Universal-serial-bus (USB) connections have greatly simplified the operation of a personal computer (PC) with peripheral devices, such as keyboards and printers. A USB connection can also make it easier to perform RF/microwave power measurements, by simply connecting an ST Series power sensor from Satori Technology (Lanarkshire, Scotland) to a PC. The USB power sensors contain all the circuitry needed for CW power measurements through 18.5 GHz and at power levels from −50 to +20 dBm.

The ST Series USB power sensors (see figure) are small, but contain the equivalent of a complete power meter and sensor, including a microprocessor. Satori is currently shipping two versions of the USB power sensor: the ST124SMA with frequency range from 10 MHz to 12.4 GHz and the ST185SMA with frequency range from 10 MHz to 18.5 GHz. Both have SMA (male) connectors for attachment to an RF/microwave device under test.

An operator controls one of the ST Series USB power sensors from the graphical user interface (GUI) of the easy-to-use software provided with each sensor. The software, which is written for the Microsoft Windows XP operating system, features a control panel as well as virtual instrument display screens showing plots of power versus time, frequency, and other formats. A single laptop or PC can run multiple ST Series sensors, depending on the number of available USB ports. Each sensor is shipped with a software toolkit that includes a .dll (dynamic link library) file for customizing the sensor with a user's computer. Additionally, examples of Agilent Vee and National Instruments LabView are shipped on the CD.

Because they measure only 1.9 x 1.2 x 6.7 in. (34 x 43 x 125 mm) and weigh only 83 g, the power sensors are ideal for production environments. In spite of their small size, they are fully functional power meters/sensors and capable of high levels of accuracy through 18.5 GHz. Measurement speed is important in production, and the ST Series sensors deliver 8 measurements per second for power levels from −50 to −35 dBm, 33 measurements per second for power levels from −35 to −20 dBm, and 50 measurements per second for power levels from −20 to +20 dBm.

The measurement accuracy also belies the size of the ST series sensors. Without needing a reference calibrator, both sensors exhibit linearity errors at room temperature (+25°C) of ±0.27 dB for measurements from −40 to +10 dBm at 50 MHz and ±0.49 dB for measurements from +10 to +20 dBm at 50 MHz. The calibration factor errors (at room temperature) for both sensors is ±0.24 dB for frequencies from 10 MHz to just less than 50 MHz, ±0.19 dB from 50 MHz to 4.5 GHz, ±0.23 dB from 4.5 to 8.5 GHz, and ±0.32 dB from 8.5 to 12.4 GHz. For the ST185SMA, the calibration-factor error is ±0.38 dB for frequencies from 12.4 to 18.5 GHz.

The power sensor draws about 50 mA from the USB port. Each sensor is provided with software on a compact disk (CD), a 6-ft.-long USB sensor cable, and an operator's manual. Additional accessories include coaxial adapters, attenuators, and a 6-ft.-long sensor cable. Satori Technology Ltd., 1 Biggar Business Park, Biggar, Lanarkshire ML12 6FX, Scotland ; 44 (0) 1899-229-258, FAX: 44 (0) 870-330-5884, e-mail: sales@satori-technology.com, Internet: www.satori-technology.com.