Overview of Coaxial and Cable-Mounted Probes


In the prototyping and testing phases of RF equipment, testing at non-port locations within the circuit is often essential for optimizing design or troubleshooting. However, when dealing with higher frequencies, testing becomes more challenging due to the impedance mismatch between the RF transmission line and the voltage probe.high voltage probe The insertion of a common voltage probe can result in significant deviations in test results.

To address this issue, RF test probes must impedance match the test points. Typically, this is achieved by soldering coaxial cables (pigtails) to pre-planned test points in the design. This ensures proper impedance matching and allows the selection of test points in areas that have minimal impact on overall design performance.wafer chuck Alternatively, dedicated RF probes can be soldered to customized pads or lead designs to reduce intrusive testing. While high-performance test equipment suppliers offer specialized probes for frequencies up to millimeter waves, these probe tips can be expensive and may not consistently provide access to the circuitry, making them more suitable for prototyping and development rather than high-volume test applications or troubleshooting.

Companies also have alternative options, including wafer probe stations, matching pogo-pin probes, or flexible probes through other methods. Calibration cards, calibrated at the test point (close to the exact probe position), play a crucial role in maintaining accuracy, with minimal impact from probe technology.manual prober One emerging option is the use of coaxial RF cable-mounted probes, which combine the precision and repeatability of probe bench setups with the accessibility of specialized probes.

These cable-mounted probes feature edges similar to a probe table fixture, with configurations like ground-signal-ground (GSG) or ground-signal (GS). One end is equipped with a pogo-pin probe, while the other end has a typical coaxial connector. Capable of reaching 40 GHz with a return loss better than 10 dB, these probes offer pin spacings ranging from 800 µm to 1500 µm and are typically terminated with 3.5 mm female or 2.92 mm female coaxial connectors. Similar to probe benches, a pad port can be designed to minimize impact in a specific test area, or the probes can be strategically placed on terminals or microstrip transmission lines close to the component.

Cable-mounted probes can be utilized manually or with a multi-axis probe positioner. Unlike conventional probe stations, these probes are large enough for manual operator use and exhibit high reliability. The probe positioners offer enhanced positional accuracy and repeatability and can be easily positioned for testing. In contrast to probe stations, coaxial cable-mounted probes and positioners are versatile tools, serving as network analyzers, signal generators, spectrum analyzers, oscilloscopes, and other accessories for RF microwave, millimeter-wave, and high-speed digital applications on an engineer or technician's typical test bench. The compact, non-destructive, and non-invasive design of cable-mounted RF probes allows testing in high-density applications, such as antenna arrays, metamaterials, fractal antennas, microstrip transmission lines, compact components, and printed circuit boards with small surface-mount packaged components.

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