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NSIFAQsNSI2000

FAQ Topics

NSI 2000 Software FAQ

1. How accurate is the open-ended waveguide probe model included in the NSI 2000 software?

2. Is the NSI 2000 software capable of controlling a beam steering computer (BSC) during a scan?

3. How is the peak FF value determined in the NSI 2000 software?

4. Does the NSI software integrate over the measured radiation patterns to obtain the directivity (ie the usual way of obtaining directivity)?

5. How does the NSI 2000 software calculate the S/N signal-to-noise value in the real time monitor display?

6. What version of NSI 2000 is required for Windows 64-bit operation?


1. How accurate is the open-ended waveguide probe model included in the NSI 2000 software?

The OEWG probe model is based on a NIST algorithm (Yaghjian-1983). The model provides a far-field prediction of an open-ended waveguide probe with an accuracy of approximately 0.15 to 0.4 dB over +/- 60 degrees in Elevation and Azimuth.

Click here to see a comparison of the NSI2000 OEWG model with measured probe data.

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2. Is the NSI 2000 software capable of controlling a beam steering computer (BSC) during a scan?

Yes, with open-loop (output only) control. The standard NSI 2000 software does not support BSC handshaking, but it can be added as an option. The standard open-loop capability can be configured to output a bit pattern (typically up to 8-bits, TTL output - more bits may be provided with customization), which may be used by the BSC to control pre-defined beam states.

The open-loop timing may be verified using the NSI 2000 inner-loop timing (ILT) display capability. The ILT display shows all beam running at the defined switching rate so that amplitude, phase and SNR may be verified at a fixed XY position in the high energy region of the antenna. If there is a timing or interface problem, the measured data will exhibit erratic behavior.

Full handshaking with the BSC requires a custom interface and typically involves technical coordination between NSI and the customer to define the hardware and software interfaces. Contact the NSI sales department for a quotation.

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3. How is the peak FF value determined inthe NSI 2000 software?

In the NSI 2000 software there is a result that is referred to as 'far-field peak' when the far-field is computed. This value is related to gain and is described more fully in the article written by Allen Newell, Far-Field Peak in NSI Programs.

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4. Does the NSI software integrate over the measured radiation patterns to obtain the directivity (ie the usual way of obtaining directivity)?

NSI 2000 does calculate directivity in the “usual” surface integral way. Some extra detail re. polarization: The NSI 2000 program uses the output from the spherical wave expansion code after converting from theta phi components to the polarization components specified in the far-field menu. This data array always covers the complete sphere and so the integration of the pattern to obtain the radiated power is always over the full sphere regardless of the far-field spans in the far-field menu. As defined by international standards, both gain and directivity are total power quantities and are defined in terms of the total power per unit solid angle and therefore should be independent of the polarization components used to represent the field or the polarization of the antennas used to measure the field. In almost all uses of gain standards however, the quantity of most value is the partial gain for the main component of the antenna. Since in most cases the cross polarization of the antenna is small at the peak of the beam, the actual difference between the total power gain and the partial gain is very small. In the NSI software, the gain values are always partial gain values and use only the peak far-field values for the main component. To be consistent, the calculated directivities also use only the peak far-field values for the main component and the total radiated power is calculated by integrating only the main component pattern. You can see how this affects the directivity by changing the polarization sense from linear to circular. The peak far-field values will change, and generally the directivity will also change.

We do have a script that would calculate total power directivity, and you should see no change in the results when you change the polarization sense. The script was developed to check the directivity calculations and we could modify it to calculate either total power directivity or partial directivity. The current version calculates total power directivity and if that quantity is desired, the script can be used. For partial directivity, the NSI 2000 results are correct.

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5.How does the NSI 2000 software calculate the S/N signal-to-noise value in the real-time monitor display?

The real-time S/N level is determined by monitoring the amplitude variation over time and then computing the corresponding Error/Signal (E/S) level required to cause that level of amplitude variation. The noise is treated as an error relative to a peak, or perfect, signal and may be represented in one of two ways: either as an uncertainty in amplitude or as an error below the signal peak. As shown in the plot below, a small variation in amplitude, or uncertainty, results in an exponential change in the E/S level, or S/N. The S/N value in the NSI 2000 real-time monitor is a convenient method of conveying the actual noise level, relative to the signal, currently present in the measurement.

The table shows the uncertainty for various S/N levels. Note that the a 20 dB improvement in S/N reduces the uncertainty by factor of 10. The exponential nature of the relationship is shown in the plot.

S/N (dB)
Uncertainty (dB)
10
±3
20
±1
30
±0.3
40
±0.1
50
±0.03
60
±0.01

 

 

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6. What version of NSI 2000 is required for Windows 64-bit OS operation?

NSI 2000 v4.6.3 or later is supported on Windows 64-bit OS, but for V4.6.x versions will require the latest USB key software driver from Aladdin. The driver (hldrv32.zip) can be downloaded online from:
http://www3.safenet-inc.com/support/hardlock/downloads.aspx

NSI 2000 V4.7.x or later will include the USB key driver with the installation.

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