While the U.S. Navy says the “critical technologies” for the service’s proposed Air and Missile Defense Radar (AMDR) are “expected to be nearing maturity and demonstrated in a relevant environment” before the Navy has to make vital decisions about the program, those technologies are “currently immature,” the U.S. Government Accountability Office (GAO) notes in its recent update on major Pentagon programs.

The critical technologies that still need work include digital beamforming and transmit-receiver (TR) module development. Contractors say these are key to the success of AMDR, the anchor radar suite for the Navy’s and nation’s plans for maritime and coastal ballistic missile defense, in the U.S. and abroad.

AMDR will consist of an S-band radar for ballistic missile defense and air defense, X-band radar for horizon search, and a radar suite controller that controls and integrates the two radars. GAO estimates the program cost to be $15.2 billion, which includes about $1.6 billion for research and development and about $13.6 billion for procurement of about 24 units.

“Program officials stated that digital beamforming technology—necessary for AMDR’s simultaneous air and ballistic missile defense mission—has been identified as the most significant challenge and will likely take the longest time to mature,” GAO notes in its report. “Digital beamforming enables the radar to generate and process multiple beams simultaneously, which results in more radar resources being available to support simultaneous air and missile defense.

Program officials stated that this technology has been used before, but it has never been demonstrated in a radar as large as AMDR. Contractors have been working for some time to develop faster and more efficient TR modules, and GAO takes note of some of those efforts—and the remaining hurdles.

“The AMDR’s transmit-receive modules—the individual radiating elements key to transmitting and receiving electromagnetic signals—also pose a challenge,” GAO reports. “According to the program office, similar radar programs have experienced significant problems developing transmit-receive modules, resulting in cost and schedule growth.”

To achieve the increased performance levels required for AMDR, GAO says, the contractor will likely use gallium nitride semiconductor technology instead of the legacy gallium arsenide technology. Contractors have been touting their work with gallium nitride technology.

“The new technology has the potential to provide higher power and efficiency with a smaller footprint,” GAO acknowledges. “According to the Navy, this would reduce the power and cooling demands placed on the ship by the radar.”

However, gallium nitride has never been used in a radar as large as the AMDR, GAO points out, and the long-term reliability and performance of this newer material is unknown.

“If these transmit-receive units cannot provide the required power,” GAO cautions, “the program would either need to use the legacy technology and increase the power and cooling resources available for the AMDR, or accept reduced power and performance for the AMDR S-band radar.”

The Navy plans to install AMDR on Flight III DDG-51s starting in 2019. But, GAO notes, the Navy has determined the destroyer can only handle a 14-ft. active radar while the service needs a 20-ft. radar for integrated air-and-missile-defense requirements.