how to open window in new page on button click

hi all,
Here's my code
If rdvalue = "Dept" And ddldeptr.SelectedValue <> "" Then Button1.PostBackUrl = "~\Reports\Hrmis\CrvGpDept.aspx?fromd=" & txtfrom.Text & " &tod=" & txtto.Text & "&dep=" & ddldeptr.SelectedValue & "" ElseIf rdvalue = "Sect" And ddlsectr.SelectedValue <> "" Then Button1.PostBackUrl = "~\Reports\Hrmis\CvGpSect.aspx?fromd=" & txtfrom.Text & " &tod=" & txtto.Text & "&sec=" & ddlsectr.SelectedValue & "" ElseIf rdvalue = "Desig" And ddldesigr.SelectedValue <> "" Then Button1.PostBackUrl = "~\Reports\Hrmis\CrvGpdesig.aspx?fromd=" & txtfrom.Text & " &tod=" & txtto.Text & "&desi=" & d ...