Open new window from code behind

Currently I am using below code to open a new window in my asp.net code behind.
When I click on that link at that time it opens  a new window. But after that whenever I click on that previous page, it will open a new window.
Below is my code.
ScriptManager.RegisterStartupScript(Page, Page.GetType(), "popup", "window.open('" + streditUrl + "','_blank')", true);

How do i solve this?
Thanks.