RF Switch vs. RF Multiplexer: Key Differences Explained

This article compares RF switches and RF multiplexers, outlining their key differences based on various parameters.

RF Switch

An RF switch is a device that switches between different RF paths based on a specific switching configuration. It’s used for various applications including:

• Tx/Rx switching
• Automatic routing of RF signals
• Wireless test and measurement
• Turning RF signals ON and OFF

RF switches can be categorized into three main types:

• Electro-mechanical
• Solid state
• MEMS

Solid-state switches are further divided into PIN diode-based, FET-based, and hybrid types, depending on their operational principles.

Key specifications of RF switches include:

• Frequency range
• Characteristic impedance
• Insertion loss
• Return loss
• Isolation
• Switching speed
• Power handling capacity
• Rise time
• Dimensions and connectors

Architecturally, RF switches are either absorptive or reflective. Mechanically, they can be connectorized or drop-in types. RF switches with higher output modes, like 4x1 or 8x1, are often referred to as RF multiplexers. Conversely, switches with fewer output modes, such as SPST, SPDT, and SP3T, are commonly known as relays.

RF Multiplexer

An RF multiplexer is a device that combines multiple RF signals into a single port or separates a signal from one port into multiple signals on different ports or paths.

• When combining multiple signals into one output, it’s a multiplexer.
• When separating one signal input into multiple outputs, it’s a demultiplexer.

Common types of multiplexers include FDM (Frequency Division Multiplexing), TDM (Time Division Multiplexing), and CDM (Code Division Multiplexing).

Multiplexers increase the capacity of a channel to carry data. While similar to RF switches in routing RF signals, they typically use more ports. They allow multiple RF signals to be routed to a single port, based on the filters used in their design.

A 4-to-1 configuration is a common example of a multiplexer, specifically referred to as a quadplexer. Other variations include RF hexaplexers and RF pentaplexers.

For instance, the Keysight M9147A is an RF multiplexer that allows routing of a 3 GHz signal through any of the four RF switch multiplexers in a single PXI chassis module. Its specifications include:

• Configuration: 1 x 4
• Isolation: 50 dB at 1 GHz
• Insertion loss: 1.3 dB at 3 GHz

Conclusion

In summary, an RF switch is used to switch RF signals across different paths within a system. An RF multiplexer, on the other hand, combines multiple RF signals into a single RF signal or segregates one RF signal into multiple RF signals.