Purpose:To specify radiation pattern sampling parameters and to cause program execution. Options for a field computation include a radial wire ground screen, a cliff, or surface-wave fields.

Card:

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/2|  5|   10|   15|   20|    30|    40|    50|    60|    70|    80|
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|RP |I1 | I2  | I3  | I4  |  F1  |  F2  |  F3  |  F4  |  F5  |  F6  |
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|  The numbers along the top refer to the last column in each field |
|   |   |     |     |     |      |      |      |      |      |      |
```
Parameters:
Integers
(11) - This integer selects the mode of calculation for the radiated field. Some values of (I1) will affect the meaning of the remaining parameters on the cart. Options available for I1 are:
O - normal mode. Space-wave fields are computed. An infinite ground plane is included if it has been specified previously on a GN cart; otherwise, antenna is in free space.

1 - surface wave propagating along ground is added to the normal space wave. This option changes the meaning of some of the other parameters on the RP cart as explained below, and the results appear in a special output format. Ground parameters must have been input on a GN card.

The following options cause calculation of only the space wave but with special ground conditions. ground conditions include a two medium ground (cliff) where the media join in a circle or a line, and a radial wire ground screen. Ground parameters and dimensions Must be input on a GN or GD card before the RP card is read. The RP card only selects the option for inclusion in the field calculation. (Refer to the GN and GD cards for further explanation.)

2 - linear cliff with antenna above upper level. Lower medium parameters are as specified for the second medium on the GN cart or on the GD card.

3 - circular cliff centered at origin of coordinate system: with antenna above upper level. Lower medium parameters are as specified for the second medium on the GN card or on the GD card.

4 - radial wire ground screen centered at origin.

5 - both radial wire ground screen and linear cliff.

6 - both radial wire ground screen ant circular cliff.

The field point is specified in spherical coordinates (R. sigma, theta), illustrated in figure 18, except when the surface wave is computed. For computing the surface wave field (Il = l), cylindrical coordinates (phi, theta, z) are used to accurately define points near the ground plane at large radial distances. The RP cart allows automatic stepping of the field point to compute the field over a region about the antenna at uniformly spaced points. The integers I2 and I3 and floating point numbers Fl, F2, F3 and F4 control the field-point stepping.

NTH (I2) - Number of values of theta (e) at which the field is to be computed (number of values of z for ll = l).

NPH (I3) - Number of values of phi (f) at which field is to be computed. The total number of field points requested by the card is NTH x NPH. If I2 or I3 is left blank, a value of one will be assumed.

XNDA (14) - This optional integer consists of four independent digits in columns 17, 18, 19 and 20, each having a different function. The mnemonic XNDA is not a variable name in the program. Rather, each letter represents a mnemonic for the corresponding digit in I4. If 11 = 1, then I4 has no effect and should be left blank.
X - (column l7) control output format.
X = 0 major axis, minor axis and total gain printed.
X = l vertical, horizontal ant total gain printed.

N - (column 18) causes normalized gain for the specified field points to be printed after the standard gain output. The number of field points for which the normalized gain can be printed is limited by an array dimension in the program. In the demonstration program, the limit is 600 points. If the number of field points exceeds this limit, the remaining points will be omitted from the normalized gain. The gain may be normalized to its maximum or to a value input in field F6. The type of gain that is normalized is determined by the value of N as follows:
N = 0 no normalized gain.
= 1 major axis gain normalized.
= 2 minor axis gain normalized.
= 3 vertical axis gain normalized.
= 4 horizontal axis gain normalized.
= 5 total gain normalized.

D - (column 19) selects either power gain or directive gain for both standard printing ant normalization. If the structure excitation is an incident plane wave, the quantities printed under the heading “gain” will actually be the scattering cross section (a/lambda 2 ) and will not be affected by the value of D. The column heading for the output will still read "power" or "directive gain," however.
D = 0 power gain.
D = 1 directive gain.
A - (column 20) requests calculation of average power gain over the region covered by field points.
A = 0 no averaging.
A = 1 average gain computed.
A = 2 average gain computed, printing of gain at the field points used for averaging is suppressed. If NTH or NPH is equal to one, average gain will not be computed for any value of A since the area of the region covered by field points vanishes.
Floating Point Numbers
THETS (F1) - Initial theta angle in degrees (initial z coordinate in meters if I1 = 1).

PHIS (F2) - Initial phi angle in degrees.

DTH (F3) - Increment for theta in degrees (increment for z in meters if I1 = 1).

DPH (F4) - Increment for phi in degrees.

RFLD (F5) - Radial distance (R) of field point from the origin in meters. RFLD is optional. If it is blank, the radiated electric field will have the factor exp(-jkR)/R omitted. If a value of R is specified, it should represent a point in the far-field region since near components of the field cannot be obtained with an RP cart. (If I1 = 1, then RFLD represents the cylindrical coordinate phi in meters and is not optional. It must be greater than about one wavelength.)

GNOR (F6) - Determines the gain normalization factor if normalization has been requested in the I4 field. If GNOR is blank or zero, the gain will be normalized to its maximum value. If GNOR is not zero, the gain w111 be normalized to the value of GNOR.
Notes:
• The RP card will initiate program execution, causing the interaction matrix to be computed and factored and the structure currents to be computed if these operations have not already been performed. Hence, all required input parameters Bust be set before the RP cart is read.
• At a single frequency, any number of RP cards may occur in sequence so that different field-point spacings may be used over different regions of space. If automatic frequency stepping is being used (i.e., NFRQ on the FR card is greater than one), only one RP cart will act as data inside the loop. Subsequent cards will calculate patterns at the final frequency.
• When both NTH and NPH are greater than one, the angle theta (or Z) will be stepped faster than phi.
• When a ground plane has been specified, field points should not be requested below the ground (theta greater than 90 degrees or Z less than zero.)