Next-Gen RF Communications Breaking the SWaP Bottleneck with Ideal Switch Technology

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Menlo Microsystems, Inc. ​ Chris Keimel CTO

GGB Heilbronn GmbH

Ensuring robust, high-quality, mission-critical communications in the adverse environment of space places extremely demanding requirements on satellite system designers. Each gram of mass, milliwatt of energy consumption and cubic centimeter of occupied volume are scrutinized right down to the size, weight, and power (SWaP) implications of each constituent component.

The SWaP specifications of multitude of embedded switches have a fundamental impact on the operation of the beamformers and a significant influence on the overall performance of the satellite. The physical space occupied by switches affects the dimensions of the sub-system, their aggregated mass has launch and operational considerations, the electric power consumption places demand on the solar arrays and the heat generated needs to be managed and dissipated in an appropriate way.

Legacy systems and their limitations

Component life expectancy is of primary importance in a situation where failure could be fatal for the host device and issue resolution options are limited. Accordingly, a preference had emerged for solid state switches, capable of billions of operations. However, with insertion losses of up to 6 dB, significant passive power consumption, and maximum power handling capabilities of around 5 W, solid-state switches are not without their limitations. They dissipate significant heat waste, which requires substantial thermal management solutions such as large heat sinks to remain operational. The bulky, heavy, and power-hungry nature of solid-state switches is therefore impeding the development of mission-critical communications and limiting more rapid adoption of processor-hungry technologies such as AI that are capable of bringing more autonomy to space missions.

The role of RF switch technology

On satellites, switches fulfill the role of routing signals in the payload and control the operation of attenuators and phase shifters that feed phased-array antennas to manage the beamforming. Agile, efficient, and effective beamforming is critical to ensuring availability and quality-of-service of the communications link. However, system designers need to reconcile these requirements without burdening the satellite or tactical radio with an impractical demand for size, weight, and power.

Historically, system engineers have had to make difficult switch selection decisions, trading off specifications between electromechanical relays (EMRs) and solid-state switches, then taking the compromises associated with those choices. EMRs offer lower insertion loss over a broad spectrum with higher power handling but with limitations in size, weight, life expectancy, and speed. Whereas solid state switches are significantly faster, smaller, and have near infinite life with tradeoffs in insertion loss, spectral coverage, power handling and thermal management. Semiconductors, as the name implies, are inherently lossy and that impacts the efficiency and energy budget of the host device, consuming power and generating heat, even when in the off state. The compromises inherent in these traditional switch options create a bottleneck restricting the migration to faster data rate and higher quality-of-service applications.

The Ideal Switch concept – A technology shift

Significant research has been conducted in recent years to develop a new category of switch based on Micro-Electro-Mechanical Systems (MEMS), developed to address and resolve design compromises related to size, weight, power, frequency coverage, life expectancy and linearity all within a single chip technology. What has emerged is a MEMS switch with true DC to mmWave coverage with superior performance in a small chip-scale package. Based on proprietary manufacturing processes and innovative materials science originally developed at General Electric (GE), Menlo Microsystems is further advancing and commercializing the technology as the Ideal Switch.

Combining semiconductor manufacturing techniques with a robust metallic micro-mechanical actuator, this new category of RF switch achieves microsecond switching speeds, stable ohmic performance over cycles, temperature insensitivity, along with air gap lever leakage and isolation. It consists of three fundamental parts: a durable beam made of proprietary alloys, a low resistance ohmic metal contact, and an ultra-low power consumption electrostatic gate. It has universal signal coverage, able to carry AC/DC and RF signals with linear performance from DC to > 50 GHz. The miniaturized, paired-back design utilizing innovative materials means it is extremely fast and durable, switching at <10μs, with a life expectancy in excess of three billion operations.

Impact on system-level design

When we examine the impact of adopting MEMS switches for mission-critical communications, we can see clear advantages. For example, a beamformer typically consumes up to 25% of a satellite’s energy budget. If you replace the beamformer’s solid-state switches with MEMS switches and take advantage of the favorable power consumption and insertion loss, the power budget can be reduced to less than 5% without compromising reliability in a form factor reduced by around 60%. Furthermore, the frequency range over which the switch can achieve low insertion loss is something solid-state switches cannot compete with, offering less than 1 dB of insertion loss from DC to 50 gigahertz in a single component. For passive components in particular, it forces a rethink of the traditional multi-band approach to payload design towards a unified ultra-broadband system.

The small form-factor, fast switching speed and high power handling over a very broad frequency range, represents a near-universal component, able to address a wide range of applications. With due consideration to the capabilities of the other payload components, this opens the possibility to transition from dedicated, single-mission platforms to more agile, reconfigurable, multi-mission platforms. Either in a primary role as an upgradable communications satellite or serving as an in-orbit servicing platform (IOSP), able to inspect, repair, refuel, upgrade, or extend the life of other satellites while in orbit.

Linearity issues in the RF domain, even for passive components, degrade the spectral purity and give rise to unintentional modulation. This translates to incorrect functioning of the beamformer (beam squint) as well as a reduction in modulation quality and subsequent errors in the digital domain. Because the linearity of these new MEMS switches (IP3 > 90 dBm) can be several orders of magnitude superior to typical solid-state switches, the system can operate at higher powers without significant distortion, thus improving energy efficiency and the quality of the service delivered to end users.

Furthermore, the temperature range of this new category of switch is remarkable when compared with solid-state switches. With a near-zero temperature coefficient, these ohmic switches maintain consistent s-parameter performance throughout an operating temperature of -40 to 150 °C. They have even demonstrated consistent performance when tested to millikelvin temperatures. In effect, this minimizes an onerous satellite design consideration where thermal effects are particularly problematic.

The contribution of this category of switch to satellite design should not be considered in isolation, there are indirect implications which become apparent when integrating this new type of MEMS component. Lowering the power consumption of the switch impacts the entire RF power budget of the system or sub-system, meaning that designers can relax the requirements for other components, for example backing off the operation point of amplifiers and further decreasing power DC consumption and thereby significantly improving signal quality.

Outlook and industry implications

Space and military (MIL) grade components must meet extremely stringent reliability and environmental requirements. With this latest switch technology guaranteed for 3 billion cycles and with typical operation achieving more than 10 billion cycles, MEMS switches can meet the cycle life required for mission-critical communication systems. Designers can utilize the low overhead, easy integration capability of MEMS switches to upgrade existing satellite platforms and can address more ambitious applications such as digital beamforming and larger constellation, multi-mission communications systems.

Conclusion

As mission-critical communications develop to deliver new services which require higher frequency bands, wider bandwidths, more power, and demanding quality of service, against an overall trend towards miniaturization, we start to approach the limits of what can be fulfilled using traditional switch technologies. MEMS switches offer significant size, weight and power benefits and the possibility to significantly mitigate design compromises for applications ranging from satellite communications, and missile guidance to intelligence, surveillance, and reconnaissance. The adoption of this technology creates new possibilities for current and next-generation mission-critical satellite communications and because switches are the most fundamental building blocks in electronics, controlling the operation of every device you can imagine, the potential impact is extremely wide-ranging. (mr)