In the aerospace and defense sector, more opportunities are emerging for GaN-on-SiC MMIC PA solutions. Learn more about this technology and how it tackles modern challenges in the industry.
Elevating RF PA Performance in Aerospace and Defense
As our aerospace and defense systems become more advanced, they require better performance. This means it is imperative for Radio Frequency Power Amplifiers (RF PAs) to increase their performance to meet new expectations and solve challenges.
Read further to learn more about RF PAs and what the future holds for their development.
An RF PA is an electronic device used to increase the power of an RF signal. Developers of aerospace and defense systems need RF PAs to improve performance in applications such as military 5G and satellite communication. These systems must meet higher gain targets—but only if it won’t increase cost, complexity, size or weight.
Systems are beginning to use higher-order modulation schemes, which means they also must provide enough linearity and efficiency in environments more vulnerable to distortion than earlier schemes.
To solve these challenges, we look to a new generation of Gallium Nitride (GaN) Monolithic Microwave Integrated Circuits (MMIC) PAs.
New Applications, Tough Challenges
In the aerospace and defense market, there are many challenges and opportunities for RF PA technology in satellite communications, radar systems and upcoming 5G communications solutions for applications on and off the battlefield.
For instance, NASA has allowed private-sector companies to send off thousands of low-Earth-orbit (LEO) satellites. These circle the Earth and provide services such as broadband Internet access, navigation, maritime surveillance and remote sensing.
In military communications, RF PA technology can be used in numerous ways, ranging from satellite communication and tactical platforms and terminals to acoustical and optical communication platforms. Other applications include base communications infrastructure, network security and encryption systems and interception and jamming systems.
As an example, these radar systems can be used to alert pilots of any hostile or foreign radar activity and whether the radar interprets it as a friend or foe. Both primary and secondary radar systems are capable of this. A primary radar system broadcasts pulsed RF power and collects backscatter data that is used for tracking, surveillance and weather. A secondary radar system broadcasts RF signals at one frequency, which is received by an antenna and decoded, and responds on a different frequency. Besides performing friend-or-foe identification using 1030 Megahertz (MHz) and 1090 MHz frequencies, secondary radar systems double as distance-measuring equipment using the 960 MHz to 1090 MHz frequencies and can be used as general communications by means of transponders.
New mmWave 5G communications solutions will significantly improve the amount of information that can be shared for real-time decision-making and military applications due to their speed, ultra-wide bandwidth and low latency for broadband communication. RF PAs are needed to support these solutions. Previously, 5G systems operating in wide bandwidths were vulnerable to high-power jamming signals. Now, however, jammers will need to move into the mmWave range for these close-range 5G-based systems.
5G will enable a variety of different solutions. For example, it could be used in virtual reality solutions for remote vehicle operation in air, land and sea missions, as well as off the battlefield in smart warehouse, telemedicine and troop transportation applications. These applications all call for high-performance power technology to satisfy the high-speed data rates needed for video and broadband data.
RF PA Requirements Vary by Application
Aerospace and defense applications operate among different frequency bands. For example, satellite communications for LEO and geosynchronous communication operate in the K band (12 GHz to 40 GHz) while radar systems operate in the L band (1 GHz to 2 GHz). Selective response Mode S applications and weather radar systems operate under the S band (2 GHz to 4 GHz). The X band (8 GHz to 12 GHz) is intended for weather and aircraft radar, while the C band (4 GHz to 8 GHz) encompasses 5G and other sub-7 GHz communications applications. The highest bandwidths and data rates of these applications are provided by 5G mmWave, which runs in the 24 GHz+ frequency bands.
Every application has its own specific needs. For example, for 5G applications, an integral figure of merit is the PA’s linear output power. Power density must be as high as possible across a broad frequency range. A necessary PA trait is that it can operate in its linear region where distortion products are minimal. However, complexity, cost, size and weight will increase because more gain stages are required to offset the reduction in RF output power that can be delivered in this region. We also must consider gain AM/AM and AM/PM distortion—the output phase variation against input power often caused by a PA’s nonlinear capacitors.
There are also other types of distortion with satellite communications systems using higher-order modulation schemes, including 64/128/256 Quadrature Amplitude Modulation (QAM), which is particularly sensitive to non-linear behavior. Yet another challenge is reaching an acceptable peak-to-average power ratio (PAPR), which is the ratio of the highest power the PA produces to its average power. The PAPR is proportional to the average power and determines how much data can be sent. The size of the PA needed for a given format depends on the peak power. These challenges, among others, are only able to be resolved with GaN MMIC PAs, particularly for satellite and 5G applications.
GaN MMIC PA Benefits for Ka-Band Satcom Applications
The majority of modern LEO satellites operate in the 27.5 to 31 GHz Ka-band spectrum. Here, they are critical in supporting the mass amounts of traffic produced by video and other data-intensive applications. At these frequencies, traveling-wave tubes (TWTs) are traditionally used as power sources. However, GaN is more efficient and operates at lower voltages. GaN is also the best fit for any satellites in geosynchronous orbit that require inherent radiation tolerance. Additionally, GaN-based PAs are smaller than TWTs and more compatible with the requirements of active phased array antennas. They eliminate any need for complicated power combiners and deliver more RF power in a smaller footprint at higher voltages than gallium arsenide (GaAs).
GaN MMIC PA Benefits for Military 5G Networks
The mmWave (24 GHz to 100 GHz) frequency spectrum has less traffic than lower frequency bands that deal with TV, radio and 4G LTE networks operating between 800 and 3,000 MHz. More data can be carried at higher frequency bands, though over smaller areas. For the military’s next generation of close-range 5G-based systems, this is what they need. The mmWave band can increase bandwidth over networks that are smaller and densely populated both on and off the battlefield.
Thanks to GaN, 5G New Radio (NR) femto- and pico-cell base stations can extend deployments into the mmWave band for these military applications. Laterally-Diffused Metal-Oxide Semiconductor (LDMOS) metal-oxide-semiconductor field-effect transistor (MOSFETs) are not enough for greater than 3.5 GHz. Unlike GaAs, GaN offers the best mix of higher frequencies and power, wide bandwidth and the necessary thermal properties, gain, low latency and high switching speeds.
However, to fully reach their potential, GaN MMIC PAs also need silicon carbide (SiC) substrates. These enhance power density by allowing MMICs better thermal conductivity than that of silicon-based wafers.
Effects of Adding SiC Substrate
GaN MMIC PA power density can be improved with the use of SiC-based substrates, allowing superior thermal conductivity over what silicon-based wafers offer. Other advantages include higher wafer yields due to SiC having a better lattice match with GaN, a 20 percent smaller package size compared to LDMOS technology and more effectiveness. Systems for air and space use the most beneficial combination: high-power density and yield with the smallest footprint, less weight, maximum power support, greater efficiency and support for high-voltage operation with a longevity of at least 1 million hours at a junction temperature of 255°C.
Want More?
GaN MMIC PAs are becoming more prevalent in the market with more frequency options and choices of bare die and packaged MMIC PA products than ever before. For more information, visit our power device web page and check out our GaN-on-SiC products. Read more at Mobility Engineering.
Michael Ziehl and Baljit Chandhoke, Jul 30, 2024
Tags/Keywords: Aero-Defense, Communications
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