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Building threat simulator for multi-port radar and warfare systems

Posted: 05 Dec 2011     Print Version  Bookmark and Share

Keywords:verification  router  simulation 

Each generator/AWG pair produces a complex waveform that simulates a combination of reference and offset signals. This is accomplished by defining two sets of complex waveforms in each two-channel AWG and using those signals to drive the I and Q wideband modulation inputs of the vector signal generator.

To simulate angle of arrival, the AWGs are loaded with multiple copies of the reference signal. Reference-channel memory is loaded with a single reference waveform while offset-channel memory contains multiple copies of the reference signal, each of which has a different phase offset (figure 2). The test executive simply calls up and plays the desired phase sequence.

Figure 2: Referencing the centerline, these 8-ns raised-cosine pulses have precise offsets of 90 and 180 degrees.

We created the individual waveforms using MATLAB from The MathWorks, based on Ashland-generated examples (figure 3).

Figure 3: MATLAB produced these 300MHz I and Q chirps.

Correcting amplitude, phase
On the measurement and feedback side of the system, a microwave network analyser measures the vector sum of the incident and reflected waveforms at the UUT inputs. The network analyser uses those measurements to compensate for system drift and UUT mismatch with the test system. The UUT test cables represent the largest contributor to system drift.

The calibration pods maintain analyser calibration over time and temperature. This capability is enabled by performing a system calibration (after all cables have been connected) using electronic calibration modules, which the network analyser controls through a USB connection. Because the calibration pods are always in the signal path, the initial calibration captures their characteristics and uses them as a baseline for calculating the corrections that will be applied whenever a refresh is performed. With this capability, the test executive can direct the analyser to refresh its calibration during testing without requiring a reconnection of the calibration devices.

This process makes a key contribution: The system "knows" the actual phase and amplitude of the test signals at the UUT inputs. Previously, the reference point was the output of the signal generator; however, environmental changes can have a profound effect on cable length over the required range of test frequencies. The configuration used here accounts for changes between the paths and, through the test executive, commands the AWG to play a signal that provides the desired phase offset at the UUT.

The deployed system has met or exceeded expectations from both the technical and operational perspectives. On the technical side, there are five key accomplishments:
 • Can produce virtually any known radar pulse
 • Requires a single set of four connections per UUT
 • Achieves accuracy of less than 1 degree at the UUT
 • Provides resolution on the order of milli-degrees
 • Delivers on/off ratios of 100 dB or greater

From an operational perspective, the system provides three key benefits. Perhaps most strikingly, it reduces setup time from days to minutes. The other two benefits are related: hands-free calibration minimises operator intervention, and the autonomous operation cuts the cost of test.

As a final note, the system could be expanded beyond four ports using test sets that provide as many as 22 ports. Custom and high-power test sets are also available.

About the author
John Eckert is an Application Engineer in the electronic measurement group at Agilent Technologies, supporting the RF and MW product lines. He provides customer support through training classes and consultation. John has been in this role since 1987 when he joined Hewlett Packard's Test and Measurement Group. Previously, John held engineering positions in manufacturing and engineering at General Electric. John has also provided support for Agilent Lightwave products and holds a patent in that field. John has a B.S.E.E. from Oakland University, Rochester, Michigan.

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