Components used in mobile-communication applications and radar systems often operate under pulsed or bursted conditions. Such components must be characterized under pulsed conditions to obtain valid measurement data. However, noise figure is one parameter that can only be determined under continuous-wave (CW) operating conditions when using conventional test equipment. In the application note, “Pulsed Noise Figure Measurements,” Rohde & Schwarz explains how to measure noise figure under pulsed conditions with spectrum analyzers and noise sources.
The technique described utilizes a signal and spectrum analyzer along with a broadband noise source that contains two temperature states. A function generator is also used to stimulate the device under test (DUT) with a pulsed signal. The noise source is connected to the input of the DUT, and the noise power at the DUT’s output is measured for each of the two input noise states.
The application note lists the three primary steps involved in making the measurement. The first step is doing the calibration, which leads to the second step of measuring the DUT cascaded with the test equipment. The last step is to calculate the DUT’s parameters with the cascaded noise-figure equation.
To determine the noise figure of an amplifier in pulsed operation, hot and cold power measurements must only be performed during the active part of the periodic pulse. Because the sampling process should only happen during the “on” phase of the pulse, a trigger signal is needed to synchronize the data acquisition of the spectrum analyzer with the “on” period of the pulse. A gated-sweep mode is used, meaning that data sampling only occurs during the active period of the RF burst.
A complete block diagram of the test setup for measuring pulsed noise figure is presented, followed by a detailed description of the entire procedure. Real pulsed measurement results are provided. In this test, the DUT is an amplifier used in a radar transmit/receive (T/R) module. The results demonstrate an agreement with the DUT’s performance when operating in CW mode.
Rohde & Schwarz, Mühldorfstrasse 15, 81671 Munich, Germany; (410) 910-7800.
