The Expert MININEC Series modeling process has five principal steps. These steps are:
The specific options available are dependent on the specific computer program of the Expert MININEC Series. The specifics of the individual programs are available:
One of the classic problems in antennas is the analysis of dipole antennas. Consider two parallel one-half meter dipoles of radius .001 meters. The two dipoles are 0.1 meters apart. First, the points of the geometry must be defined. The two dipoles are defined by the end points of each of the two wires. In Cartesian coordinates and the dipoles centered about the origin the two geometry points for the first wire are (-.05, 0, -.25) and (-.05, 0, .25). The two geometry points for the second wire are (.05, 0, -.25) and (.05, 0, .25).
These geometry points are defined by appropriately filling the Geometry points dialog box. The environment is free space, and a Cartesian coordinate system is defined. In this dialog box there are several push buttons. These push buttons are common to a general dialog box. The following describe the actions of these common push buttons:
OK - accept all of the user inputs and close the dialog box.
Apply - accept all of the user inputs, but do not close the dialog box.
Reset - ignore all of the user inputs since the dialog box appeared or since the user last hit the Apply button (whichever happened last), but do not close the dialog box.
Cancel - ignore all of the user inputs since the dialog box appeared or since the user hit the Apply button (whichever happened last), but close the dialog box.
Using {ALT} with the underlined letter of the word designating the push button will depress the button. At the top of many dialog boxes is a list box which contains a list of the defined parameters. This list box has several features. The number of the highlighted entry and the total number of entries are displayed on top of list box. Clicking with the left mouse button on an entry in the list box fills the text boxes with the parameter data for that entry. Additional push buttons are:
Add - adds parameters in text boxes to list box.
Modify - modifies the highlighted entries with the current entries in the text boxes.
Delete - deletes the current highlighted entries in the list box.
Shift + Click or Ahift + Arrow key extends the selection from the previously selected entry to the current entry. {CTRL} + click selects or deselects an entry from the list. {ALT}L selects all entries in the list box.
Several different coordinate systems are available in the Geometry points dialog box. If the coordinate system is Cartesian, the location of the geometry point is (X, Y, Z). If the coordinate system is cylindrical, the location of the geometry point is (Radius, Angle, Z), where the angle is the azimuthal angle from the X axis. If the coordinate system is geographic, the location of the geometry point is (Distance, Angle, Z). Distance is the distance from the origin. Angle is measured from true North toward the East. The translation to the Cartesian system assumes that the X axis is oriented toward true North. The Cartesian coordinates are rotated ninety degrees clockwise from, and are the mirror image of the geographic system.
There are several intrinsic diagnostics that are inherent in the Geometry points dialog box. The inputs are checked such that
Duplicate geometry points are not allowed.
If a ground condition is specified for the environment, values for Z less than zero are not accepted. All ground planes are infinite in extent. If a perfect ground is defined, the current calculations are made with image theory. If a real ground is defined, the Reflection Coefficient Approximation is used.
The next step is to define the attributes of each wire. This includes the geometry points of each end of the wire, the number of segments, radius and end cap options. This is accomplished by filling the Straight wires dialog box. For this example, end caps were not used. Wires are defined only by geometry points of the ends of the wires. The intersection of two wires at a point not at the ends of both wires does not result in a connection. Wires are connected only when an end of both wires have the same geometry point. If a ground plane is used, a wire is connected to ground if one of its geometry points has the Z coordinate equal to zero.
There are several intrinsic diagnostics that are inherent in the Straight wires dialog box. The inputs are checked such that
Coincident wires are not allowed.
Radius must be greater than zero. The default is .001.
The geometry point is an integer that cannot be greater than the number of nodes. The number of points is equal to the number of entries in Geometry points dialog box. The default is the number of points.
End caps are not allowed to be part of a junction. Straight wires removes the end cap request appropriately. Selecting the End caps option will add the radius of the wire to the length of the wire on the specified end.
Each wire is divided into segments for analysis purposes. For this example, each dipole has six segments. The validity of the computation is critically dependent on the choice of the number of segments. Although accuracy improves with an increase in the number of segments, both the computational time and memory also increase. It is part of the modeling art that the user choose a segmentation scheme that is sufficiently accurate within the allowable computation time and memory requirements. Depending on the complexity of the problem, segment lengths on the order of .02 wavelengths are suggested. The electrical frequency of the computation is required in order to make a determination of the segment length in wavelengths.
The location of current nodes is dependent on the number of segments. The location of the current nodes for the parallel dipole example are given in the following table.
CURRENT NODEScoordinates (meters) connections node wire X Y Z end1 end2 no. 1 -.05 0 -.1666667 END 1 1 1 -.05 0 -.08333333 1 1 2 1 -.05 0 0 1 1 3 1 -.05 0 .08333334 1 1 4 1 -.05 0 .1666667 1 END 5 2 .05 0 -.1666667 END 2 6 2 .05 0 -.08333333 2 2 7 2 .05 0 0 2 2 8 2 .05 0 .08333334 2 2 9 2 .05 0 .1666667 2 END 10
The list of current nodes is explained by understanding the segmentation of a wire and the expansion of currents about the segments. A wire is subdivided into segments, and the current is expanded as triangles centered at adjacent segment junctions. The end points of a wire have no triangles. If a second wire is added to the model, the second wire is subdivided into segments with currents expanded as triangles as in the case of the first wire. In addition, if the second wire is attached to the first wire, a triangle is automatically located at the attachment end. Half of the additional triangle extends onto wire two, and half onto wire one. The half of the triangle on wire one assumes the dimensions (length and radius of the half segment of wire one), while the half of the triangle on wire two assumes the dimensions of wire two. Wire two overlaps onto wire one with a current triangle at the junction end. Additional wires may also overlap onto wire one. It can be shown that for a junction of N wires, only (N - 1) overlaps with associated currents are required to satisfy Kirchhoff's current law. The convention in the Expert MININEC Series is that the overlap occurs onto the earliest wire specified at a junction. A wire junction is established whenever the user defined coordinates of a wire end are identical to the end coordinates of a wire previously specified.
Next, consider a more complicated antenna with connecting wires. The dual quad antenna, a favorite of Ham radio enthusiasts, is used as the example. Eight geometry points are required to define eight wires. The required dialog boxes for Geometry points and Straight wires are displayed. The geometry summary for this problem definition is given in following table.
GEOMETRY
Dimensions in feet
Environment: FREE SPACE
wire caps X Y Z radius segs
1 none -5. -6.083 -6.083 .0033666 6
-5. 6.083 -6.083
2 none -5. 6.083 -6.083 .0033666 6
-5. 6.083 6.083
3 none -5. 6.083 6.083 .0033666 6
-5. -6.083 6.083
4 none -5. -6.083 6.083 .0033666 6
-5. -6.083 -6.083
5 none 5. -5.917 -5.917 .0033666 6
5. 5.917 -5.917
6 none 5. 5.917 -5.917 .0033666 6
5. 5.917 5.917
7 none 5. 5.917 5.917 .0033666 6
5. -5.917 5.917
8 none 5. -5.917 5.917 .0033666 6
5. -5.917 -5.917
The current nodes for the dual quad are given in the table below. Note the designation of the connections. For example, current node six is the connection point between wire 1 and wire 2 of the first quad (i.e., the additional overlapping triangle is located at node 6).
CURRENT NODES
coordinates (feet) connections node
wire X Y Z end1 end2 no.
1 -5. -4.055 -6.083 END 1 1
1 -5. -2.028 -6.083 1 1 2
1 -5. 0 -6.083 1 1 3
1 -5. 2.028 -6.083 1 1 4
1 -5. 4.055 -6.083 1 END 5
2 -5. 6.083 -6.083 1 2 6
2 -5. 6.083 -4.055 2 2 7
2 -5. 6.083 -2.028 2 2 8
2 -5. 6.083 0 2 2 9
2 -5. 6.083 2.028 2 2 10
2 -5. 6.083 4.055 2 END 11
3 -5. 6.083 6.083 2 3 12
3 -5. 4.055 6.083 3 3 13
3 -5. 2.028 6.083 3 3 14
3 -5. 0 6.083 3 3 15
3 -5. -2.028 6.083 3 3 16
3 -5. -4.055 6.083 3 END 17
4 -5. -6.083 6.083 3 4 18
4 -5. -6.083 4.055 4 4 19
4 -5. -6.083 2.028 4 4 20
4 -5. -6.083 0 4 4 21
4 -5. -6.083 -2.028 4 4 22
4 -5. -6.083 -4.055 4 4 23
4 -5. -6.083 -6.083 4 1 24
5 5. -3.945 -5.917 END 5 25
5 5. -1.972 -5.917 5 5 26
5 5. 0 -5.917 5 5 27
5 5. 1.972 -5.917 5 5 28
5 5. 3.945 -5.917 5 END 29
6 5. 5.917 -5.917 5 6 30
6 5. 5.917 -3.945 6 6 31
6 5. 5.917 -1.972 6 6 32
6 5. 5.917 0 6 6 33
6 5. 5.917 1.972 6 6 34
6 5. 5.917 3.945 6 END 35
7 5. 5.917 5.917 6 7 36
7 5. 3.945 5.917 7 7 37
7 5. 1.972 5.917 7 7 38
7 5. 0 5.917 7 7 39
7 5. -1.972 5.917 7 7 40
7 5. -3.945 5.917 7 END 41
8 5. -5.917 5.917 7 8 42
8 5. -5.917 3.945 8 8 43
8 5. -5.917 1.972 8 8 44
8 5. -5.917 0 8 8 45
8 5. -5.917 -1.972 8 8 46
8 5. -5.917 -3.945 8 8 47
8 5. -5.917 -5.917 8 5 48
A final example of geometry description considers an antenna connected to a ground plane. This example is a "TEE" antenna on a ground plane. The height is .04 meters. Both arms have lengths of .12 meters and radii of .002 meters. The radius of the vertical element is .001 meters. The vertical element has two segments, and each arm has six segments. The antenna is fed at the base. The dialog boxes for Geometry points and Straight wires are displayed. In the Geometry points a perfect ground is chosen for the environment. The current nodes for this TEE antenna geometry are given in the table below. Note the identification of ground as one of the connections for current node one.
CURRENT NODES
coordinates (meters) connections node
wire X Y Z end1 end2 no.
1 0 0 0 GND 1 1
1 0 0 .02 1 END 2
2 0 0 .04 1 2 3
2 -.02 0 .04 2 2 4
2 -.04 0 .04 2 2 5
2 -.06 0 .04 2 2 6
2 -.08 0 .04 2 2 7
2 -.1 0 .04 2 END 8
3 0 0 .04 1 3 9
3 .02 0 .04 3 3 10
3 .04 0 .04 3 3 11
3 .06 0 .04 3 3 12
3 .08 0 .04 3 3 13
3 .1 0 .04 3 END 14
The Expert MININEC Series includes modeling constructs beyond Geometry points and Straight wires that aid in the development of complex models. These constructs include helix, arc and circular wires. Wire meshes for the modeling of surfaces can also be generated using the Wire Mesh option. The Transformations option can move existing wires by rotation and translation. Copies of parts of the model can be generated. Partial symmetry can be used to reduce the time of calculation. Partial symmetry is efficient for the modeling of structures that have one nonsymmetrical case on the z-axis, such as in the case for the TEE antenna.
Once the geometry has been described, the electrical description must be defined. First, the frequency may be specified. In many cases a frequency is chosen such that the dimensions in meters are the same as the dimensions in wavelengths. In the Expert MININEC Series the frequency of 299.8 MHz has a wavelength of one meter. This frequency is selected by filling the Frequency dialog box appropriately. The units are in megahertz (MHz).
In order to calculate the currents and impedance, a source must be defined. For the example of the parallel dipoles, the first dipole is to be center fed with a voltage source of magnitude one volt with zero phase. Sources are defined in terms of the current nodes that result from the segmentation of the wires. Using the current nodes for the parallel dipoles example, the center node for the first dipole is current node 3. The desired voltage source is specified by filling the Voltage/current sources dialog box.
Sources are defined such that the positive terminal, the terminal of the direction of current flow, is in the direction of end two of the wire. If a wire is reversed, the polarity of the source will be reversed. A source placed at a junction of two wires is defined by the higher numbered wire. The positive terminal of the source is in the direction of end two of the higher numbered wire. For complex antenna structures the source direction should always be of concern. Especially, when multiple sources are used, the resulting currents should be evaluated in terms of the sources being defined in the correct directions.
The effect of a load at the center of the second dipole of (50, 0) can also be determined using the Lumped loads option. This load is specified at node 8 for the center node of the second wire. This loading option is specified by filling the Lumped loads dialog box.
There are four different options for checking the validity of a given model. These methods include
Definition summary
Definition evaluation
List of current nodes
3D display
Convergence test
The first option is the most straightforward. The Expert MININEC Series provides a summary of the problem description. As an example, the definition summary for the parallel dipoles problem is given in the table below. This description does not include the lumped load at current node 8. Careful review of the definition summary will determine if the geometry and electrical parameters have been correctly defined.
GEOMETRY
Dimensions in meters
Environment: FREE SPACE
wire caps X Y Z radius segs
1 none -.05 0 -.25 .001 6
-.05 0 .25
2 none .05 0 -.25 .001 6
.05 0 .25
Number of wires = 2
current nodes = 10
minimum maximum
Individual wires wire value wire value
segment length 1 .08333334 1 .08333334
segment/radius ratio 1 83.33333 1 83.33333
radius 1 .001 1 .001
ELECTRICAL DESCRIPTION
Frequencies (MHz)
frequency no. of segment length (wavelengths)
no. lowest step steps minimum maximum
1 299.8 0 1 .08333334 .08333334
Sources
source node sector magnitude phase type
1 3 1 1. 0 voltage
Definition evaluation is also available as an option under the Diagnostics option. Definition evaluation evaluates the problem definition against the Geometry guidelines:
For individual wires a check against the Geometry guidelines indicates the wire number, the type of violation, and the magnitude of the violation.
For junctions the check against the Geometry guidelines indicates the node, the type of violation, the wires involved, and the magnitude of the violation.
Crossed wires indicates
the two wires that are crossed.
Definition evaluation also evaluates the electrical description of loads, transmission lines, and sources for valid current nodes. The Expert MININEC Series has both intrinsic and extrinsic diagnostics. Many of the individual dialog boxes check for valid inputs. The Straight wire dialog box, for example, ensures that there are no coincident wires and that no wires have zero length.
The list of current nodes is also available under the Diagnostics option. Careful inspection of the current nodes can be used to check the model validity. The 3D display provides a three dimensional view of the problem definition for diagnostic review.
Features specific to the 3D display of the problem include
Wire numbers can be removed or displayed.
Before 3D display, the geometry is evaluated with respect to the geometry guidelines. Wires with error and warnings are highlighted in red and yellow respectively. A color coded reminder is displayed at the bottom of the screen.
The electrical depiction can be removed or displayed. Current nodes are displayed in cyan. Voltage current nodes are displayed in red and highlighted with an "S". Lumped loads current nodes are displayed in green and highlighted with a "L". Current nodes with transmission lines are displayed in magenta and highlighted with a "T". A color coded reminder is again displayed at the bottom of the screen.
Clicking on a wire in the 3D display with the right button of the mouse will highlight the wire and display a geometry description of the highlighted wire. In addition, a wire/node window is provided for deleting the wire or modifying the wire description. The geometry points and straight wires descriptions can be modified. These modifications are then reflected in the appropriate dialog boxes.
As an example, the dual quad antenna can be displayed.
As mentioned previously, the choice of the number of segments is critical to the validity of the computation. It was suggested that segments around .02 wavelengths are a reasonable choice. The Convergence test dialog box is used to define a convergence test for the problem. A convergence test consists of calculating the conductance and susceptance for the problem as the number of unknowns is increased. Since the conductance and susceptance values both converge as the number of segments are increased, the convergence test can be used to determine the accuracy that can be expected for a given segmentation density (i.e., the number of unknowns per wavelength of wire).
The TEE antenna problem can be used to demonstrate the use of the convergence test. The antenna problem in the sample file has the following definition summary. The total number of current nodes (i.e., number of unknowns) is 14. The definition summary for this TEE antenna is given below.
GEOMETRY
Dimensions in meters
Environment: PERFECT GROUND
wire caps X Y Z radius segs
1 none 0 0 0 .001 2
0 0 .04
2 none 0 0 .04 .002 6
-.12 0 .04
3 none 0 0 .04 .002 6
.12 0 .04
Number of wires = 3
current nodes = 14
minimum maximum
Individual wires wire value wire value
segment length 1 .02 1 .02
segment/radius ratio 2 9.999999 1 20.
radius 1 .001 2 .002
ELECTRICAL DESCRIPTION
Frequencies (MHz)
frequency no. of segment length (wavelengths)
no. lowest step steps minimum maximum
1 299.8 0 1 .02 .02
Sources
source node sector magnitude phase type
1 1 1 1. 0 voltage
The Convergence test dialog box displays 7 steps with a 50 percent increase in the number of unknowns for each step of the convergence test. The results for this convergence test is displayed in the table below. It is apparent that the susceptance converges faster than the conductance.
CONVERGENCE TEST Frequency = 299.8 MHz number of conductance susceptance resistance reactance unknowns (mhos) (mhos) (ohms) (ohms) source 1 of sector 1 14 9.29E-04 .0197078 2.38769 -50.6287 21 9.23E-04 .0196835 2.37604 -50.6926 28 9.16E-04 .019646 2.36836 -50.7905 35 9.1E-04 .0196017 2.36261 -50.9063 42 9.04E-04 .0195561 2.35803 -51.026 49 8.98E-04 .0195145 2.35425 -51.1356 56 8.94E-04 .0194809 2.35109 -51.2244
The Expert MININEC Series first calculates the current distribution on the defined structure. The user might want to display this current. As an example, the current distribution of the dual quad antenna can be displayed.
Next, the electric near field of the TEE antenna may be of interest. To calculate the electric near fields, the near field option must be specified, and the correct run option must be chosen. The Near field option is specified by filling the Near field dialog box. The results of the electric near field calcuations are given in the following table .
NEAR ELECTRIC FIELDS peak
Cartesian coordinate system
Frequency = 299.8 MHz
Input power = 4.65E-04 watts
location field magnitude (v/m)/phase (deg)
X Y Z X Y Z maximum
0 .1 0 0 0 2.65697 2.65697
0 0 -157.9
0 .2 0 0 0 1.09767 1.09767
0 0 -131.1
0 .3 0 0 0 .819108 .819108
0 0 -144.7
0 .4 0 0 0 .652677 .652677
0 0 -171.2
0 .5 0 0 0 .538916 .538916
0 0 158.1
0 .6 0 0 0 .45728 .45728
0 0 125.5
0 .7 0 0 0 .396366 .396366
0 0 91.8
0 .8 0 0 0 .3494 .3494
0 0 57.5
0 .9 0 0 0 .312161 .312161
0 0 22.9
0 1. 0 0 0 .281979 .281979
0 0 -12.1
As an example, the antenna pattern of the dual quad antenna may be of interest. To calculate the antenna pattern the Radiation pattern option must be specified. The radiation pattern option is specified by filling the Radiation pattern dialog box. The radiation pattern results can be displayed as a polar plot using the correct display option. The polar plot for E-phi can be displayed.
