Get to know RF switch specifications
Martin Rowe, Senior Technical Editor -- Test & Measurement World, 10/1/2007
RF switches—like all other components of a transmission system—degrade signals. Signal degradation can become significant at frequencies above 1 GHz. At 3 GHz, the signal loss intensifies further.
You may assume that an RF switch's bandwidth is the 3-dB point, the point where output signal power drops to 50% of that level at lower frequencies. Not so when it comes to RF switches, argues Jaideep Jhangiani, product manager for switches at National Instruments. In a paper titled “Understanding RF Switch Specifications,” Jhangiani explains that “bandwidth is the highest-frequency signal that the manufacturer believes you can route through the product with acceptable performance.”
| Download “Understanding RF Switch Specifications.” |
In the paper, Jhangiani explains that bandwidth isn't the only specification you should investigate in an RF switch. He describes how the characteristics of a transmission line affect signal integrity. Specifications include impedance, insertion loss, voltage-standing wave ratio, isolation, and crosstalk in addition to bandwidth. Throughout the paper, Jhangiani uses equations and figures to show how each of these characteristics affect signals and why they're important.
The figure shows how switches can attenuate signals. Assume that the input signal is a 3-GHz sine wave. At that frequency, significant loss can occur. Because attenuation may be nonlinear, you should look at a switch's entire frequency-response curve to find the best switch for your application.
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RF switches attenuate the amplitudes of high-frequency signals. |
