## Excitation (EX)

Purpose: To specify the excitation for the structure. The excitation can be voltage sources on the structure, an elementary current source, or a plane-wave incident on the structure.

Card:

```     _________________________________________________________________
/2|  5|   10|   15|   20|    30|    40|    50|    60|    70|    80|
/  |   |     |     |     |      |      |      |      |      |      |
|   |   |     |     |     |      |      |      |      |      |      |
|EX |I1 | I2  | I3  | I4  |  F1  |  F2  |  F3  |  F4  |  F5  |  F6  |
|   |   |     |     |     |      |      |      |      |      |      |
|   |   |     |     |     |      |      |      |      |      |      |
|   |   |     |     |     |      |      |      |      |      |      |
|   |   |     |     |     |      |      |      |      |      |      |
|   |   |     |     |     |      |      |      |      |      |      |
|   |   |     |     |     |      |      |      |      |      |      |
|   |   |     |     |     |      |      |      |      |      |      |
|  The numbers along the top refer to the last column in each field |
|   |   |     |     |     |      |      |      |      |      |      |
```
Parameters:
Integers
(I1) - Determines the type of excitation which is used.
O - voltage source (applied-E-field source).
1 - incident plane wave, linear polarization.
2 - incident plane wave, right-hand (thumb along the incident k vector) elliptic polarization.
3 - incident plane wave, left-hand elliptic polarization.
4 - elementary current source.
5 - voltage source (current-slope-discontinuity).
Remaining Integers Depend on Excitation Type
a. Voltage source ((I1) - O or 5)
(I2) - Tag number the source segment. This tag number along with the number to be given in (I3), which identifies the position of the segment in a set of equal tag numbers, uniquely definer the source segment. Blank or zero in field (I2) implies that the Source segment will be identified by using the absolute segment number in the next f field.

(I3) - Equal to m, specifies the mth segment of the set of segments whose tag numbers are equal to the number set by the previous parameter. If the previous parameter is zero, the number in (I3) must be the absolute segment number of the source.

(I4) - Columns l9 ant 20 of this field are used separately
The options for column l9 are:
1 - maximum relative admittance matrix asymmetry for source segment and network connection will be calculated and printed.

0 - no action.
The options for column 20 are:
l - the input impedance at voltage sources is always printed directly before the segment currents in the output. By setting this flag, the impedance of a single source segment in a frequency loop will be collected ant printer in a table(in a normalized and unnormalized form) after the information at all frequencies has been printed. Normalization to the maximum value is a default, but the nonnalization value can be specified (refer to F3 under voltage source below). When there is more than one source on the structure, only the impedance of the last Source specified will be collected .

0 - no action
b. Incident plane wave ((I1) - 1, 2, or 3)
(I2) - Number of theta angles desired for the incident plane wave .
(I3) - Number of phi angles desired for the incident plane wave.
(I4) - Only column l9 is used. The options are:
1 - maximum relative admittance matrix asymmetry for network connections will be calculated and printed.
0 - no action
c . Elementary current source ( (Al) = 4)
(12) & (13) - blank.
(I4) - Only column l9 is used and its function is identical to that listed under b.
Floating Point Options
a. Voltage source ( (Al) " 0 or A)
(Fl) - Real part of the voltage in volts.
(F2) - Imaginary part of the voltage in volts. (F3) - If a one Is placed in column 20 (see above), this field can be used to specify a normalization constants for the impedance printed in the optional impedance table. Blank in this field produces normalization to the maximum value.
(F4), (F5), & (F6) - Blank.
b. Incident plane wave ((11) s 1, 2, or 3). The incident wave is characterized by the direction of incident ^k wave polarization in the plane normal to ^k.
(F1) - Theta in degrees. Theta 19 defined in standard spherical coordinates as illustrated in figure 14.
(F2) - Phi in degrees. Phi is the standard spherical angle defined lned in the XY plane.
(F3) - Eta in degrees. Eta is the polarization angle defined as the angle between the theta unit vector and the direction of the electric field for linear polarization or the major ellipse axis for elliptical polarization. Refer to figure 14,
(F4) - Theta angle stepping increment in degrees.
(F5) - Phi angle stepping increment in degrees.
(F6) - Ratio of minor axis to major axis for elliptic polarization (major axis field strength - 1 V/m).
C. Elementary current source ((I1) - 4). The current source is characterized by its Cartesian coordinate position, orientation, and its magnitude.
(F1) - X position in meters.
(F2) - Y position in meters.
(F3) - Z position in meters.
(F4) - a in degrees. a is the angle the current source makes with the XY plane as illustrated on figure 15.
(F5) - beta in degrees. beta is the angle the projection of the current source on the XY plane makes with the X axis.
(F6) - "Current moment" of the source. This parameter is equal to the product Il in amp meters.
Notes:
• In the case of voltage sources, excitation cards can be grouped together in order to specify multiple sources. The maximum number of voltage sources that may be specified is determined by dimension statements in the program. The dimensions are set for 10 applied-E- field voltage sources and 10 current-slope-discontinuity voltage sources.
• The applied-E-field voltage source tat located on the segment specified.
• The current-slope-discontinuity source is located at the first end, relative to the reference direction, of the specified segment, at the Junction between the specified segment and the previous segment. This Junction must be a simple two-segment Junction. and the two Segments must be parallel with equal lengths ant radii.
• A current-slope-discontinuity voltage source may lie in a symmetry plane. An applied field voltage source may not lie in a symmetry plane since a segment may not lie in a symmetry plane. An applied field voltage source may be used on a wire crossing a symmetry plane by exciting the two segments on opposite sides of the Symmetry plane each with half the total voltage, taking account of the reference directions of the two segments.
• An applied field voltage source specified on a segment which has been impedance-loaded, through the use of an LD card, is connected in series with the loads An applied field voltage source specified on the same segment as a network is connected in parallel with the nee- work port. For the specific care of a transmission line, the source is in parallel with both the line ant the shunt load. Applied field voltage sources should be used in these cases since loads and network connections are located on, rather that between, segments.
• Only one incident plane wave or one elementary current source is al- lowed at a time. Also plane-wave or current-source excitation is not allowed with voltage sources. If the excitation types are mixed, the program will use the last excitation type encountered.
• When a number of theta and phi angles are specified for an incident plane-wave excitation, the theta angle changes more rapidly than phi.
• The current element source illuminates the structure with the field of an infinitesimal current element at the specified location. The current element source cannot be used over a ground plane.