Switches
6 subcategories
Test switches are fundamental components in automated test systems, routing signals between instruments and devices under test (DUT) to maximize channel efficiency and eliminate manual cable swapping. Selecting the correct switch configuration depends heavily on the operating frequency range, impedance matching, power handling, and mechanical longevity required by the application. Coaxial switches route high-frequency microwave and RF signals, offering frequency capabilities from DC up to 67 GHz. In contrast, general-purpose switch modules focus on low-frequency control, DC power routing, and actuator logic. When integrating switches into large automated setups, system designers must choose between individual electromechanical relays, multi-channel modular cards housed in dedicated control mainframes, and external driver units that supply the necessary actuation current. This guide reviews the core parameters of test switches, outlining how configuration, termination, and control architectures influence system performance.
- Maximum Coaxial Frequency
- 67 GHz
- RF Repeatability
- 0.03 dB maximum
- Typical Actuator Speed
- < 15 ms
- Minimum Switch Cycle Life
- 5,000,000 cycles
Subcategories
Switch Configurations and Terminations
Coaxial signal routing utilizes specific multi-port architectures depending on the number of active signal paths required. Single-pole double-throw (SPDT) switches, such as the Keysight Technologies (Agilent HP) N1810TL, Keysight Technologies (Agilent HP) 8762B, and Keysight Technologies (Agilent HP) N1810UL, route a single input to one of two paths. For complex multi-port setups, designers use multiport configurations, including SP3T designs like the Keysight Technologies (Agilent HP) 8766K, SP4T designs like the Keysight Technologies (Agilent HP) 87104B and Keysight Technologies (Agilent HP) 87104C, and SP6T options like the Keysight Technologies (Agilent HP) 87106B.
A key electrical consideration is whether to choose a terminated or unterminated configuration. Terminated switches automatically connect unused ports to an internal 50 Ω load. This is a critical feature of the Keysight Technologies (Agilent HP) 87104C and Keysight Technologies (Agilent HP) 8762B, helping protect upstream components from reflective signals and maintaining proper system impedance. Unterminated models, such as the Keysight Technologies (Agilent HP) N1810UL, leave unused ports open-circuited, which is acceptable in systems where reflections do not degrade measurement performance.
General Purpose and Low Frequency Routing
When routing DC signals, low-frequency AC, or power lines, high-frequency coaxial designs are replaced by general-purpose switch cards and actuator modules. The Keysight Technologies (Agilent HP) 34903A is a 20-channel general-purpose actuator module containing independent SPDT latching relays. It operates up to 300 V and 1 A, with a 10 MHz typical bandwidth, making it ideal for system control and power switching.
To manage multiple switch cards in a single system, programmable switch/control mainframes are deployed. The Keysight Technologies (Agilent HP) 3488A provides five module slots supporting up to 50 channels of low-frequency signal routing. It features local display feedback, state storage memory, and GPIB (IEEE-488.1) interfaces for integration into larger automated setups.
Actuation and Switch Drivers
Electromechanical coaxial switches use physical contacts driven by magnetic solenoid coils. Latching actuators are preferred for high-frequency testing because they require actuation current only during the short transition phase (under 15 ms for the Keysight Technologies (Agilent HP) 87104C and Keysight Technologies (Agilent HP) 87106B). Once switched, they draw 0 mA of continuous holding current, minimizing heat dissipation and thermal offset.
Driving these electromechanical relays requires specialized controller electronics. The Keysight Technologies (Agilent HP) 11713A is an external attenuator and switch driver that supplies a +24 Vdc common drive voltage across 10 independent current-sinking contacts. It provides the front-panel manual control and remote GPIB interface necessary to actuate individual relays or step attenuators reliably without overloading system controller resources.
Frequently asked questions
- What is insertion loss repeatability and why is it important?
- Insertion loss repeatability represents the variance in signal attenuation each time the switch returns to a specific state. For high-precision RF test setups, models like the Keysight Technologies (Agilent HP) N1810TL and 87104C offer a repeatability of 0.03 dB maximum over 5 million cycles, ensuring measurement calibration remains stable.
- What are the benefits of using a terminated coaxial switch?
- Terminated coaxial switches, such as the Keysight Technologies (Agilent HP) 87106B, shunt unused ports to an internal 50 Ω resistor (typically rated for 1 W continuous RF power). This prevents open-circuit reflections from traveling back into the signal path, which helps preserve the voltage standing wave ratio (VSWR) and signal integrity.
- How are multiple coaxial switches driven from a single controller?
- A dedicated switch driver like the Keysight Technologies (Agilent HP) 11713A can be used. It provides up to 10 drive channels sinking +24 Vdc, allowing it to control multiple electromechanical switches or programmable step attenuators concurrently via GPIB commands or front panel input.