Changes

</ul>

Make sure the GPIB-USB cable from the back panel of lock-in amplifier and the USB cable from the X-axis translation stage are connected to the [[NeoScan]] USB Hub.

The [[NeoScan]] system designates C:\Users\[[NeoScan|neoscan]]\Documents\[[NeoScan]]\Projects as the parent folder in which all data files from a scan will be saved as project folders in this directory.

Create a project folder by entering the title in Project Name Entry Box and pressing “Create Folder” button.

Select the operation frequency from the box labeled “Frequency.”

Set the “Calibration Factor.”

“Project Description” editor enables a user to create and edit a text file.

The project name should have a maximum of 25 characters. Do not use “Empty Space” or any of the following characters: ` ! @ " # $ % ^ & * ( ) + = \ | / { } [ ] , > < : ; ?. Note that it is allowed to use “dot” in project name, for example, you can choose patch_2.349GHz as your project name.

When you start [[NeoScan]] Mapping Utility program a folder called “Untitledproject” is created automatically in parent folder. Failed to press “Create Folder” button, all data files will be written in “C:\Users\[[NeoScan|neoscan]]\Documents\[[NeoScan]]\Projects\Untitledproject” folder (Figure 4.4). A user can rename the files appropriately after [[NeoScan]] Mapping Utility program is stopped.

It is assumed that the users are familiar with the operation of the “Translation Stage.” Otherwise, it is highly recommended that you read Appendix A-I. Press “Hardware Settings” tab in [[NeoScan]] Mapping Utility interface (see Figure 4.5).

Set lock-in amplifier parameters:

Select the Lock-in Amplifiers for each channel using the Lock-in Amplifier Selector and set their corresponding parameters.

Put down the Visa menu and select the appropriate GPIB address for lock-in amplifier Visa The default is GPIB0::8::INST.

Set lock-in amplifier sensitivity. The sensitivity of lock-in amplifier is the rms amplitude of an input sine (at the reference frequency) which results in a full scale DC output (10Vdc).

Select “Time Constant” from the dropdown lists. The default for time constant of the output low-pass filter that determines the bandwidth of lock-in amplifier in 10 ms.

Press “Update Settings” button to reload new values when you make changes. The system will respond with "Updated settings" message in information panel to confirm the settings if the values are appropriate. Otherwise, it asks you to check the parameters.

 

Other parameters that should be directly set on SR844 RF lock-in amplifier – since they are not controlled (see Figure 3.13 in section 3.2.2):

Time constant: 24 dB/oct

Sensitivity: Low noise

X display: R(dBm)

Y display: θ

The signal levels at the Signal In port on the Lock-in amplifier are in the range of -100 dBm to -40 dBm or higher, depending on device one measures. It is important to set the sensitivity of the Lock-in amplifier greater than the expected input signal amplitude at the Signal Input port (from the IF Out of the optical mainframe). For example, if you expect a signal less than -67 dBm but greater than -87 dBm, set the sensitivity to -67 dBm and 100 μV (rms) setting. If the input signal is greater than the input signal setting, an OVERLOAD condition will occur and the red LED OVERLOAD indicators on the Lock-in amplifier will flash.

Make sure the GPIB-USB cable from the (back panel of) each lock-in amplifier is connected to the USB Hub.

If the largest tolerable noise signal (at the input) exceeds the full scale signal, the red LED OVLD indicators in lock-in indicate that the readings may be invalid due to an overload condition. In this situation, you many try increasing the time constant or to use a larger full scale sensitivity.

To set translation stage speed settings:

From “Visa COM” serial port drop-down list select the COM port that the X Linear Translation Stage is connected to. A COM port is a specific serial connection on a computer, such as COM3.

Set the probe height – the distance between the probe and the DUT surface – using the knob (Figure 4.7). If you are interested in high resolution scanning, you may skip the other parameters, which will be discussed later in the chapter on Far Field Measurements.

In order to scan the distribution of electric field on a DUT, three parameters are needed to be known:

Dimensions of the probed (scanned) area in X and Y directions (D_PX, D_PY);