Electronics Weekly
It is based on the company’s RTP084 scope, equipped with the wide-band modulated load-pull option (RTP-K98) and paired with its SMW200A vector signal generator.
“By enabling load pull with wide-band modulated signals, it allows precise validation of performance indicators across varying impedances, such as EVM [error vector magnitude] and ACLR [adjacent channel leakage ratio],” said R&S. “The oscilloscope’s internal architecture guarantees absolute phase and time synchronisation for forward and reverse wave measurements. The dual path vector signal generator offers accurate timing and phase stability between the input and tuning signal for load pull operation.”
RTP-K98 software processes the oscilloscope’s data, performs calculations needed to achieve the target impedance, and controls the signal generator.
The RTP oscilloscope can acquire and processing 750,000waveform/s, 3Gpoint/channel can be acquired, and embedded clocks can be recovered at up to 16Gbit/s.
“Our approach for wide-band modulated load pull utilises standard test instruments [and addresses] the need for verifying wide-band RF front-ends across varying impedances, as experienced in wideband antenna usage,” said Rohde & Schwarz RF components manager Markus Lörner. “The incorporation of the oscilloscope as the key instrument offers rapid wide-band signal capture.”
A traditional modulated load pull solution validates modulation characteristics under different impedances using a vector signal generator and vector signal analyser. A passive tuner is used to simulate different load conditions.
This method has several limitations, claimed R&S: there is a significant frequency response and group delay of the tuner in amplitude and phase leading to measurement uncertainties. “While these may be ignored for narrowband applications, they become significant for higher signal bandwidths, typically around 100 MHz and above.”
Applications are foreseen with RF front-ends that are used over wider frequency ranges and multiple transmission bands, such as 5G or Wi-Fi.
