An Active Load-Pull Setup for Broadband Signals Using Digital Baseband Processing for the Active Loop
An active load-pull system for broadband signals is presented. The forward traveling output signal of the device under test (DUT) is demodulated to an intermediate frequency (IF), digitized, processed in digital baseband, up-converted again, and injected as the backward traveling wave. By using periodic signals and sampling of exactly the entire period in a fully synchronous setup, it is possible to correct the frequency response over the entire measurement bandwidth and to compensate timing delays with minimum mathematical effort. In contrary to active load pull systems with closed-loops the proposed setup can perfectly compensate all errors and maintain a constant phase over the entire band-width of the broadband signal. Therefore, no signal distortion will occur and parameters like adjacent channel power ratio (ACPR), error vector magnitude (EVM), etc. can be measured accurately. (C) 2008 Wiley periodicals. Inc. Int J RF and Microwave CAE 18: 574-581, 2008.
broadband baseband processing active loop load pull