U.S. patent application number 12/857004 was filed with the patent office on 2011-02-10 for antenna near-field probe station scanner.
Invention is credited to Philip J. Barr, William G. Darby, Kevin M. Lambert, Richard Q. Lee, Felix A. Miranda, Afroz J. Zaman.
Application Number | 20110032253 12/857004 |
Document ID | / |
Family ID | 43479780 |
Filed Date | 2011-02-10 |
United States Patent
Application |
20110032253 |
Kind Code |
A1 |
Zaman; Afroz J. ; et
al. |
February 10, 2011 |
Antenna Near-Field Probe Station Scanner
Abstract
A miniaturized antenna system is characterized non-destructively
through the use of a scanner that measures its near-field radiated
power performance. When taking measurements, the scanner can be
moved linearly along the x, y and z axis, as well as rotationally
relative to the antenna. The data obtained from the
characterization are processed to determine the far-field
properties of the system and to optimize the system. Each antenna
is excited using a probe station system while a scanning probe
scans the space above the antenna to measure the near field
signals. Upon completion of the scan, the near-field patterns are
transformed into far-field patterns. Along with taking data, this
system also allows for extensive graphing and analysis of both the
near-field and far-field data. The details of the probe station as
well as the procedures for setting up a test, conducting a test,
and analyzing the resulting data are also described.
Inventors: |
Zaman; Afroz J.;
(Strongsville, OH) ; Lee; Richard Q.; (Ann Arbor,
MI) ; Darby; William G.; (Litchfield, OH) ;
Barr; Philip J.; (Schiller Park, IL) ; Lambert; Kevin
M.; (North Royalton, OH) ; Miranda; Felix A.;
(Olmsted Falls, OH) |
Correspondence
Address: |
NASA GLENN RESEARCH CENTER;Robert H. Earp, III
21000 BROOKPARK ROAD, MAIL STOP 21-14
CLEVELAND
OH
44135
US
|
Family ID: |
43479780 |
Appl. No.: |
12/857004 |
Filed: |
August 16, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11499982 |
Aug 2, 2006 |
|
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|
12857004 |
|
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Current U.S.
Class: |
345/419 |
Current CPC
Class: |
H01Q 3/08 20130101; G01R
29/105 20130101 |
Class at
Publication: |
345/419 |
International
Class: |
G06T 17/00 20060101
G06T017/00 |
Goverment Interests
STATEMENT OF GOVERNMENT INTEREST
[0002] The invention described herein was made by civil servant
employees of the United States Government, and a non-civil servant
employee working under a NASA contract, and is subject to the
provisions of Section 305 of the National Aeronautics and Space Act
of 1958, Public Law 85-568 (72 Stat. 435; 42 U.S.C. 2457).
Claims
1-14. (canceled)
15. A computer readable program stored in a tangible medium, said
program comprising instructions for producing a grid work pattern
of near-field signals radiated from a miniature antenna and for
characterizing the far-field behavior of the antenna based upon the
captured signals, comprising: a. A management software package
having the keyed-in capability of controlling other embedded
software packages; b. An embedded software package that is
controlled by the management software package and that is useful in
mathematically performing a near-field to far-field transform; and
c. A visual software package that is controlled by the management
software package and that has the capability of displaying
near-field phase and magnitude plots and for showing three
dimensional, contours, vertical cuts and horizontal cuts through
the far-field pattern distribution of the antenna based upon the
transforms performed by the mathematical software package.
16. The computer readable system according to claim 15 wherein the
management software package includes a screen, means for the entry
of scan parameters, including grid pattern to be used for taking a
plurality of near-field measurements using a RF scanning probe, for
moving said scanning probe to each measurement location within the
grid, and for taking and recording each measurement.
17. The computer readable system according to claim 15 wherein the
medium is selected from the group consisting of a floppy disc, a
compact disc, a hard disc, a RAM a RUM, and combinations
thereof.
18. A software system for capturing the near-field power
performance characteristics of a miniature antenna, for
transforming the near-field characteristics to far-field
properties, and for displaying the near-field and far-field
performance patterns, comprising: a. A management software package
having the keyed-in capability of controlling other embedded
software packages; b. An embedded software package that is
controlled by the management software package and that is useful in
mathematically performing a near-field to far-field transform; and
c. A visual software package that is controlled by the management
software package and that has the capability of displaying
near-field phase and magnitude plots and for showing three
dimensional, contours, vertical cuts and horizontal cuts through
the far-field pattern distribution of the antenna based upon the
transforms performed by the mathematical software package.
19. The software system according to claim 18 wherein the
management software package includes a screen for the entry of scan
parameters including a grid pattern, for inputting the linear and
rotational movement patterns of the scanner probe within the grid,
for taking and recording each measurement, and for determining the
status of the scan.
20. The software system according to claim 18 wherein the
mathematical software package utilizes a two dimensional fast
Fourier equation to make the transform.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. patent application
Ser. No. 11/499,982, filed Aug. 2, 2006, the entire disclosure of
which is hereby incorporated by reference herein.
FIELD OF THE INVENTION
[0003] The present invention relates generally to a scanner device
for the measurement of miniaturized antennas using near-field
signals. More particularly, it relates to a probe station scanner
for measuring near-field radiated power performance of a
miniaturized antenna, and for transforming the measurements into
far-field characteristics.
RELATED ART
[0004] Before an antenna can be used for a particular application,
the antenna must first be tested to determine its performance
characteristics. One characteristic, the radiation pattern, is
generally tested in an antenna range. Antenna range types are
numerous, and the choice of range to use is dependent on many
factors. Antenna size, frequency of operation, mechanical
supporting requirements and the intended application are but a few
of the factors. For example, an electrically large antenna that
must be tested indoors, requires the use of a near-field scanning
range. Alternatively, a similar, but electrically smaller antenna
may be able to utilize a far-field range. Smaller yet, miniaturized
antennas impose additional requirements not addressed by the
conventional ranges and hence require a new approach.
[0005] Space exploration systems require the use of miniaturized
antennas for surface networks and planetary exploration
communication. In addition, miniaturized antenna systems find use
in cellular telephones, various wireless connections, and a variety
of embedded medical circuits for diagnostics and treatment.
Generally, a large number of these antennas are produced on a
single wafer much like semiconductor devices. Probe stations, used
for semiconductor device characterization, can also be used to
obtain antenna patterns when the devices are antennas. Doing so
allows the antennas to be tested on wafer enabling a number of
advantages over a more conventional technique. Conventionally the
antennas must be separated using a procedure that is very time
consuming and expensive. Then the single antenna must be placed in
a fixture for testing. The antenna must be isolated from the
fixture, or the fixture will adversely effect the characterization.
Accordingly, the conventionally tested results do not always
produce the true radiation pattern of the antenna.
BRIEF DESCRIPTION OF THE INVENTION
[0006] To facilitate the understanding of the present invention,
these abbreviations will have the following definitions, unless
otherwise provided within this document.
[0007] AUT antenna under test
[0008] CPU central processing unit
[0009] CW continuous wave
[0010] DC direct current
[0011] FFT fast Fourier transform
[0012] Gain amplification factor; a boost in signal strength
[0013] G-S-G ground-signal-ground
[0014] GUI graphical user interface
[0015] MEMS micro electro-mechanical system
[0016] RF radio frequency
[0017] VNA vector network analyzer
[0018] This invention provides the capability for characterizing
miniaturized antennas while biasing any necessary active (e.g.,
MEMS) devices. This is conducted by measuring the near-field
patterns of small micro-channel patch antennas. Each antenna is
excited using a probe station system while a waveguide scans the
space above the antenna to measure the near-field signal. Upon
completion of the scan, the near-field patterns are transformed
into far-field patterns. Along with taking data, this system also
allows for extensive graphing and analysis of both the near-field
and far-field data. The procedures for setting up a test,
conducting a test, and analyzing the resulting data are also
described.
[0019] The invention comprises a near-field probe station and its
use for scanning the near-field radiated pattern of a miniaturized
printed circuit antenna. The probe station comprises a three axis
probe slide and rotation platform. A coplanar waveguide and RF
probe are mounted to move along the three axes to provide input
signals to the antenna under test. The station may also include a
DC probe to apply a DC bias to the antenna being tested. A network
analyzer such as an HP8510C and a computer are also included. A
software program is usable with the computer for the analysis of
near-field data collected with the scanner. This program is capable
of displaying three dimensional contours of the far-field pattern
distribution of the antenna.
[0020] The invention also includes a software system for capturing
the near-field signals from a miniature antenna and for
characterizing the actual behavior of the antenna based upon the
captured signal. This system comprises a management software
package having the keyed-in capability of calling up other software
packages embedded therein. It also includes two embedded software
packages. The first package is useful in making a near-field to
far-field transform. The second package is a visual package having
the capability of showing three dimensional, contours, vertical
cuts and horizontal cuts through the far-field pattern distribution
of the antenna.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] The drawings as described herein are presented for the
purpose of illustrating the invention, and its environment, and are
not intended to serve as a limitation on the invention.
[0022] FIG. 1 is a flowchart of a computer program for
characterizing miniature antennas;
[0023] FIG. 2 is a schematic of the antenna scanner;
[0024] FIG. 3 is a layout showing the hardware components of the
present invention;
[0025] FIG. 4 shows a panel for control of the operation of the
scanner;
[0026] FIG. 5 is a three-dimensional graph of a near-field
magnitude plot;
[0027] FIG. 6 is a near-field phase plot;
[0028] FIG. 7 is a far-field transform of the data shown in FIGS. 4
and 5;
[0029] FIG. 8 shows contour plots of the Far Field Magnitude;
and
[0030] FIG. 9 is a top view showing multiple antennas on a single
wafer.
DETAILED DESCRIPTION OF THE INVENTION
[0031] The present invention relates to antenna metrology hardware
for non-destructive characterization of miniaturized passive or
active antennas fabricated on substrates (e.g., Gallium Arsenide
(GaAs), Silicon (Si), Lanthanum Aluminate (LaAlO.sub.3, etc.) which
are difficult to measure in traditional ranges because of their
smaller size, fragility, and non-trivial DC biasing or complicated
fixturing requirements. For the purposes of the present invention,
miniaturized antennas are those having a dimension of about 1 cm or
less, down to 1 mm or even smaller. Stated differently, these small
antennas have a cross sectional size of about 1/5 to about 1/2
lambda, whereas large antennas have a size greater than 1/2 lambda.
The scanner consists of a precision mechanical slide system,
software analysis features, a probe station, and an automatic
network analyzer. The turn-key antenna near-field data acquisition
system in this scanner is extremely fast, automated, and user
friendly. It only requires user information to be entered via
soft-keys into the input control panel.
[0032] Other functionalities of the invention include
report-quality image storage for publication purposes, accessible
data files for further future processing, and text documentation
associated with each data folder describing the test parameters and
test conditions. Compared to other conventional ranges, this
scanner offers considerable cost savings, reduces prototype
characterization time from months to days, does not require a
separate stand-alone data analysis and graphic visualization
platform, and is particularly suitable for characterization of
miniature antennas.
[0033] A simplified flowchart of the computer program for
controlling the various functional features of the invention is
shown in FIG. 1. A scan is started at 10 by inputting a command
from a computer keyboard. In the first step (12), the computer
establishes a communication link with a scanning probe (described
in the flow sheet as a waveguide probe) and with the ground surface
ground (G-S-G) microwave probe at the probe station. In the second
step (14), a rectangular matrix of grid points for the near-field
data acquisition is provided to the probe station. In step 3 (16),
an RF signal is applied to the AUT through the G-S-G probe. Also,
to the extent required, a DC bias is applied at 18 to any bias pads
on the ALIT through the DC probe. Step 4 activates the 3-axis probe
slide and probe rotation device at 20 to move the device to the
various grid points established in Step 2 to record data at each
point. In step 5 (22), the computer controls the collection,
analysis and visualization of the data collected in Step 4. In step
6 the data is converted or transformed (24) by the use of a FFT
into the actual far-field pattern.
[0034] The invention features software which accesses commercially
available software codes such as LabVIEW, Visual Basic, and Matlab
to analyze the measured near-field data to be able to display
far-field antenna patterns either in 3-dimensional, contour form,
or as vertical or horizontal cuts through the antenna's far-field
pattern distribution. LabVIEW is a graphical programming software
tool available from National Instruments. Visual Basics is a tool
to aid in the development of a wide range of applications based
upon the NET framework, and is available from Microsoft. MATLAB is
a matrix algebra software package that utilizes various algorithms
for numerical experiments, graphics and calculations. It is
available through The Mathworks, Inc.
[0035] Space exploration systems require miniaturized antennas for
surface networks and planetary exploration communication. Thus, for
design and optimization of prototype antenna candidates for these
uses, an effective, fast, and reliable characterization capability
is required. The near-field probe station scanner of the present
invention provides non-destructive characterization of small
passive and active antennas, fabricated on semiconductor and, or
dielectric wafers (e.g., GaAs, Si, LaAlO.sub.3, etc.).
[0036] The near-field probe station scanner includes a near-field
data acquisition feature that allows for maximum power capturing
and therefore is very suitable for characterizing miniature
antennas with low gain. This capability allows the characterization
of prototype antennas, either of a single design, multiple variants
of one design, or multiple antenna designs on the same substrate in
one session. This is achieved without the requirement for dicing or
packaging of the substrate, and no test fixtures are necessary.
Maximum near-field energy can be captured from a single or a
multiple number of small antennas while they are DC biased without
requiring a special fixture. RF signal and DC bias to the AUT are
applied through the probe station RF and DC probes. Multiple
measurements and characterizations can be accomplished in hours or
days instead of months as with conventional ranges. Thus, this
measurement capability significantly reduces time and costs
associated with antenna characterization, and allows for quick
optimization of prototype design concepts through measurement
validation.
[0037] The schematic of FIG. 2 shows a platen 30 on which an AUT 32
is mounted. A waveguide probe 34 is positioned above the AUT and is
for movement within the scan plane 36 in accordance with
instructions that are received from the VNA 38. The VNA receives
data from the AUT 32 and communicates with the CPU 40.
[0038] Turning next to FIG. 3, additional details of the hardware
of the present invention are shown. In particular, a DC probe 42 is
connected to the VNA 38 and provides a DC bias to any bias pads on
a transmitting AUT. The implementation of the present invention
requires a RF probe station, a coplanar waveguide
ground-signal-ground (G-S-G) microwave probe 44, and a scanning
probe 34 such as an open ended waveguide probe. The RF probe
station is available from sources such as Cascade Microtech, Inc,
Signatone Corporation and J micro Technology, Inc. G-S-G probes are
made by GGB Industries, Inc., The Micromanipulator Company, and
Lake Shore Cryotronics, Inc. Scanning probes such as waveguide
probes are available from sources such as Nearfield Systems, Inc,
Agilent Technologies, Inc and Maury Microwave Corporation. A
computer controlled 3-axis probe slide and probe rotation mechanism
provides 4 degrees of freedom for data acquisition at described
grid points of a near-field plane very close to the AUT and at
different polarizations. This mechanism comprises an X-axis
actuator 46, a Y-axis actuator 48, a Z-axis actuator 50, and a
rotator 52. A vector network analyzer/microwave receiver 38 (such
as a HP8510C) and a computer 40 complete the system. Software
controlled data analysis and visualization after each scan is
achieved through a GUI which displays the AUT's far-field radiated
pattern. Compared to prior art scanners, this near-field scanner
offers much faster antenna measurements at a fraction of the
cost.
[0039] The LabVIEW control panel is shown in FIG. 4 and consists of
a window to jog the probe, enter appropriate scan parameters, and
see initial test data which can be viewed and analyzed later
through the methods to be explained infra. The top section is used
for jogging the probe. The user can enter the desired linear
movement of the RF probe in millimeters, or the rotation in degrees
followed by clicking one of the eight movement buttons
corresponding to the four different axes to execute the movement.
When the probe is jogged to a new position, this position
automatically becomes the new Home position for the scanner. When
running a scan, the Home position preferably is directly above the
center of the intended scan area.
[0040] In certain circumstances the user may need to move the
probe, but may want to retain the current Home position. This can
be accomplished with the Freeze as Home button. When this button is
selected no jogging command can reset the Home position. When this
button is deselected the original Home position will still be
preserved until a jog is performed again. The probe can be returned
to the starting position at any time outside of performing a scan
by selecting the Home button.
[0041] The top section of the panel also includes a Microscope
button which is used to load an antenna onto the probe station's
platen. The waveguide probe must be moved out of the way to enable
the microscope to be loaded onto the bridge mount to aid in biasing
the antenna. When this button is pressed, the probe will be
positioned to the far right corner of the linear actuation range.
This movement will not cause the Home position to be reset.
Pressing the Home button will reposition the probe to the position
it was in before the Microscope button was selected. If the probe
had not been positioned prior to pressing the Microscope button,
then the Home position will not be defined by the user but by a
predefined location hard coded into LabVIEW.
[0042] The section of the control panel below the jog portion of
the panel is the parameter portion. This section is located on the
center of the LabVIEW panel. Here, the user must input all the
important parameters for the scan. The user should use caution when
establishing the number of data points and spacing to prevent
crashing the probe with any objects that may be in the scan area.
Every input must have an entry except for the Scan Comments text
box. This is an optional input that will allow the user to record
any important scan information to the Experiment_Parameters.rtf
file.
[0043] At the bottom of the control panel is the status portion of
the panel. Here, the user can monitor the progress of the scan,
stop the scan, or analyze the data after a scan is complete. When
the Stop button is selected the scan will be abruptly stopped at
the beginning of the next horizontal data point. If the program
requires scanning the area twice at 90-degree rotation shifts, then
data will be saved for the first shift if the Stop button is
selected after the first scan shift. Otherwise, no data will be
saved for that scan. The Graph & Analysis button will load a
new window to allow the user to view and analyze data from current
or previous scans, to be explained hereinafter.
[0044] For measurements, the AUT is first placed on the probe
station platform. An RF signal is then applied to the AUT feed
point through G-S-G probe, and DC bias to any bias pads on the AUT
is applied through a DC probe. The near-field scan area dimension
and the grid size resolution for probe data intake are user defined
in the control panel input. Probe slide hardware determines the
scan area and number of measurement points from the user input.
Once the probe is directed to move to the "home" position of the
scan box, the scan process is started with a button click. The RF
probe auto traverses on the scan area and captures the near-field
power distribution from AUT at the grid points. Automated data
storage and multiple window graphic display allows pattern
visualization capabilities in cross-sectional, 3-dimensional, and
contour formats for easy figure-of-merit comparison among design
variations and to quickly arrive at an optimized design.
[0045] Near-field data acquisition allows better power capturing
capabilities and therefore is very convenient to characterize
miniaturized antennas with low gain. This new capability allows
prototype antennas to be characterized, either of a single design,
multiple variants of one design, or multiple antenna designs on the
same substrate, in one session. FIG. 9 shows multiple antennas 32
a, b, c and d on a singular wafer 28, and mounted on a platen 30.
Four G-S-G probes 44 are also shown, each with a signal probe 64
contacting the AUT. The two grounds 56, 58 of each probe are joined
to pads 60, 62 on the platform 28 on which the antennas are
mounted.
[0046] Significant advantages of the present invention include 1)
fast, turn-key, automated, user-friendly system, 2) elimination of
wafer dicing or packaging of individual antenna before
characterization, 3) elimination of any test fixture or mounting
scheme with special connector, launcher, or feed line transition,
thereby reducing prototype optimization time and cost, 4) data
analysis and graphic visualization without requiring costly
stand-alone platforms, and 5) extensive pattern visualization
capability. The scanner system can be used for such programs as
exploration missions in which it can accelerate the development and
characterization of miniaturized antennas for lunar/planetary
surface to surface communications.
[0047] Several other advantages of the invention are a) the scanner
offers many versatile viewing and data comparison options; b) the
in plug-and-play mode features are unique with respect to other
known antenna test ranges; c) because miniaturized antennas are
required for many applications (e.g. surface networks and planetary
exploration communication), an effective, fast, and reliable
characterization capability can be very timely in maintaining
project timelines. Further, the technology can be used for
applications such as evaluation of miniaturized antennas for
cellular telephones, and embedded medical circuits.
[0048] The present invention can be implemented in accordance with
the following summary of the procedure for preparing and
calibrating the test equipment, conducting the test, and then
converting the near-field results into more useful far-field
data.
[0049] An S-parameter (e.g, S.sub.11) calibration is performed with
the VNA at the anticipated scanning frequency for the purpose of
defining the scattering parameters of the system. The frequency
range is limited by the VNA and the availability of the scanning
probe. The VNA is operational from 45 MHz to 40 GHz, and the probes
size will vary according the desired frequency, with the probe size
decreasing inversely to frequency. Therefore, in principle the
systems can be operational within the aforementioned range. This
calibration will help ensure the antenna is properly mounted and
ready for scanning before the test begins. In this example, the
scanner is run using the LabVIEW code.
[0050] The waveguide probe is moved into a corner of the linear
actuator so it does not interfere with a visual magnifier such as a
microscope that may be used for connecting the RF and DC probes to
the antenna. The AUT is placed onto the Probe Station's platen and
is maintained in position using suitable means such as a vacuum
system or other means that does not distort the AUT or alter its
power distribution properties. The RF probe is then placed on the
antenna's feed port followed by any DC probes that may be needed.
The S.sub.11 measurements are checked on the VNA to verify that the
antenna is properly biased.
[0051] After the antenna is successfully biased, the microscope is
removed and the microscope mounting bracket is returned to the far
back of the probe station to avoid contact with the probe during
operation. Removing the microscope and repositioning the bridge
mount may cause movement and vibrations in the probe station.
Accordingly, the S.sub.11 parameters are rechecked to assure the
antenna is still properly biased.
[0052] To prepare the scan, the waveguide probe is positioned
directly over the center of the AUT. There are two different
options for doing this. The user can either manually jog the probe
from the position at the corner of the linear actuator, or use a
Home button on the computer keyboard. If the probe has been moved
prior to centering, then it will return to this original position.
If the probe had not been moved prior to centering, then the Home
button will place the probe at a predefined location hard coded
into the computer program. Caution should be exercised when moving
the waveguide probe to prevent crashing it into the probe station.
The probe is then centered over the AUT, at the desired height and
rotation for conducting the desired tests before proceeding.
[0053] After the probe is prepared, the following test parameters
are keyed into the computer. These parameters include:
[0054] Frequency--The single frequency at which the AUT will
radiate (e.g., 2 GHz) The equipment involved in the scan
(waveguide, VNA, etc.) must be compatible with the set frequency
used in the scan.
[0055] Delay--The time delay the probe should pause at each data
position. The data are recorded 100 ms before the probe begins to
move again. So for a delay of 1s, the data are measured and
recorded 900 ms after stopping. If Delay is set to zero, a
continuous scan is conducted.
[0056] Averaging--The number of data points averaged by the VNA for
each recorded data point.
[0057] Ground Plane--Used in far-field calculations. Yes is chosen
if the AUT has a ground plane. Otherwise, N is selected.
[0058] Cal Set--Allows the user to load a predefined Cal Set saved
on the VNA. This Cal Set must be a CW calibration conducted
directly on the VNA and must coincide with the correct frequency
entered in the LabVIEW Panel. If the Cal Set differs from the
frequency being tested or is not CW, it will be ignored by the
scanner.
[0059] Polarization--Allows polarization of the AUT to be chosen.
This determines the type of data that will be saved and how
calculations are done for the far field conversion.
[0060] FE Resolution--Used to determine the number of data points
to be used in the far-field conversion. Standard creates a
far-field matrix of 128.times.128, High creates a matrix of
256.times.256, and Very High creates a matrix of 512.times.512.
[0061] X axis Data Points--The number of data points along the
x-direction that should be recorded during scanning. This number is
typically an integer value.
[0062] Y axis Data Points--The number of data points along the
y-direction that should be recorded during scanning. This number
should be an integer value.
[0063] X axis Data Intervals--The interval spacing between x data
points in units of millimeters. This number can be a decimal value
to the hundredths position.
[0064] Y axis Data Intervals--The interval spacing between y data
points in units of millimeters. This number can be a decimal value
to the hundredths position.
[0065] Scan Comments--This text box allows the entry of any
comments about the scan to be saved in the parameter text file.
[0066] Filepath--The file path of the data being saved. This data
path must specify a folder in memory.
[0067] Filename--The File name of the data being saved. This
Filename creates a folder that contains all the files created from
the scan. The folder will have the unique name for the scan,
however, the files inside the folder will be uniform across other
scans.
[0068] When the test apparatus is properly set up, the scan begins
by pressing the Scan button. The probe positions itself over the
Home position. It then proceeds to position itself at the location
of the first data point. All scan lines are conducted across the
x-axis. The status bar gives an estimate of the progress for the
scan.
[0069] When the scan is complete, the data is displayed in three
graphs shown as FIGS. 5, 6 and 7. The Figures are shown in color to
more accurately display the various slopes and contours portrayed
in the graphs. The graphs are generally located on the right side
of the LabVIEW panel. The Near-Field phase and magnitude are
typically displayed in the two small graphs, FIG. 5 and FIG. 6
respectively, shown on the monitor, while the Far-Field pattern is
displayed in the larger graph (FIG. 7). Depending on the
polarization type, the scan may need to be conducted twice at 90
degree rotation shifts. If two scans are required, the graphs will
be updated twice. After the first scan the near field magnitude and
phase are displayed in the two smaller graphs. If the scan is
"CoPol and CrossPol" then the Co-Pol far-field is also be displayed
for the first scan. If the scan is circular no far-field pattern
will be displayed. After the second scan, the new near-field
magnitude and phase are then displayed along with either the
circular far-field or updated Co-Pol far field dependent on the
type of polarization that is chosen. For more graphing features, a
"Graph & Analysis" button located in the status portion at the
bottom of the LabVIEW panel can be used.
[0070] The "Graph & Analysis" button opens a screen allowing
the user to choose the desired data folder. When a data folder is
chosen, a display shows a list of different graphs available based
upon the polarization of the scan within the data folder. The user
may choose as many of the graphs to display before clicking the
Open button. Each graph opens in its own separate window. This
allows as many graphs to be viewed as required. The graphs can be
resized by maximizing or dragging the window edges. The 2D graphs
representing the H-cut and V-cut allow the user zoom in on a region
of the graph. Double clicking on the graph will return the graph to
its original state. Future graphs can be opened from the File menu
on each graph window. Each graph has the ability to be saved as a
bitmap file in the folder containing the scan data for later use.
This is accomplished by clicking on Save as Image in the File menu.
Each graph can also be printed from the File menu. The printed size
is determined by the size the graph appears on the monitor. A full
page printout can be obtained by maximizing the graph window and
choosing Print.
The Data Files
[0071] After each scan, a number of data files are saved to the
scan folder. These files are matrices delimited by a tab and can
easily be accessed using a computer program such as Excel. The scan
polarization determines the number and type of files saved in each
scan folder. Each scan will contain certain files. Those files
include: [0072] Graph_Parameters.gd--This is information needed for
the graphing feature. If this file is removed or altered the
graphing features in LabVIEW may not work. [0073] Experiment
Parameters.rtf--This is a text file saved in the "Rich Text File"
format. This file will display all the parameters used when the
scan was conducted along with any user comments entered in the
"comment box" before the scan. [0074] theta.psd--The theta values
corresponding to each far field data point. [0075] phi.psd--The phi
values corresponding to each far field data point. [0076]
u.psd--The u values corresponding to each far field data point.
[0077] v.psd--The v values corresponding to each far field data
point.
[0078] Finally, the LabVIEW program generates the three graphs as
shown in FIGS. 5, 6 and 7. The two near field graphs, FIGS. 5 and
6, are constantly updated while data is being taken so the user can
monitor the progress and state of the data recorded thus far. For
"CoPol & CrossPol" scans, the far field pattern shown in FIG. 7
is updated after each scan shift displaying the Co-Pol far field
pattern each time. For circularly polarized scans the far field
display will only be updated after the second scan shift.
[0079] After a scan is complete, all the appropriate data are saved
in the folder named by the user from the LabVIEW Panel. If the
folder already exists, the user will be prompted to enter a new
folder name before data can be saved. All data files are saved in
matrix form with each horizontal data point delimited by a tab.
This allows the data to be read easily into a spreadsheet.
[0080] Obviously, the relative sizes and locations of these panels
in the window is arbitrary and can be changed in accordance with
the needs and the preferences of the user.
[0081] A more detailed analysis can be made of the graphs shown in
FIGS. 5, 6, 7 and 8 from the Graph & Analysis button located at
the bottom of the LabVIEW Panel shown in FIG. 4. This option
displays a menu for the user to choose which folder contains the
data. When a properly formatted folder is chosen, the menu reads
the polarity of the data from the contents of the folder and
displays a list of graphs available for viewing. The number of
different data files for plotting range from three to six,
depending on the scan polarity. For example, a "CoPol Only" scan
will contain the near field magnitude, near field phase, and far
field data matrices for plotting. However a "CoPol & CrossPol"
will contain both magnitude and phase for each near-field scan and
a Co-Pol far-field pattern along with a Cross-Pol far-field
pattern. The software determines the polarity that the data folder
contains and only allows the user to choose graphs appropriate for
that scan.
[0082] When a data folder is chosen, a variety of graphs can be
selected for viewing. Each data file can be viewed in four
different formats. These formats are 3D, H-Cut, V-Cut, and Contour.
The 3D graph option shows the data in 3 dimensional space allowing
the graph to be rotated for viewing it at different angles. The
H-Cut will show the horizontal cut of the data with respect to the
probe station beginning from left to right, whereas, the V-Cut will
show the vertical cut of the data with respect to the probe station
from top to bottom. Finally, the contour will display the magnitude
of the data as if it were viewed directly from above the probe
station. It is displayed through shadowing where lighter shades
represent a higher value and darker shades represent lower
values.
[0083] Each of the 3D graphs viewed in FIGS. 5, 6 & 7 is given
a folder name and graph type displayed in the caption of the window
as well as being displayed above the graph. Each graph also
contains a series of menus depending on the type of graph being
displayed.
[0084] Every graph contains a File menu. Inside the File menu are
four options. These options are Open, Save as Image, Print, and
Close.
[0085] The Open option will redisplay the graph menu and allows the
user to open any new graphs they choose.
[0086] The Save as Image option will save the current screen shot
of the graph to a bitmap image in the corresponding data folder for
that graph.
[0087] The Print option writes the graph to a printer.
[0088] Finally, the Close option exits out of that single graph
window. Each graph contains a Graph menu. Depending on the data
being displayed and graph type, the Graph menu includes different
options. Each Graph menu, however, will at least contain the Add
Cursor option. When selected, a cursor will be added to the graph
at the maximum value which can be dragged around to different data
points on the graph. The graph title will also change to include
the coordinates of the cursor.
[0089] For data other than near field phase, the user has the
option to find the peak of the graph. This can be done by selecting
Find Peak in the Graphs menu. When this is chosen the cursor is
moved to the graph's peak and the position is reflected in the
graph's title.
[0090] Contour graphs of the type shown in FIG. 8 contain
additional features from the other three graph types. The contour
graph can display both the surface in shades representing different
point values and also in the form of contour lines. In the Graph
menu the user can choose See Contour Levels and the graph will be
transformed from surface shading to contour lines. When the graph
is in the contour line display, the menu option will change to See
Contour Surface and can be transformed back to the surface plot
through this new option. The data represented by the graph will
dictate the spacing of these contour lines. If these contour lines
are too crowded or not sufficient, the user can add and remove
contour lines as needed. When the graph is in Contour-Level mode,
two new options are displayed in the Graphs menu. These are Add
Contour Level and Remove Contour Level.
[0091] For far-field patterns, the -3 dB contour line is displayed
in red. From the Add Contour Level menu option, contour lines of
any value (to the tenths decimal position) can be added to the
graph in any color chosen by the user.
[0092] The user can enter the contour level to add to the graph
along with adjusting the color of the contour level by sliding the
scroll bars on the right corresponding to the colors red, green,
and blue. The color box indicates the current color chosen by the
user. The screen defaults at black which is when all three scroll
bars are positioned to the far left. By scrolling the color bars to
the right, the color of the contour level will contain more of that
corresponding color. For example, for a green contour level, the
red and blue scroll bars should remain to the far left while the
green scroll bar is slid to the far right. Along with adding new
contour levels a user can remove any existing contour levels
[0093] Each existing contour level is listed in a drop-down menu.
The user should select the contour level to be removed and click
OK. Only one contour level can be removed at a time, but there's no
limit to how many contour levels must be displayed on a graph.
[0094] Another option in the Graph menu is the Remove Grid option
When grid lines are removed for better visibility, this option will
be changed to Restore Grid, so the user has the option to restore
the grid lines back onto the graph.
[0095] The cursor option can be used in both the surface and
contour parts of the contour display. When switching between
surface and contour lines, the cursor will be removed and the user
can add the cursor again to continue using it. The cursor will not
necessarily be added in the same spot it was before the graph
transitioned from surface to contour lines or vice versa.
Far-Field Graphs
[0096] Far-field graphs differ from the near-field graphs in
several ways. First, all the near-field graphs contain the same
size data matrix. However, far-field data matrix sizes are defined
by the FF Resolution and the MATLAB transformation of the
near-field data to far-field data. The FF Resolution input on the
LabVIEW panel allows the user to decide on the size of the matrices
to use in the far-field transformation. The near-field data will
consist of part of this matrix padded with 0s everywhere else. When
the transformation occurs, the entire matrix is analyzed and
unrealistic data is removed. In this case, unrealistic data would
be data points where theta exceeds 90 degrees. These two factors
determine the size of the far-field data matrix. Another difference
between far-field plots and near field plots are the x-, and
y-axes. In near-field graphs these axes are defined by the physical
space scanned above the antenna. In far-field graphs there are two
possible displays. The default display is in theta-phi space. Phi
and theta are spherical coordinates attempting to be displayed on a
Cartesian graph. This is accomplished by visualizing from above,
the hemisphere that makes up the phi-theta plot. Phi remains the
same starting at 0 degrees pointing directly right from the center
of the plot and theta is displayed as the radius from the center of
the graph. This can be visualized by imagining a hemisphere laying
flat on a plane. The phi-theta combinations that lie along the
hemisphere will be pulled directly down onto the plane below the
hemisphere. The z-axis represents the normalized power in dB at
each phi-theta point on the plane. This representation causes the
graph to take on a circular form limited by the fact that theta
(the radius) cannot be larger than 90 degrees.
[0097] The other coordinate system that far-field graphs can be
displayed in is U-V space. All far-field graphs have an extra menu
option called Convert to UV Space found in the UV-TP Space menu,
unique to far-field graphs. This transforms the graph from
theta-phi space to U-V space. While the graph is in U-V space, the
menu option becomes Convert to TP Space which allows the graph to
be transformed back to theta-phi space. U-V space is an imaginary
space used in the calculation of near-field data to far-field data
and is familiar to those in the antenna pattern discipline. All the
other graph features can be run in U-V space in the same manner as
in the theta-phi space.
Raw Data vs. Graphed Data
[0098] The coordinate system for transforming near-field data to
far-field data uses the upper-left point as the origin with the
x-axis pointing down and the y-axis pointing across. Therefore, a
far-field transformation of these data will display the data as if
viewed at a 90 degree clockwise shift from the direction the data
are scanned. However, to keep the data display as simple as
possible, this software rotates the data back to the same
orientation being scanned on the probe station. This is important
if raw far-field data are to be used later.
[0099] Each scan folder contains these files: [0100]
Graph_Parameters.gd--This is information needed for the graphing
feature. If this file is removed or altered, the graphing features
in LabVIEW may not work. [0101] Experiment Parameters.rtf--This is
a text files saved in the "Rich Text File" format. This file
displays all the parameters used when the scan was conducted, along
with any user comments entered in the "comment box" before the
scan, [0102] theta.psd--The theta values corresponding to each
far-field data point. [0103] phi.psd--The phi values corresponding
to each far-field data point. [0104] u.psd--The u values
corresponding to each far-field data point. [0105] v.psd--The v
values corresponding to each far-field data point.
[0106] The different polarization files are described below: [0107]
CoPol Only--CoPol_Magnitude.psd--The Near-Field Magnitude of the
Co-Pol Scan. [0108] CoPol_Phase.psd--The Near-Field Phase of the
Co-Pol Scan. [0109] CoPol.psd--The Co-Pol Far-Field Pattern. [0110]
CoPol_Real_Data.psd--The real data of the Co-Pol Scan. [0111]
CoPol_Imaginary_Data.psd--The imaginary data of the Co-Pol Scan.
[0112] CrossPol Only--CrossPol_Magnitude.psd--The Near-Field
Magnitude of the Cross-Pol Scan. [0113] CrossPol_Phase.psd--The
Near-Field Phase of the Cross-Pol Scan. [0114] CrossPol.psd--The
Cross-Pol Far-Field Pattern. [0115] CrossPol_Real_Data.psd--The
real data of the Cross-Pol Scan. [0116]
CrossPol_Imaginary_Data.psd--The imaginary data of the Cross-Pot
Scan. [0117] CoPol & CrossPol--CoPol_Magnitude.psd--The
Near-Field Magnitude of the Co-Pol Scan. [0118]
CoPol_Phase.psd--The Near-Field Phase of the Co-Pol Scan. [0119]
CoPol.psd--The Co-Pol Far-Field Pattern. [0120]
CoPol_Real_Data.psd--The real data of the Co-Pol Scan. [0121]
CoPol_Imaginary_Data.psd--The imaginary data of the Co-Pol Scan.
[0122] CrossPol_Magnitude.psd--The Near-Field Magnitude of the
Cross-Pol Scan. [0123] CrossPol_Phase.psd--The Near-Field Phase of
the Cross-Pol Scan. [0124] CrossPol.psd--The Cross-Pot Far Field
Pattern. [0125] CrossPol_Real_Data.psd--The real data of the
Cross-Pot Scan. [0126] CrossPol_Imaginary_Data.psd--The imaginary
data of the Cross-Pol Scan. [0127] LH
Circular--x_Magnitude.psd--The Near-Field Magnitude of the x scan.
[0128] x_Phase.psd--The Near-Field Phase of the x scan, [0129]
x_Real_Data.psd--The real data of the x Scan. [0130]
x_Imaginary_Data.psd--The imaginary data of the x Scan, [0131]
y_Magnitude.psd--The Near-Field Magnitude of the y scan. [0132]
y_Phase.psd--The Near-Field Phase of the y scan. [0133]
y_Real_Data.psd--The real data of the y Scan. [0134]
y_Imaginary_Data.psd--The imaginary data of the y Scan. [0135]
LH_Circullar.psd--The LH Circular Far-Field pattern. [0136] RH
Circular--x_Magnitude.psd--The Near-Field Magnitude of the x scan.
[0137] x_Phase.psd--The Near-Field Phase of the x scan, [0138]
x_Real_Data.psd--The real data of the x Scan. [0139]
x_Imaginary_Data.psd--The imaginary data of the x Scan. [0140]
y_Magnitude.psd--The Near-Field Magnitude of the y scan. [0141]
y_Phase.psd--The Near-Field Phase of the y scan. [0142]
y_Real_Data.psd--The real data of the y Scan. [0143]
y_Imaginary_Data.psd--The imaginary data of the y Scan. [0144]
RH_Circular.psd--The RH Circular Far-Field pattern.
[0145] The near-field to far-field transformation is implemented by
the probe station near-field scanner.
##STR00001##
Assuming that the probe is a perfect linear antenna, the total
aperture field measured by the probe can be represented in the
coordinate system shown above as follows:
.sub.a(x,y)=E.sub.ax(x,y) .sub.x+E.sub.ay(x,y) .sub.y (1)
where, E.sub.ax(x,y) the complex field measured with the probe
oriented in the .sub.x direction and E.sub.ay(x,y) the field
measured with the probe .sub.y directed. This expression is valid
for any antenna, regardless of orientation or polarization,
inasmuch as the total vector field is simply resolved into two
orthogonal components. Obviously if a single scan is used to obtain
aperture field data, the field of the orthogonal polarization is
assumed to be zero.
[0146] Using the magnetic field equivalence principle, the far zone
radiation field of this aperture field can be expressed as:
(.theta.,.phi.)=E.sub..theta.(.theta.,.phi.)
.sub..theta.+E.sub..phi.(.theta.,.phi.) .sub..phi. (2)
with
E .theta. = j.beta. 4 .pi. [ P x cos ( .phi. ) + P y sin ( .phi. )
] ( 3 ) E .phi. = j.beta. 4 .pi. cos ( .theta. ) [ P y cos ( .phi.
) + P x sin ( .phi. ) ] . ( 4 ) ##EQU00001##
The terms,
P.sub.x(u,v)=.intg..sub.s.intg.E.sub.ax(x',y')e.sup.jw'e.sup.jw'dx'dy'
(5)
P.sub.y(u,v)=.intg..sub.s.intg.E.sub.ay(x',y')e.sup.jw'e.sup.jw'dx'dy'
(6)
are Fourier Transform integrals in the variables,
u=.beta. sin(.theta.)cos(.phi.) (7)
v=.beta. sin(.theta.)sin(.phi.) (8)
with
.beta. = 2 .pi. .lamda. . ##EQU00002##
The integration is performed over the surface S, which is defined
by the limits of the scan plane. These integrations are the basis
of the near-field to far-field transformation. Note, in this
application, the integrations of Equations (6) and (7) are
performed with the two dimensional Fast Fourier Transform (FFT)
routine provided in MATLAB. The FFT requires that the number of
sample points be a power of 2. Since, in general, the number of
data points from the test will not be a power of 2, the data set is
augmented by zeros to meet the FFT criteria. In addition to
providing the increased computational speed of the FFT,
augmentation increases the resolution of the function in the
transform domain. The probe station software utilizes this property
by allowing the user to set the resolution of the far-field pattern
in the setup screen. Effectively, when a resolution is selected,
the total number of points used in the FFT is chosen.
[0147] The Fourier Transform relationship is obtained through the
variable substitutions defined in Equations (7) and (8). Thus the
aperture field is transformed by Equations (5) and (6) to a space
defined by the range of (u,v). The transformation can be visualized
in this space and this option is provided by the Probe Station
Near-Field Scanner Software.
[0148] The (u,v) space results from mathematical convenience and
has to be converted to (.theta.,.phi.) in order to visualize the
field in real space. When converting to (.theta.,.phi.), points
where
.theta. > .pi. 2 ##EQU00003##
are disregarded. This limitation is imposed by the magnetic
equivalence theorem which assumes the aperture field exists in an
infinite plane and does not radiate in the region where z<0. The
Probe Station Near-Field Scanner Software provides a number of
graphing options to visualize the field in (.theta.,.phi.)
space.
[0149] The form of the far-field electric field, shown in Equations
(3) and (4), is appropriate for apertures in a conducting ground
plane. For apertures in free space, the field is more accurately
given by A. Ludwig, "The Definition of Cross Polarization", IEEE
AP-S January 1973, pp 116-119.
E .theta. = j.beta. 4 .pi. 1 + cos ( .theta. ) 2 [ P x cos ( .phi.
) + P y sin ( .phi. ) ] ( 9 ) E .phi. = j.beta. 4 .pi. 1 + cos (
.theta. ) 2 [ P y cos ( .phi. ) + P x sin ( .phi. ) ] . ( 10 )
##EQU00004##
In general, any component of the far-field can be displayed by
using the equation,
E.sub.display(.theta.,.phi.)= E(.theta.,.phi.) .sub.d (11)
where .sub.d is a unit vector in the direction of the desired
component. In the most general sense, the user can be allowed to
choose the component of the field however the software provides the
most commonly used components. For example, to display the
{circumflex over (.theta.)} component, .sub.d= .sub..theta. is used
in Equation (11).
[0150] The co-polarized field and the cross-polarized field are
computed following the third definition provided by Ludwig (supra).
This definition states that the reference direction of the
polarization (Co-Pol) is that direction a far-field probe must
match at .theta.=0 in order to receive maximum power. For the
Co-Pol pattern, this probe must match and maintain the relationship
with {circumflex over (.theta.)} and {circumflex over (.phi.)} at
all angles. Similarly, Cross-Pol pattern is obtained by using a
unit vector orthogonal to the Co-Pol vector.
[0151] For a linearly polarized AUT, the co-pot direction depends
on the orientation of the AUT. So for an AUT with a polarization
angle that is oriented at an angle .beta. to the {circumflex over
(x)} axis,
.sub.d= .sub.co=cos(.phi.-.beta.) .sub..theta.-sin(.phi.-.beta.)
.sub..phi. (12)
and
.sub.d= .sub.cross=sin(.phi.-.beta.)
.sub..theta.-cos(.phi.-.beta.)i.sub..phi.. (13)
Because the probe that is used with the Probe Station Scanner is a
linearly polarized waveguide, a circularly polarized AUT requires
two scans. The second scan must be done with the probe rotated
90.degree. from the first. The right hand and left hand polarized
components of the field are constructed from using the unit
vectors
i ^ d = i ^ rh * = 1 2 ( i ^ x - j i ^ y ) * , ( 14 ) and i ^ d = i
^ lh * = 1 2 ( i ^ x - j i ^ y ) * . ( 15 ) ##EQU00005##
The conjugate is used because the field to be shown would be the
field received by an ideal circularly polarized antenna located at
the far-field point. Note that to actually perform the dot product
with these vectors, the far-field has to be transformed to a
rectangular coordinate system.
[0152] Finally, co-polarized and cross-polarized fields for
circular polarization can be determined through the use of the unit
vectors,
i ^ d = i ^ co = 1 2 { [ cos ( .phi. ) + - j.delta. sin ( .phi. ) ]
i ^ .theta. - [ sin ( .phi. ) - - j.delta. cos ( .phi. ) ] i ^
.phi. } ( 16 ) i ^ d = i ^ cross = 1 2 { [ cos ( .phi. ) - -
j.delta. sin ( .phi. ) ] i ^ .theta. - [ sin ( .phi. ) + - j.delta.
cos ( .phi. ) ] i ^ .phi. } . ( 17 ) ##EQU00006##
The sense of the polarization is selected using
.delta.=.pi./2 Left Handed Circular Polarization, and
.delta.=-.pi./2 Right Handed Circular Polarization.
[0153] While the invention has been described in combination with
specific embodiments thereof, there are many alternatives,
modifications, and variations that are likewise deemed to be within
the scope thereof. Accordingly, the invention is intended to
embrace all such alternatives, modifications and variations as fall
within the spirit and scope of the appended claims.
* * * * *