RF Switch Testing: Decoding the Secrets in High-Speed Streaming

In modern RF front-end modules, components such as power amplifiers (PAs), low-noise amplifiers (LNAs), multiplexers, transceiver switches and antenna switches play a key role. Among them, the role of RF switches cannot be ignored, which are responsible for realizing directional propagation between transceiver and antenna signals, coupling transmitter signals to the antenna or antenna signals to the receiver, and isolating the transmitter signals from the receiver to avoid the receiver link being interfered by the transmitter. Today, we will explore the importance of RF switches in test and measurement applications.

(I) Basic Information

In communication, sensing and test and measurement applications, RF switches are basic components in RF circuits. RF switches are typically used to switch between receive or transmit channels at antenna ports, to switch between filter channels, or in matrices to switch test channels for high-throughput automated testing or to expand the number of ports in a vector network analyzer.

The RF switch may be integrated in an RF semiconductor device, as solid-state switches, discrete solid-state switches, or microelectromechanical (MEMS) switches may be relatively large connectorized components that rely on embedded motors to engage different paths of the switching mechanism.

The RF switches may have a pair of multiple paths in which they can be switched and also switch from multiple inputs to a series of outputs simultaneously. Configuring multiple switches to allow any input path to be switched to any output path of the switch enables the creation of a multiplexer or multiplexer. If only one input can be switched to a given output at a time, it is called a blocking matrix switch.

For example, switch matrices with more than 128 ports are available on the market for antenna array testing. Testing simple RF switches can be as simple as connecting the switch to a VNA and collecting transmission and reflection parameters from both ports in either switch state. For more complex switches, each port needs to be tested in each switch state. In some applications, it is also important to understand the dynamics of the switch during on-off and off-on switching actions to prevent a variety of peak loading conditions that could lead to undesired peak power levels seen on the device or signal path.

(ii) Impacting Performance Parameters

In addition to multi-port VNA testing of switches (which can be accomplished with a VNA with a switching matrix attachment), in some cases, signal generators and spectrum analyzers/power meters can also be used to test dynamic switching performance.

The key performance parameters typically specified for RF switches are as follows:

Impedance (on and off states)

Bandwidth

Insertion loss

Return loss (also known as overtemperature, referred to as IL temperature coefficient)

VSWR

Isolation

Crosstalk

Switching speed or switching time (rise time and fall time)

Power handling or RF input power (continuous wave or peak)

DC power dissipation

Positive operating voltage and bias (solid-state switching)

Thermal switching capability

Switch drive power/voltage/current or signal (can be analog or digital)

Reflection or termination

Input third order intercept (solid state)

Third order intermodulation (electromechanical)

1 dB compression point or 0.1 dB compression point

Minimum life in cycles

Operating Temperature Range

Since some RF switches are used in mission-critical applications, it is also critical to rigorously test the reliability and performance of the switches in extreme environments. In these cases, accelerated stress tests are often performed to determine the minimum operating life based on multiple switching cycles. In addition, some RF switches may require switching when signal power is applied, called thermal cutover, which can result in different power handling capabilities than switches in a static on or off position. For switches with multiple RF paths, it is critical to perform isolation testing using a multiport VNA, as some switch technologies may allow some signal power to leak from one path to another.