APEX

i am using apex 18.1 with database 11g in windows, my page has dynamic action, with following Execute java script;

apex.navigation.redirect('localhost:1234/reports/rwservlet? server=servername.&report=myrep.rdf&userid=user/pwd@link&desformat=pdf&destype=cache&paramform=no');

it works fine when Button press but output (.pdf) opens in same browser tab and i do want it to open in new tab; please assist.
i did this, window.open('localhost:1234/reports/rwservlet? server=servername.&report=myrep.rdf&userid=user/pwd@link&desformat=pdf&destype=cache&paramform=no','_blank'); but  it behaves same and opens it in same windows and tab