00$ContentPlaceHolder1$LinkButton1','')">LinkButton</a>