CW Power Capacity vs Frequency (Electromechanical Switches)

RF Electromechanical Relay Switches, RF electromechanical switches, or RF electromechanical relays are a type of RF switch with mechanical contacts driven by electrically driven actuators. The transmission paths within an Electromechanical relay switch are purely passive, and thus exhibit relatively low loss and high isolation compared to active switch technologies. Due to the low loss and low VSWR of this switch type, electromechanical relay switches are often used in test and measurement applications, or other applications where high power and fidelity are required.

The purpose of this switch type is to route RF signals, even to very high frequencies, to different paths and moderate switching speeds. There are a variety of different types of electromechanical relay switches, with a wide range of coaxial connectors, impedances, and complexity. The simplest of which is a single-pole-single-throw (SPST), but may have several poles and throws, such as a double-pole-double-throw (DPDT) or single-pole-twelve-throw (SP12T). Common coaxial connectors for these types of switches are SMA, BNC, and N, though there are many other connector types available.

Given the mechanical nature of the electromechanical relay switch contacts and electrical actuators, the performance of these switches is affected by a variety of factors. One of the main considerations is the continuous wave (CW) power handling capability of the switch as a function of frequency. It is important to note that the upper frequency limit of coaxial connectorized modules, including electromechanical relay switches, may be limited by the coaxial connector and not merely the internal transmission paths or other electronics or structures. Hence, for many electromechanical relay switches, the internal interconnect and contactor design is made so that the coaxial connector is the limiting factor.

Moreover, the coaxial connector type also has a maximum power handling capability based on the connector geometry and material construction. Typically, higher frequency capable coaxial connectors have lower power handling, as the frequency capability of a coaxial connector is dictated by the geometry and dielectric properties of the inner dielectric material. As RF losses are greater at higher frequencies, RF relays exhibit lower power handling at higher frequency regimes. This is often provided in the specification as a plot of power handling versus frequency (See Figure 1).

It can be observed from the plot of a DP3T Electromechanical Relay Latching Switch that the higher frequency capable switches (based on coaxial connector type) have lower power handling specifications. Also, at higher frequencies every electromechanical relay switch has lower power handling capability than at lower frequencies.