How RF resolves the life-or-death issue of SWaP

The Space Shuttle was once the main carrier for the U.S. space program—frankly, the global space exploration and satellite implementation program. The space shuttle (also known as the orbiter or O V) began design in 1969 and reached low Earth orbit in 1981. Specifically, special consideration is given to the power system (EPS). EPS includes power source reactant storage and distribution, fuel cell power plants (electricity generation), as well as power distribution and control. EPS provides 28 VDC and 115 VAC power rails for OV, spending a lot of time and effort on this. These systems and subsystems are very complex, cumbersome, and inefficient, but the power system is a crucial part of the entire payload calculation.

Flight history

Fast forward to 2015, several unmanned aerial vehicle projects were in development, and they belonged to a special category: High Altitude Long Endurance (HALE). One of the projects set a goal to fly for five years without refueling. The challenges of the environment, airframe, and power plant systems alone are daunting; moreover, focusing on electricity generation, transmission, and recycling is crucial to the success of such projects. In the design of communication systems, size, weight, and efficiency are also the most important considerations. Fortunately, Analog Devices, Inc. (adi) is very proactive in offering such devices.

A great example is ADI's transceiver series, which is diverse, covers the full spectrum, and features high integration, low power consumption, and compact size. A detailed discussion of these and other device solutions will be interspersed throughout this article.

Many of the issues and solutions in this article are illustrated using examples of aerial platforms, some of which are also applicable to marine platforms. Readers should understand that the statement of issues and related solutions for air-based and sea-based platforms is closely related and is often a different version of the same system.

What is SWaP BusinessPass?

It can be said that size, weight, and power consumption (SWaP) are the most important metrics in defining new products, projects, or platforms. Almost all newly developed tasks—whether sea, air, ground, portable, or held—share a common requirement: to do smaller, use fewer resources, and contribute more to overall system functionality. Recently, I spoke with a radar system architect about phased array radar and Active Electronically Scanned Array (AESA), which offer bird's-eye views from 50 to 1000 feet. The designers proposed some very clever ideas to improve system accuracy, range, and data transmission speed. However, SWaP demands rendered all his fine calculations useless. The current social, economic, political, and global environment favors thin and small systems. Over the years, SWaP seems to have become a key driving factor, forcing people to make some difficult trade-offs between system performance improvements and multifunctional architectures.

and uncovered the ringleader

Before discussing some solutions to SWaP issues, let's first look at a few of the "culprits" that triggered the problem.

Cu! copper is the preferred conductor for power transmission. A 1,000-foot uninsulated AWG No. 5 copper wire weighs nearly 100 pounds (50 kg). Worse still, the inherent resistance of copper wire causes some current to be wasted as heat. Another "bad guy" is the size of traditional devices. Taking marine radar local oscillator (LO) as an example, LO is fed simultaneously to both the transmitter and receiver. LO must produce stable frequencies with low harmonics, and the highest stability requirements must consider temperature, voltage, and mechanical drift. Oscillators must generate enough output power to effectively drive subsequent circuit stages, such as mixers or frequency multipliers. Its phase noise must be very low because signal timing is critical. Traditionally, LO is generated and distributed by independent, specially designed subsystems. The same applies to aerial systems, where solid-state component compositions result in large size, high power consumption, and bulky output.

The traditional device that provides high-power RF for systems is the traveling wave tube (TWT). So, since it's not broken yet, why repair Songtai? What is Songtai TWT? Songtai TWT is a specialized vacuum tube used in electronic devices to amplify microwave range radio frequency (RF) signals. Broadband TWT bandwidth can be up to one octave, but tuned (narrowband) versions are more common; The operating frequency range is from 300 MHz to 50 GHz. These TWT systems can be considered efficient, but they are single points of failure. Reliability is a serious issue for TWT. The reliability of microwave tubes mainly depends on three factors. First, defects introduced during manufacturing affect reliability. Production issues, poor workmanship, and lack of process control are the main causes of manufacturing defects. Second, the reliability of the traveling wave tube heavily depends on the operating program and handling. Finally, to ensure reliable operation, there must be a sufficiently large design margin between the operating point and the ultimate design capability of the tube. The above are just three examples among the many disadvantages of SWaP.

Save the superhero SWaP

Every villain needs a superhero to deal with. Advances in semiconductor technology and device integration have played a crucial role in reducing SWaP. Next, this article will introduce some major achievements that directly impact SWaP, making today's and foreseeable technological leaps possible. Below, three technologies are discussed: solid-state power amplifiers, device integration, and wireless sensor technology.

Solid-State Power Amplifiers (SSPA) are not a new technology. GaAs (gallium arsenide) and LDMOS (laterally diffused metal-oxide-semiconductor) have been used in high-power amplifiers for many years. Silicon-based LDMOS FETs are widely used in base station RF power amplifiers because they require high output power, and the corresponding drain-source breakdown voltage is usually above 60 V. Compared to other devices like GaAs FETs, their maximum power gain frequency is lower. LDMOS FETs are most efficient when operating below 5 GHz. A gallium arsenide field-effect transistor (GaAsFET) is a special type of FET used in microwave RF solid-state amplifier circuits. Its spectrum ranges from about 30 MHz to the millimeter wave band.

GaAsFETs are famous for their excellent sensitivity, especially the very low internal noise they generate. Power density is limited by breakdown voltage. In good weather, the breakdown voltage of GaAs MESFETs can reach 20 V. To recap, TWTs have high frequency and high power characteristics, but their reliability, weight, and required support subsystems make them unpopular. LDMOS can deliver high power but operates at frequencies below 5 GHz. GaAs MESFETs operate at very high frequencies, but their low breakdown voltage limits their power range to around 10 W. Where is the "hero"? Does Syntech have leapfrog SSPA technology to save the situation? BusinessTech SWaP prefers silicon carbide substrates with gallium nitride (SiC substrate GaN). Both GaN and SiC are wide bandgap materials, with combined breakdown voltages up to 150 V. This enables higher power density and lower line loads, making impedance matching easier. SiC substrate GaN supports millimeter-wave power gain frequencies (Ft ~ = 90 GHz, Fmax ~ 200 GHz).

The market acceptance of SiC substrate GaN LEDs has helped wafer fabs build confidence and reduce wafer costs. The device structure of RF transistors supports a power density of 5 W/mm. The MSL rating of SiC substrate GaN is close to or meets industry-recognized ratings. SiC substrate GaN has gained widespread recognition as a breakthrough technology, attracting a strong market attention. The biggest limitation on the performance of SiC substrate GaN is heat transfer, and diverting heat from the device is the final issue to be solved. There has been some success with silicon substrate GaN, but the lower thermal conductivity limits output power to around 10 W. Diamond substrates with GaN performance are the best. The power density calculated by scientific calculations is ten times higher than that of currently available SiC substrates in GaN.

Although direct GaN growth on single-crystal diamonds has been demonstrated, the maximum size of currently available monocrystalline diamond substrates limits the adoption of this technology. Governments and defense contractors are the only early adopters of diamond substrate GaN. Similar to GaAs in the 1980s, diamond substrate GaN will be reviewed by these government agencies, and as reliability improves and related costs decrease, the commercial market will follow. TWT has an integrated SSPA alternative. ADI offers a high-power amplifier (HPA) with up to 8 kW, which integrates many SiC substrates of GaN SSPA into a single unit. The KHPA-0811 uses a compact dodecahedral package, designed to balance high power and small size while covering wide bandwidth.

Eliminating useless 'anchors' through integration

The term "ship anchor" here is a term used by the U.S. Navy. When a large electronic (or other) device becomes outdated and becomes a burden on system resources, it is called a "ship anchor." Whether manned or autonomous, airborne platforms have many forms of airborne communication. Voice, navigation, data, onboard sensors, radar, and more all have their own communication links. As the sky becomes more crowded, the list of links grows longer. In the past, any system required a considerable amount of area, power, and support subsystems. It's truly remarkable that the aerial platform can take off. Every ounce and every watt consumed must be carefully calculated, and the physical system design must match the space allocated to it. There must be a better way.

The AD9361 is a high-performance, highly integrated RF Agile Transceiver transceiver™. The AD9671 is also from ADI, featuring low cost, low power consumption, and compact size. Advances in integrated circuit (IC) design, system-in-package (SiP), and system-on-chip (SoC) have rendered these bulky systems as "anchors" a thing of the past. Let's look at a good example of system integration. ADI has released an industry-leading transceiver that integrates a large number of high-power communication links into a single 10 mm × 10 mm package. The original design was originally intended for 8-channel ultrasound solutions, but many system designers wanted to use COTS devices because of their high integration, low cost, and easy availability. Ultra-wideband, low-power, low-cost transceivers ADF7242 another example of integrated design, and systems outside the original design scope are also considering using it. Dropping the "anchor" and using SiP and SoC.

Cutting off the copper 'umbilical cord'

Whether manned or unmanned, aircraft have hundreds or thousands of sensors, many with redundancy and backup support systems. There is a wide variety of sensors, including flap and aileron position sensors, engine vibration sensors, brake temperature sensors, and more, and the number is continuously increasing. Each sensor and its associated redundancies are connected to the CPU via large, heavy copper cables and stainless steel/aluminum connectors. The problem is that a considerable amount of platform resources is used to support these cables and interconnects. Advances in RF technology can also save SWaP by reducing dependence on such cables. Many major airframe manufacturers are collaborating to certify commercial finished product (COTS) technologies in order to replace copper interconnects with low-cost, reliable methods.

The ADuCRF101 is a fully integrated data acquisition solution designed for low-power wireless applications. For example, it uses an inertial measurement unit (IMU) sensor with output data bandwidth requirements below several tens of kHz, combined with ADI's integrated RF transceiver precision analog microcontroller ARm® Cortex-M3®. Its design emphasizes flexibility, stability, ease of use, and low power consumption. This combination is purely hypothetical, but it could be an example of avionics sensor technology being used in conjunction with COTS RF devices. It is believed that such RF solutions will soon be used to save SWaP.

Conclusion

Today's social, political, and economic environment demands that aerial platform designers focus more on saving size, weight, and power consumption. Reducing system resource burdens can extend voyage times, lower fuel requirements, and improve payload efficiency. The most important and interesting progress in saving SWaP comes directly from technological advances in the RF field. The most favorable progress is due to the reduction in size, device integration, and reduced reliance on copper cable interconnects brought by the shift from TWT to SSPA. RF technology is expected to keep the aviation industry soaring for many years to come. RF solutions play an indispensable role in reducing SWaP.