Federal Government frontbencher Chris Evans has played down reports that Australia's Defence radar system is not detecting any asylum seeker boats.

Fairfax newspapers say the system, which cost nearly $2 billion, has not picked up any of the asylum seeker boats that have arrived in the last two years.

But Senator Evans has told Channel 10 the Government also uses other methods to detect boats, including aerial surveillance, not just the Jindalee Operational Radar Network (JORN).

"We have intercepted 99 per cent of the boats so the system is working. Jindalee's contribution to that is obviously something the Defence experts would have to comment on but I know the system's working because we are intercepting," he said.

"Jindalee is a very valued resource but it may not be the key resource in this battle against unauthorised wooden boat arrivals."

The Fairfax report claims the radar system is only able to detect vessels equivalent to an Armidale class patrol boat.

The Armidale, which is used by the navy, is 56 metres long 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 from Indonesia.

"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 Sun-Herald 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."

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, according to the Sun-Herald.

- ABC/AFP