UESA Revival Offers Dual-Band Radar For Future Early Warning Aircraft

A small, Hawaii-based company hopes to support the next generation of airborne early warning aircraft by demonstrating an active, electronically scanned array with instantaneous, 360-deg. coverage inside a radome with a unique dual-band antenna.

North Star Scientific has demonstrated radar that shows 3-dB improvement compared to a first-generation ultra-high-frequency (UHF) band (400 MHz-1 GHz) electronically scanned array (UESA) tested by the U.S. Navy nearly 20 years ago, says co-founder Jim Stamm.

• Dual-band UESA shows 3-dB improvement
• U.S. Navy awards transceiver assembly contract

By coupling the UESA with an S-Band (2.3-3.7 GHz) antenna array, North Star believes the technology could revolutionize the airborne early warning (AEW) and airborne tracking mission for the U.S. Navy’s existing fleet of Northrop Grumman E-2D Advanced Hawkeyes—not to mention the respective Boeing E-3 Airborne Warning and Control System fleets for the U.S. Air Force and NATO or a future aircraft that could replace the Navy’s E-2D.

“A 3-dB change means you’ve basically doubled the radiated power,” Stamm says. “It doesn’t mean that you can see things twice as far away, because radar is a little more complicated than that, but it’s a substantial increase.”

A combination of the UESA with an S-band antenna could further improve performance. The UHF-band elements—supported by a 2D filtering technique called space-time adaptive processing—would provide early warning detection of even low-flying, stealthy aircraft against dense background clutter over land. Targets detected by the UHF-band element could then cue the shorter-wavelength S-band antenna to provide precise targeting at long range.

North Star has demonstrated an improvement in radiated power, but the company is still working on the integration of the interleaved, dual-band antennas.

“It has evolved into dual polarization for the S-Band, which is challenging to kind of shoot through the UHF band, so there’s still some work to be done,” Stamm says. “But the antenna, I would say, is 90% there.”

To support a potential retrofit program, North Star has designed the dual-band array to be compatible with the Lockheed Martin APY-9 radar on the E-2D. The Navy has been funding North Star’s work for a decade under a program called the High-Gain UESA radar, but Naval Air Systems Command (Navair) officials say they are not ready to commit to a retrofit program for the E-2D fleet or for a potential follow-on program.

“While the effort is making progress toward identifying improvements in performance over the existing antenna array, it is too early to project whether the technology will mature on a timeline that supports the incorporation onto the E-2D Advanced Hawkeye’s APY-9 radar, or as part of a follow-on sensor or platform,” Navair says in a statement.

After recently completing a contract to mature the UHF design while testing the multiband elements, North Star is now working on a $13.2 million contract to focus on refining the design of an integrated radar transceiver assembly.

At the core of the new technology is a second-generation UESA that has been in development for over 10 years.

The Navy experimented with UESA technology in the late 1990s and early 2000s for an E-2C radar modernization program that evolved into the E-2D configuration. But the Navy deemed the first-generation UESA radar too risky.

Instead, the Navy equipped the E-2D with the APY-9 radar, which includes the 7.3-m-dia. (24-ft.), 18-channel ADS-18 antenna with hybrid mechanical and electronic scanning.

The existing APY-9 operates the antenna in three modes within the UHF band: full mechanical scanning while turning at 6 rpm, a reduced rotation speed with electronic beam steering and a nonrotating radome with full electronic scanning in a 120-deg. section of airspace.

By comparison, the North Star radar would enable full electronic scanning across 360 deg. with twice the radiated power in two different bands of the spectrum. The North Star UESA is comprised of 54 transmit-receiver elements. The company is still deciding whether to feed the power through a 2:1 or 3:1 ratio coupler switch, allowing the radar to use either half or one-third of the elements at any one time. A 4,000-element S-band antenna also would be integrated within the circular array for dual-band coverage.