You may want to open a custom navigation menu link in a new window or a new tab for several reasons. For instance, if you have an external link in the menu, its a good idea to make sure that it opens in a new window.
Its really easy to force a custom menu link open in new window or tab. But to do it, you must first enable the Link Target functionality in custom menus. Go to Appearance > Menu, and click on screen options in the top right corner. Then check the Link Target option.
Now just open the menu item that you wish to open in a new window, and select New Window or Tab, from the Link Target drop down list.
That’s it. Save the menu and this link will open in new window or tab.