This article appeared in Microwaves & RF and has been published here with permission.
What you’ll learn:
- What role does an SPDT relay play in test applications?
- What are the benefits of a MEMS-based switch?
- Performance advantages over legacy technology.
Electromechanical relays (EMRs) are common workhorse components in the world of RF test and measurement systems. The single-pole/double-throw (SPDT) RF relay, for example, has been used for decades in a wide range of RF switching applications. In the parlance of relays and switches, “poles” (P) refer to the number of input ports on a relay while “throws” (T) convey the number of output ports.
An SPDT relay is a type of switch with one common input terminal and two output contacts, providing a straightforward way to switch between two circuits. An SPDT relay can perform a variety of functions in circuit and system designs. Depending on how a circuit is configured, the relay can serve as an on-off switch, a toggle between “ready” or “standby” modes, or to connect a common circuit to two separate paths in the circuit in which it’s operating.
RF Coaxial SPDT Relays
RF coaxial SPDT relays are standard components in signal-routing applications requiring a combination of high frequency, high power, and excellent RF performance. An RF coaxial SPDT relay, as its name implies, employs coaxial connectors and cables, and is designed to open and close circuit paths while introducing minimal RF mismatches, which can cause wave reflections.
RF coaxial SPDT relays can be used to route high-frequency RF signals from one transmission path to another. They’re frequently deployed in RF and microwave test systems to allow switching between two antenna signals or to route RF signals between different instruments, enabling multiple tests to be performed simultaneously utilizing the same setup.
Virtually all RF coaxial SPDT relays currently on the market are electromechanical switching devices rooted in 19th-century inventions by Thomas Edison and Joseph Henry. Even though EMRs remain ubiquitous in innumerable systems today, they’re technologically outdated. They’re bulky, slow, inefficient, unreliable, and expensive to manufacture at scale, and these major shortcomings can limit RF system performance, system reliability, insertion loss, and energy efficiency.
If that’s the case, then, why are RF coaxial SPDT EMRs still so widely used? Until now, there haven’t been many viable alternatives. The underlying electromechanical technology for RF coaxial switching and most relays hasn’t changed for decades.
A Different Approach with MEMS
A microelectromechanical (MEMS)-based switch addresses the fundamental shortcomings of EMRs and eliminates the compromises of legacy switches and relays. MEMS-based technology can effectively replace electromechanical switches and relays across many core applications, such as test and measurement equipment and RF and microwave systems.
MEMS switches and relays are smaller and lighter, consume very little power, switch at high speeds, have almost no insertion loss, and provide very high isolation. They also can operate well into the millimeter-wave (mmWave) spectrum while generating very little intermodulation distortion or harmonics. As MEMS devices, they can be provided in tiny packages that help shrink board size.
One example is Menlo Micro’s MM4002 RF coaxial SPDT relay (see figure). Designed to replace legacy electromechanical SPDT relays, the MM4002 is a miniaturized micromechanical coaxial SPDT relay based on the company’s “Ideal Switch” MEMS technology. Offering performance scaling from dc to 10 GHz, the MM4002 has a high-isolation, small-footprint relay that enables fast switching, low insertion loss, high input power handling, and reliable operation for over 3 billion switching cycles.
In comparison, conventional RF coaxial SPDT EMRs have limited lifetimes of less than 10 million cycles, becoming a potential point of failure in systems requiring high reliability. The MM4002 relay outperforms equivalent EMRs in all key figures of merit, providing a high-performance dc-to-10-GHz coaxial SPDT relay that offers lifetimes comparable to solid-state switches.
When a test-and-measurement system or 5G antenna design calls for an RF coaxial SPDT relay, consider the latest alternative to EMRs: smaller, faster, and more reliable MEMS-based switching technology. Consistent, reliable RF performance between switching cycles results in less downtime for recalibration of test systems, reducing long-term cost of test for RF applications. Making the switch from electromechanical to micromechanical technology may very well transform how you approach RF system design and test.