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Fig. 1

Radar technology has been the backbone of the electronic military for many decades. Even as the technology continues to extend as the basis for numerous collision-avoidance systems in commercial automobile markets, it also expands into a growing number of military applications—specifically, as part of surveillance and tracking systems on the ground, at sea, in the air, and in outer space.

In the case of some airborne systems, such as in unmanned aerial vehicles (UAVs), an operator may be quite a distance from the radar system. In all cases, the feedback that these radar systems provide is invaluable.

Over the course of six decades, radar supplier Lockheed Martin has evolved its use of synthetic-aperture-radar (SAR) technology at lower frequencies, most recently expanding into highly efficient solid-state SAR systems. The firm’s solid-state ground-based surveillance and early-warning systems (Fig. 1) are capable of providing intelligence at any time.

These systems are neither limited by weather nor the atmospheric attenuation of conventional radars and electro-optical imaging systems. In addition to being used for moving target indication (MTI), the VHF/UHF SAR sensors have been used for ocean spill monitoring, polar ice assessment, intelligence acquisition, and battlefield reconnaissance.

Fig. 2

Military radar systems have traditionally been large electronic systems using vacuum-tube amplification to achieve megawatts of transmitted pulse-modulated output power at RF and microwave frequencies. The radar signal frequencies have always been dictated by the performance goals of a particular radar system. Lower frequencies and their longer wavelengths provide better surveillance of targets of interest at longer distances than higher-frequency signals and their shorter wavelengths, which offer more precise tracking at shorter distances.

A number of different signal-generation and -amplification electron-tube devices have been used in military radar systems, with magnetrons capable of producing output signals at megawatts of power and klystrons serving as effective amplifiers through kilowatts of output power. Traveling-wave tubes (TWTs) and TWT amplifiers (TWTAs) have also been utilized to amplify radar signals, as have crossed-field amplifiers (CFAs).

However, as has been true for frequencies from the audio range through microwave bands, designers have sought solid-state replacements for vacuum tubes. The basic tradeoff between the two technologies is that vacuum tubes provide enormous output-power levels compared to solid-state devices, but with much higher bias requirements and much shorter operating lifetimes. Thus, the key to using solid-state devices in applications such as radar systems that require high output signal levels is to combine the individual outputs of multiple transistors in parallel to achieve higher output-power levels.

Fig. 3

Gallium nitride (GaN) is a high-power semiconductor technology that has proven its worth in lower-microwave-frequency commercial applications such as Fourth-Generation (4G) wireless communications systems, and is gaining ground as an amplification solution for military radar systems. Earlier this year, one of the leaders in military radar technology, Raytheon Co., upgraded the main array of the Patriot Air and Missile Defense System with 360 deg. of coverage, along with GaN-based active electronically scanned array (AESA) technology.

“A GaN-based AESA radar benefits netted sensors, and gives Patriot greater capability and reliability while significantly reducing operations and sustainment cost,” explains Ralph Acaba, vice president of Integrated Air and Missile Defense at Raytheon’s Integrated Defense Systems business. “Raytheon recognizes how important this capability is for the warfighter, and is investing in its own resources to bring Patriot’s GaN-based AESA radar to the point where it can enter engineering and manufacturing development with low risk.”

The main AESA array measures about 13 × 9 ft. and is a bolt-on forward-facing replacement antenna. Earlier in the year, Raytheon built a GaN-based rear-panel array for the Patriot system (Fig. 2) as part of the efforts to enable a full 360-deg. view for the system. Raytheon also uses solid-state GaN technology for a U.S. Navy radar and jammer, and is exploring the use of the technology for the compact version of the Pentagon’s pain ray. Known as the Active Denial System, the pain ray uses a beam of RF/microwave energy to repel a living target by heating the skin.

Recently, Northrop Grumman Corp. received an award from the U.S. Marine Corps for nine AN/TPS-80 Ground/Air Task-Oriented Radar (GATOR) low-rate initial production (LRIP) systems (Fig. 3). The systems support air surveillance, weapon cueing, counter-fire target acquisition, and air-traffic control.

Northrop Grumman was previously contracted to supply six of the G/ATOR LRIP systems to the Marines, the first of which is scheduled for delivery by February 2017. By designing these latest nine systems around solid-state GaN technology for microwave amplification, the defense contractor has provided the Marine Corps with nearly $2 million in lifecycle cost savings per system.

“There are no other GaN ground-based AESA radars in production today,” says Roshan Roeder, director of mission solutions for Northrop Grumman. “G/ATOR is the first DoD ground-based AESA system to incorporate GaN in a production program. We proposed this technology as a cost-savings measure for the government and funded risk reduction internally to ensure a seamless insertion into the G/ATOR system. We are continuing to look at future technology insertions to continue providing the best capability out there to our warfighters at an affordable cost.”

GaN is a wide-bandgap semiconductor technology, with low parasitic capacitance and high breakdown voltage. It has wider bandgap than silicon-bipolar, silicon-carbide (SiC), and gallium-arsenide (GaAs) transistor technologies, and amplifier designers have succeeded in using GaN devices in high-efficiency Class E and Class F amplifier designs, with efficiency levels theoretically approaching 100%.

GaN material has excellent thermal-conductivity properties for low self-heating effects at high power levels. It also exhibits higher breakdown voltage, but lower carrier mobility, than GaAs, which will limit the upper frequency limits of GaN devices compared to GaAs transistors.

GaN-based power amplifiers for radar and other applications are available from a growing number of suppliers, including GaN-on-silicon-carbide (GaN-on-SiC) substrates for high-power amplifiers. For example, component supplier Aethercomm recently delivered an L-band amplifier with Class-F efficiency to a major defense contractor. The amplifier was based on off-the-shelf, packaged, GaN high-electron-mobility-transistor (HEMT) devices. The amplifier was capable of more than 50 W output power with efficiency of 60% or more.

The same company’s model SSPA 0.1-1.0-300 is a wideband amplifier that offers evidence of the capabilities of GaN technology. Designed for military and commercial applications, the GaN amplifier measures 5.25 × 10.15 × 1.97 in., weighs 8.5 lb., and is capable of 250 to 300 W average power from 10 to 1,000 MHz. It provides high efficiency and operates from a MIL-STD-461 aircraft power supply or an input voltage from +18 to +36 V dc.

In terms of radar market size, a number of market research forecasts agree that steady growth is expected for military radar markets around the world. British researcher Business Reports Updates  offers “Military Radar Systems Market Outlook 2016-2026,” a 329-page report that looks at 211 specific contracts by countries and breaks down markets into land-based, airborne, and maritime radar systems. It also provides profiles of the leading 13 military radar companies based on 2016 sales. The company also compiled the “Military Simulation, Modeling, and Virtual Training Market Report: 2016-2026,” a report on markets for military simulation.

According to a report from Market Research Media, “U.S. Military Unmanned Aerial Vehicles (UAV) Market Forecast 2013-2018,” the use of radar technology is expected to increase dramatically in UAVs for the next several years. UAVs equipped with low-power radar systems are viewed as attractive tools for performing remote surveillance.

The report projects the market for UAV radar systems to grow to $86.5 billion by 2018, rising at a compound annual growth rate (CAGR) of 12%. The use of solid-state GaN-based amplification can form the basis for lower-voltage radar systems that are practical, portable, and light in weight for realistic use in military and even government-sponsored UAVs, such as for weather radar UAVs.

In commercial markets, radar technology is being adopted widely in automotive safety systems for forward- and rear-looking, radar-based collision-avoidance systems. These are much higher-frequency radar emitters than in most military radar systems, operating at millimeter-wave frequencies up to 77 GHz and at frequencies well beyond the limits of GaN semiconductor technology—they typically use lower-power GaAs and silicon-germanium (SiGe) devices.

Whether for military, industrial, or commercial automotive applications, the spread of radar technology is almost relentless. Device technologies will continue to be developed or adapted to meet the different requirements.

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