In microwave testing systems, RF and microwave switches are widely used for signal routing between instruments and DUTs. By placing the switch into the switch matrix system, signals from multiple instruments can be routed to one or more DUTs. This allows for multiple tests to be completed using a single testing device without the need for frequent disconnection and reconnection. And it can achieve automation of the testing process, thereby improving testing efficiency in mass production environments.
Key performance indicators of switching components
Today’s high-speed manufacturing requires the use of high-performance and repeatable switch components in testing instruments, switch interfaces, and automated testing systems. These switches are typically defined according to the following characteristics:
Frequency rangeThe frequency range of RF and microwave applications ranges from 100 MHz in semiconductors to 60 GHz in satellite communications. The testing attachments with wide working frequency bands have increased the flexibility of the testing system due to the expansion of frequency coverage. But a wide operating frequency may affect other important parameters.
Insertion lossInsertion loss is also crucial for testing. A loss greater than 1 dB or 2 dB will attenuate the peak level of the signal, increasing the time of the rising and falling edges. In high-frequency application environments, effective energy transmission sometimes requires a relatively high cost, so the additional losses introduced by electromechanical switches in the conversion path should be minimized as much as possible.
Return lossThe return loss is expressed in dB, which is a measure of the voltage standing wave ratio (VSWR). Return loss is caused by impedance mismatch between circuits. In the microwave frequency range, material characteristics and the size of network components play an important role in determining impedance matching or mismatch caused by distribution effects.
Consistency of performanceThe consistency of low insertion loss performance can reduce random error sources in the measurement path, thereby improving measurement accuracy. The consistency and reliability of switch performance ensure measurement accuracy, and reduce ownership costs by extending calibration cycles and increasing testing system operation time.
IsolationIsolation is the degree of attenuation of useless signals detected at the port of interest. At high frequencies, isolation becomes particularly important.
VSWRThe VSWR of the switch is determined by mechanical dimensions and manufacturing tolerances. A poor VSWR indicates the presence of internal reflections caused by impedance mismatch, and the parasitic signals caused by these reflections can lead to inter symbol interference (ISI). These reflections typically occur near the connector, so good connector matching and correct load connection are critical testing requirements.
Switching speedThe switch speed is defined as the time required for the switch port (switch arm) to go from “on” to “off”, or from “off” to “on”.
Stable timeDue to the fact that the switching time only specifies a value that reaches 90% of the stable/final value of the RF signal, stability time becomes a more important performance of solid-state switches under the requirements of accuracy and precision.
Bearing powerThe bearing power is defined as the ability of a switch to carry power, which is closely related to the design and materials used. When there is RF/microwave power on the switch port during switching, thermal switching occurs. Cold switching occurs when the signal power has been removed before switching. Cold switching achieves lower contact surface stress and longer lifespan.
TerminationIn many applications, a 50 Ω load termination is crucial. When the switch is connected to an active device, the reflected power of the path without load termination may damage the source. Electromechanical switches can be divided into two categories: those with load termination and those without load termination. Solid state switches can be divided into two types: absorption type and reflection type.
Video leakageVideo leakage can be seen as parasitic signals appearing on the switch RF port when there is no RF signal present. These signals come from the waveforms generated by the switch driver, especially from the front voltage spikes required to drive the high-speed switch of the PIN diode.
Service lifeLong service life will reduce the cost and budget constraints of each switch, making manufacturers more competitive in today’s price sensitive market.
The structure of the switch
The different structural forms of switches provide flexibility for building complex matrices and automated testing systems for various applications and frequencies.It is specifically divided into one in two out (SPDT), one in three out (SP3T), two in two out (DPDT), etc.
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