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Communications / SatCom

Modern Tactical Radio Needs GaN

Mar 05, 2021
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Tactical communication technologies have come a long way, from running cables in the field to maintaining situational awareness while conveying commands. In this age of network-centric conflict, IT infrastructure has travelled all the way to mobile command posts at the edge of the battlefield.

Military modernization continues relentlessly. An increase in military spending is driving procurement of advanced wireless communications systems across land, air, and maritime platforms. The global tactical communications market is set to grow at a compounded annual growth rate (CAGR) of 16% over the 2019-2025 period to reach US$18.53 billion.1

Increasing mobility, such as with small, lightweight military handheld radios, is a key growth trend in this market, and is challenging engineers with the critical requirements related to smaller size, lighter weight, and higher power.

Radio modernization

Radio technology continues to evolve to address communication challenges. For instance, UHF signals are attenuated by obstacles, such as walls and buildings, at the site of operations. Modern tactical radios overcome this challenge by using a multiple-in/multiple-out (MIMO) approach, splitting a single signal into several that occupy a higher bandwidth.

Yet another battlefield requirement pushes for higher bandwidth — the need to use broadband connections to send video, not just voice. Moreover, for several years, networked operations have demanded Software-Defined Radio (SDR) architectures that support multi-band and multi-standard operation.

This demands new specifications from the RF power amplifier, one of the core components in tactical radio equipment. The Joint Tactical Radio System (JTRS), for instance, requires that it cover VHF, UHF, and L-bands, while also delivering high efficiency, and small size and weight particularly for handheld radio equipment.

Key semiconductor technologies

Gallium Nitride helps reduce the size and weight of military radios while delivering the RF power needed for reliable communication.

GaN is a wide bandgap semiconductor. GaN’s bandgap of 3.4 eV against a technology like Si’s 1.1 eV means GaN has a much higher breakdown field of nearly 4 MV/cm compared with Si’s 0.2 MV/cm.2 This contributes to GaN’s high-temperature reliability and an exceptional power density capability that is typically five times higher than older technologies such as Silicon LDMOS (laterally diffused metal oxide semiconductor).3 GaN solutions therefore deliver the best size, weight and reliability for tactical radios.

Where older military radio systems had to use multiple devices to meet multiband design requirements, GaN enables video’s broadband and MIMO’s multiband transmissions with a single device. This translates directly to size, weight and system complexity reductions, and cost savings from a lower component count. There are still some radio systems that require separate solutions per frequency band, but GaN’s properties certainly allow it to be used across a wider band than other power amplifier technologies.

Mounted on another wide-bandgap material, silicon carbide (SiC), GaN delivers the highest possible performance that more than makes up for the lower cost of GaN on Si by utilizing SiC’s better thermal characteristics.

Designing with GaN

Wolfspeed’s CGHV27060MP 60 W high electron mobility transistor (HEMT) is such a high-performance GaN on SiC device. It is manufactured on the company’s 0.4 μm process for its 8 W/mm power density, >150 V breakdown, and 50 V operation for the highest power gain possible from a single-stage RF device.

It can be used in pulsed applications at UHF, L Band, or low S Band up to 2.7 GHz and is well suited for communication amplifiers with 10-15 W average power in high efficiency topologies like Class A/B, and F.

Figure 1: The CGHV27060MP-AMP3 test board comes with the GaN HEMT installed.
Figure 1: The CGHV27060MP-AMP3 test board comes with the GaN HEMT installed.

Engineers can evaluate the CGHV27060MP on the CGHV27060MP-AMP3 application fixture (figure 1). The class A/B circuit is specifically designed to address a wide 800 MHz-to-2.7 GHz operating frequency and 50 V operating voltage requirements.

In this circuit, the CGHV27060MP offers a gain G of 16.5 dB at VDD 50 V, IDQ 120 mA, and input power PIN 0 dBm. With PIN increased to 37 dBm, the output power POUT is 48.5 dBm and drain efficiency ƞ, 60%.

Wolfspeed has used its proprietary large signal transistor model for the CGHV27060MP as well as modeled all passive components in the design to include the effect of pad parasitics. This results in such tight alignment and high correlation between simulation and measurements, such as those for output power, drain efficiency, and gain (as shown in figure 2), that first pass success is achievable.

Figure 2: The CGHV27060MP-AMP3 performance at 37 dBm fixed input power from delivers over 48 dBm across the 800 MHz — 2,700 MHz band at saturated output power.
Figure 2: The CGHV27060MP-AMP3 performance at 37 dBm fixed input power from delivers over 48 dBm across the 800 MHz — 2,700 MHz band at saturated output power.

Meeting changing requirements

The tactical communications market exemplifies the Aerospace & Defense (A&D) notion of SWaP-C — the trade-off between size, weight, power and cost. Cost constraints often lead designers of handheld tactical radios and, sometimes, even manpack systems to seek components in low-cost plastic packaging.

While the solution above is offered in a ceramic package that can take on the thermal requirements of higher power systems, Wolfspeed understands the SWaP-C challenges and continues to innovate in this as well as many adjacent markets in the A∓D sector.

Visit Wolfspeed’s product page to learn how you can use CGHV27060MP and CGHV27060MP-AMP3 in your next tactical radio design.

References

  1. Tactical Communications Market: Global Trends, Market Share, Industry Size, Growth, Opportunities and Market Forecast — 2019 to 2025 (https://www.orionmarketreports.com/tactical-communications-2-market/26285/)
  2. GaN on SiC: The Substrate Challenge (https://www.wolfspeed.com/knowledge-center/article/gan-on-sic-the-substrate-challenge)
  3. LDMOS versus GaN RF Power Amplifier Comparison Based on the Computing Complexity Needed to Linearize the Output (https://www.mdpi.com/2079-9292/8/11/1260/htm)

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