Phaser
Mixer-Based, Vector-Corrected, Vector Signal/Network Analyzer Offering 300 kHz ? 20 GHz Bandwidth and Traceable Phase Response
Winner of the 2005 Macquarie University Innovative Partnership Award for its collaborative promotion of Department of Electronics and Agilent TechnolgiesProject Description
A measurement system has been developed that performs wide-bandwidth,
calibrated measurements of signals and components. It measures complex
modulated signals at two ports that are calibrated to an arbitrary reference
plane. A new hardware platform, which provides superior performance over the
existing methods has been developed. This includes increased sensitivity,
accuracy and improved bandwidth. The prototype, pictured right, uses a generator to
produce the multi-tone test signal that feeds signal to a source port.
The project has included the development of new standards that have been fully characterized by the National Institute of Standards and Technology, the national standards laboratory in the United States. Thus, the response is fully traceable to this national standards laboratory.
The system not only tests devices but provides additional information for better modeling and compensation of nonlinearity. This opens up opportunities for exciting applications, such as compensation of nonlinearity in power amplifiers, for example. Nonlinearity in microwave power amplifiers results in a trade-off between spectrum usage and power consumption. This measurement system can be used to reduce power consumption in base stations, which results in a reduction in the physical size and cost of telecommunications installations.
Applications
 Improving mobile phone base station efficiency |
 Testing of satellite communication links |
 Modeling of transistors |
Hardware
The block diagram of the measurement system is shown on the left, and a
photograph of the prototype appears above. The measurement system is based on
an Agilent N5230A 4-port, 20GHz linear VNA that has been modified for 2-port,
nonlinear operation. A five-channel receiver simultaneously acquires signals
from two directional networks associated with each of the two ports and a
phase reference. The phase reference is driven by a reference source that is
held at a single frequency for the duration of each measurement.
The system not only returns the magnitude spectrum, but also the phase spectrum of the signal being measured. The phase information can be useful for analysing distortion or wide-bandwidth Error Vector Magnitude (EVM). With wide-bandwidth magnitude and phase information, the measurement result can also be transformed to the time-domain, such that the crest factor can be calculated or combined signal and envelope clipping observed.
The measurement system operates in the frequency domain in a similar fashion to a spectrum analyser. A local oscillator (LO) is swept across a frequency range and the tones of interest are mixed to an intermediate frequency (IF) where they are sampled. In a traditional spectrum analyser, the local oscillator synthesiser is not phase-coherent and the phase is unknown. Therefore the phase information is only useful in the narrow bandwidth of the IF filter.
The measurement system has the advantage of recovering the phase information of the local oscillator and hence the measurement. The phase of the local oscillator is recovered by measuring a signal with known relative phase. In practice the known signal is a repetitive impulse in the time domain, which contains many tones in the frequency domain. The impulse is highly repeatable, and can be made traceable to NIST's electro-optic sampling system.
Measurement Examples
 (Test port 1) |
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(Test port 2) |
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The People
- Macquarie University (CNERF):
Agilent Technologies, Inc.: