A defence radar system costing nearly $2 billion has failed to detect any of the more than 200 asylum seeker boats that have landed on Australian shores in the past two years, a report said Sunday.

Under a front-page headline "Border Radar Fiasco", the Sun-Herald said the Aus$1.8 billion (US$1.9 billion) Jindalee Operational Radar Network (JORN) was only able to detect vessels equivalent to an Armidale class patrol boat.

The Armidale, which is used by the navy, is 56 metres long (183 feet) and has a displacement of 270 tonnes.

It means the system is not alerting authorities to the often small, rickety boats that have ferried thousands of asylum seekers to the country on well-worn routes from Indonesia.

This is despite successive governments in Canberra promising over the past decade that JORN would detect people-smuggling and illegal fishing boats, which are typically about nine to 15 metres (29-49 feet) in length, the report said.

"The (radar) is expected to detect objects on the surface of the water that are equivalent in size to an Armidale class patrol boat or larger," a Customs and Border Protection spokeswoman told the newspaper.

"The ability to detect surface objects smaller than this is highly improbable based on one or more factors including object size, construction, prevailing ionospheric and environmental conditions."

As a consequence "no sightings of suspected irregular entry vessels have been passed on to Customs and Border Protection," the spokeswoman said.

According to Department of Immigration figures, 220 "suspected irregular entry vessels" have landed in Australia since January 2009.

Asylum seeker boats are often intercepted close to land by Customs ships that operate their own smaller radar systems.

JORN consists of land-based radars in Western Australia, Alice Springs and Queensland and can monitor air and sea movements across 37,000 square kilometres (14,300 square miles), according to the Sun-Herald.