The defense sector continues to grow, with various countries increasing their defense budgets and contributing to between 3% and 4% growth in 2020 to reach $1.9 trillion in total, according to consultancy Deloitte.[1]
A key piece of equipment for not only the defense market but for commercial navigation as well is X-band (8 GHz to 12 GHz) radar. While aviation is one of the major industries extensively using them, X-band radars are now being deployed across a wide range of applications, including fire-control systems and other military platforms, unmanned aerial vehicles, maritime vessel traffic control, weather monitoring, bird activity detection near airports, and anti-icing remote sensing.
According to market researcher Strategy Analytics, it is the largest radar segment, with sales in this band reaching nearly $6.3 billion in 2018 and expenditures set to grow at an estimated compound annual growth rate of 3.4% to cross $8.7 billion in 2028.[2]
But it isn’t just any X-band radar that represents a significant growth opportunity. Increasingly, the development focus is on active electronically scanned array (AESA) systems, primarily for large airborne platforms, followed by land and marine segments, respectively.
The AESA Challenge
AESA systems use active arrays, each with hundreds or even thousands of antennas. Each antenna has its own phase and gain control. The interference or superposition of individual wavefronts from the antenna elements is used to create a plane wave, effectively generating a beam of radio waves traveling in a specific direction. By shifting the phase of the antenna elements, AESA radar systems electronically steer the beams.
The antenna elements are typically spaced at half-wavelength to decrease exposure in the near field. AESA radars are also often required to spread their signals across a wide range of high frequencies. This frequency agility allows them to quickly search across a sector for targets. It also makes them more difficult to detect over background noise. This allows ships and aircraft to radiate powerful radar signals while remaining stealthy and more resistant to jamming.
These requirements present engineers with several challenges: Each antenna element must be small and light enough to allow fractional wavelength spacing as well as keep the overall system size and weight manageable for airborne and marine use. Yet, depending on the application, the radar system must be powerful enough to output anywhere from several hundred watts to a high 100 kW, which, in turn, would require effective cooling, thus increasing size and weight.
As in many such use cases, the system is evaluated on the basis of size, weight, power, and cost (SWaP-C). Replacing just a few components in the system does not make much of a dent in those considerations. The technology enabling AESA radar systems must therefore offer significant benefits in terms of SWaP-C improvements.
Enabling Technology: GaN
The technology that helps radar designers overcome challenges of power, cooling, weight, and size with cost-effectiveness is gallium nitride (GaN). The material’s high electron mobility, and GaN-based devices’ low gate charge as well as low output capacitance compared with silicon, provide higher gain at higher frequencies with better efficiency.
GaN’s wide bandgap and extremely high critical electric field for breakdown results in high-temperature reliability, ruggedness at high supply voltages, and exceptional power density.
On a silicon carbide (SiC) substrate, which offers low thermal expansion, low lattice mismatch, and exceptional thermal conductivity, GaN’s characteristics are best utilized. The thermal conductivity of SiC is 430 W/mK for the 4H-semi-insulating polytype against silicon’s low 146 W/mK. This allows very high power densities to be achieved, with heat efficiently dissipated to prevent reaching extreme channel temperatures that would otherwise destroy device operation.
GaN on SiC amplifiers in AESA radars therefore make it possible to achieve higher performance, delivering equivalent output power with smaller form factors and requiring less cooling. But more is needed in terms of device technology to significantly boost SWaP-C improvements.
Package is Key
Further advancement of phased arrays, such as AESA radar systems, requires reduction in size as well as a tighter integration of components.
Monolithic microwave integrated circuits (MMICs) are one such technology that increases circuit density by fabricating entire functional blocks of several components on a single device. MMICs offer additional benefits of minimizing component mismatches, decreasing signal delay due to shorter distances between the components on a MMIC, and reducing overall BoM costs.
Packaging MMICs in quad flat no-lead (QFN) packages provides the further advantages of low cost and smaller form factor. QFN packages also help decrease lead inductance because they use short bond wires, and their exposed copper die pad enables excellent thermal performance.
Wolfspeed’s CMPA901A020S comes in such a 6 × 6-mm QFN package — a 20-W GaN on SiC high-power amplifier operating from 9 GHz to 10 GHz for pulsed radar applications such as marine weather radar. With three stages of gain, the amplifier provides >30 dB of large signal gain and >50% efficiency to support lower system DC power requirements and simpler system thermal management solutions.
CMPA9396025S is another GaN MMIC that exemplifies a union of technologies to maximize SWaP-C improvements. Designed for 9.3-GHz to 9.6-GHz operation, this three-stage device delivers 25 W at 100-s pulse width and 10% duty cycle from a 6 × 6-mm QFN package.
Wider band and higher power operation in the X-band is enabled by the CMPA801B030 family of MMIC amplifiers that operate over the 7.9-GHz to 11-GHz frequency range. It outputs an incredible 40 W typical with >20 dB of large-signal gain and 40% power-added efficiency. The product family is offered in a 7 × 7-mm plastic overmold QFN, as a bare die, as well in a 10-lead metal/ceramic flanged package for higher electrical and thermal performance.
Enabling Radar Evolution
Strategy Analytics believes that such GaN devices as those described above will help drive fast adoption of AESA radar across a growing variety of platforms, with GaN expenditures for radar systems in particular being well poised to skyrocket from $171.8 million in 2018 to $734.1 million in 2028.
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