RF and microwave suppliers for military use face demands for innovation

Story

January 15, 2020

The U.S. military is quickly realizing that modernization
efforts for RF [radio frequency] and microwave components are necessary in
order to keep pace with advancing adversaries, and major component suppliers
are ready for the challenge.

Even at its stealthiest moments, war is loud. Not always in
the vein of cacophonous, artillery-heavy combat, but think instead of the constant
radio-frequency (RF) and microwave communications warfighters and their
electronic warfare (EW) solutions emit. Size, weight, and power (SWaP)
limitations; the introduction of GaN [gallium nitride]; and the need for wider
bandwidths have all driven the demand for specific RF and microwave
capabilities. To better understand the engineering challenges manufacturers
face, let’s examine the fact that while RF and microwave components do have
similarities, radar and EW requirements differ in a significant way.

At a surface level, radar is primarily used in intelligence,
surveillance, and reconnaissance (ISR) settings as well as in communications.
In these instances, the radar is highly pulsed; quick transmission and
efficient analysis of the data received prevents adversaries from locating
positions. As a result, radar’s existence on the electromagnetic spectrum (EM) is
far more limited than most EW solutions.

Jamming, intercepting, and counterattacks are a few of the
capabilities expected of EW but not always of pure radar. These capabilities
require low latency to reduce the time between when a signal hits, when it’s
converted in a processor, and is then sent back out – all areas in which
adversaries have made recognized strides, according to industry professionals.
Thermal management is also crucial for EW, since EW transmits continuous waves rather
than the pulsed RF of radar.

These operational differences provide warfighters with
electronic reinforcement on the battlefield, but also create incredibly
specific and challenging design requirements for suppliers. SWaP innovations
have already begun to change the military RF and microwave game in notable ways
and will arguably act as the first step toward the complete modernization of EW
components, according to leading industry suppliers.

SWaP’s persistent influence

With reduced SWaP limitations remaining a constant factor in
the design of military capabilities spanning beyond just RF and microwave
components, engineers have been tasked with designing innovative ways to
shrink, cool, and speed up EW operating systems. One method that has gained
traction in the industry has been die-level packaging.

“With certain reduction of size and weight, a lot of that
comes down to how we package these devices,” says Dean White, senior director
for HPS market strategy high performance solutions at Qorvo (Greensboro, North
Carolina). “We’re always looking for ways to take the device and put it into a package
that is just a little bit bigger than the die itself. There’s a lot of
different trends in terms of packaging, even down to the point of doing
wafer-level packaging.”

The question has now become: Does the U.S. have the packaging
know-how to integrate revolutionary new technologies? The Department of Defense
(DoD) and the U.S. Navy, needing an answer to just this question, established
the State-of-the-art Heterogenous Integrated Packaging (SHIP) prototype
project, of which Qorvo is an awardee.

The motivation behind the program is onshore, SWaP-defined
integration intended to lower supply-chain risk and protect the DoD’s
intellectual property, all while achieving lower power consumption, reducing
physical size, and improving performance.

Regardless of participation in the SHIP project,
microelectronics companies seem to agree that integration will play a key role
in overcoming SWaP challenges in military RF and microwave technology.

“We have developed multiple strategies to reduce SWaP requirements
of our RF and microwave products,” says Mario LaMarche, senior product
marketing manager for RF, microwave, and mixed-signal product lines at Mercury
Systems (Andover, Massachusetts). “Two that I’ll highlight are utilizing
advanced modeling in the design phase, and RF and digital integration. Through
accurate nonlinear models we are able to significantly increase the circuit
density while minimizing the performance effects.” (Figure 1.)

Figure 1 | The Mercury Systems RFM3101 compact 3U OpenVPX transceiver – operating from 6 GHz to 18 GHz – is designed to support demanding EW applications.

Mastering the packaging side gives companies a notable
advantage in the industry. However, while having the skill set to manufacture
these smaller and smaller form factors is important, making use of resources
like foundries and semiconductor fabrication plants (fabs) can make all the
difference.

The role of foundries and fabs

Fabs are where microelectronics, such as the chips and wafers
used in RF and microwave capabilities, are manufactured and then sold to
third-party companies that aren’t equipped with the foundry to build it
themselves. When attempting to achieve the most cost-efficient, customizable, SWaP-optimized
product for the customer, this can present itself as a challenge for the
company.

“Having the ability to actually make, manufacture, and have
all of those components is pretty key,” says Sean D’Arcy, director of aerospace
and defense at Analog Devices (Norwood, Massachusetts). “That’s the kind of
solution you’re going to have to have to be able to get there. It’s putting a
lot of pressure on some of the larger guys who don’t have a foundry or fab and
those core products because they’re buying them.”

With vertical integration becoming a prominent trend in the
industry, the existence of a company-owned fab can be the final arbiter in
whether or not a specific design can be engineered (Figure 2). Integration
means that these companies are either custom making monolithic solutions or
taking dies and putting them on a package with complex interposes.

Figure 2 | The Analog Devices ADAR1000 is a four-channel, X- and Ku-frequency band, beamforming core chip for phased arrays with both an integrated temperature sensor and an 8-bit ADC.

According to industry professionals, the benefits that a fab
provides are almost the only way a microelectronics company can keep up with
the cutting-edge design trends in military RF and microwave electronics.

“The primes are looking inward again,” says Damian McCann,
associate director of development engineering at Microchip (Chandler, Arizona).
“What we’re seeing is a push for the primes to reestablish their internal
capability.”

Fabs and foundries contribute to the ever-present goal of cutting
costs and increasing efficiency that define much of the radar and EW market,
and so does the use of new materials, like GaN. It has been a revolutionary
addition to the industry, pushing RF and microwave electronics one step closer
to achieving higher voltage and more proficient power dissipation.

GaN continues to impress

Transformation within the military RF and microwave market
has resulted in the introduction of several new, cost-efficient, and more
easily packaged materials. Silicon carbide (SiC), laterally diffused
metal-oxide semiconductors (LDMOS), and GaN are three of the top players that
manufacturers seem to be reaching for when the goal is to enable higher
voltages in an all-around more affordable product.

As a leader in LDMOS technology, NXP has seen firsthand the
industry’s gradual lean toward to the use of GaN in RF power solutions.
According to company officials, the military is adamantly pushing for GaN because
of its attractive price point. However, this doesn’t mean that the materials
can’t work together in powering critical RF solutions.

Figure 3 | NXP’s MMRF5021HS uses 50 V GaN and is designed for wideband applications.

“In the past, we used to call it LDMOS versus GaN, now we
call it LDMOS and GaN because they can be
complimentary.” Says Gavin Smith, RF product marketing manager at NXP (Chandler,
Arizona). “We can use LDMOS in certain ranges, and GaN in others. Maybe
potentially using LDMOS as a driver with GaN.”

Internal research and development for phased array, specifically
analog phased array, have also benefited from the use of GaN. As the accepted
design implementation that’s been in favor for years gets shrunk down and
pushed higher in the spectrum, power levels need to be managed accordingly.
That’s where GaN comes into play.

“GaN technology is what enables the next generation, so you
will see a lot of that. As far as its ability to put out a significant amount
of power, less of the energy is converted to heat.” D’Arcy says. “But you always
have to think about what is beyond GaN. Our industry tends to get a little
caught up on the process or the material, but if you think about our end
customer, they don’t care if it’s made of diamond as long as it works.”

Military RF and microwave customers may have their specific
customizations, cost parameters, and radar/EW needs, but warfighters are just
as eager to start using the next best thing as the engineers are to fabricate
them. The DoD just needs to back it first.

Advancements drive military funding

Military funding has been heavily influenced by the military regaining
the advantage in the U.S. and with NATO allies and could mean a climb up in the
EM spectrum.

A general push toward higher frequencies and voltages has
influenced the direction of military spending, as these require reliable power
dissipation, efficient thermal management, and creative methods of integration.

“Our adversaries are becoming increasingly more complex, and
RF and microwave is where we need to be advancing the fastest,” D’Arcy says. “Another
factor that drives military funding, whether this be perception or reality, is
spectral dominance where we need to not just be able to jam and protect, but we
also need to be able to function and have our GPS and our systems work as well,
and a lot of that is RF and microwave.”

Small-swarm unmanned aerial vehicles (UAVs) also present
another radar challenge that has influenced funding, along with ships and
sea-skimming missiles on the naval side. Adversaries are getting better at
hiding in the noise, but the U.S. is experimenting with ways to get better at
finding them.

Some other up-and-coming concepts floating around the
military RF and microwave industry include radar-guided rounds and kinetic
weapons. What kinds of accommodations these will need is not yet clear, but
they are enticing to the DoD, and these new potential technologies are driving
change and spending for research and development.

Figure 4 | Qorvo’s QPA2212 is a KA-band power amplifier, ideally suited to applications ranging from satellite communications to 5G infrastructure.

“If you put enough hours and money behind it, you come up
with these fantastic results,” Qorvo’s White says. “The military just continues
to challenge us. They’re always asking us to be a little better than we were
last year.” (Figure 4.)