New measuring principles for pulsed-rf non-linear vectorial network analysers.

Project Details

Description

To build a good model of components and systems that work in the pulsed regime, measurements must be performed under the same circumstancces. Therefore a measurement system and new principles have to be disigned.

Design of new measurement principles in pulsed RF Nonlinear vectorial network analysers.

Philip Vael

Modelling Nonlinear systems in the RF domain is an hot topic during the last few years. Many components and systems work in pulsed mode to minimize the power consumption. Therefore, people want to model the Nonlinear effects which arise. To build a good model of components and systems that work in the pulsed regime, measurements must be performed under such working conditions. The goal is to extend the existing prototype of the 'Vectorial Nonlinear Network Analyser' for continuous wave measurements towards pulsed RF measurements. Therefore, we need:
to have a generator that produces a pulsed rf excitation signal. In figure 1, a possible setup for synthesizing and measuring a phase coherent pulsed rf signal is shown. A software feedback technique is used to have a full control over the spectral content of the excitation signal. Note that this generator has the advantage that phase coherence between carrier and envelope exist.

Measurement setup of the phase coherent pulsed rf signal generator
to determine the down conversion frequency in such a way that the spectral overlap, which may exist, is reduced to a minimum. A possible solution consist of optimizing the shape of the pulse in the frequency and time domain by using an appropriate window function. To choose a window function, the following issues has to be taken into account:
in the time domain, the top of the window has to be flat to approximate an ideal rectangular pulse,
in the frequency domain, the energy present in the side lobes has to diminish fast enough and to remain below the dynamic range of the instrument. This minimizes the number of spectral contributions present in the modulating pulse.
For these reasons, a flat-top window is chosen as pulse modulation signal. To minimize the spectral overlap of energy carrying lines, the down conversion frequency will be chosen such that:
all harmonics of the carrier are grouped around DC in the IF spectrum,
the nth modulation components of the upper and lower side band of each carrier harmonic are grouped in the higher part of the IF spectrum.
With this method, it is possible to measure the incident and reflected waves at both the input and output port of the DUT for a number of carrier harmonics together with the modulation spectra in one single measurement under pulsed rf excitation. From measurement data, the transient response of the device to pulsed signals can be visualized both in frequency and time domain. Measurement results of an amplifier shows that besides the nonlinear carrier, the behaviour of the modulation components (envelope) around the carrier harmonics is also available. These data can give more insight in the nonlinear pulsed rf operation of a device
to adapt the calibration. All measured energy carrying frequency components (i.e. the harmonics of the carrier plus their modulation spectra) has to be calibrated.

AcronymIWT13
StatusFinished
Effective start/end date1/01/9831/12/01

Keywords

  • Microwaves
  • Non-linear

Flemish discipline codes in use since 2023

  • Electrical and electronic engineering

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