Section IV - NEC Output

Typical NEC output is illustrated in this section with examples that exercise most of the options available. In addition to demonstrating the use of the code and typical output, the results may be used to check the operation of the code when it is put in use on a new computer system. Most of the output is self-explanatory. The general form is outlined below, the particular points are discussed with the examples in which they occur.

The output follows the form of the input data, starting with the descriptive comments, followed by geometry data and then requested computations. Under the heading "STRUCTURE SPECIFICATION" is a list of the geometry data cards. The heading on the table is for a GW card, giving the X,Y, and Z coordinates of the wire ends, the radius, and the number of segments. Under the heading "WIRE NO." is a count of the number of GW cards. Data from other geometry cards are printed in the table with a label identifying the card. For a patch, the patch number is printed under "WIRE NO." followed by a letter to indicate the shape option - P for arbitrary, R for rectangular, T for triangular, and Q for quadrilateral.

After a GE card is read, a summary of the number of segments and patches is printed. The symmetry flag is zero for no symmetry, positive for planar symmetry, and negative for rotational symmetry. A table of multiple-wire junctions lists all junctions at which three or more wires join. the number of each connection segment is printed preceded by a minus sign if the current reference direction is out of the junction

Data for individual segments are printed under "SEGMENTATION DATA," including angles, alpha and beta, which are defined the same as for the patch normal vector (see figure 5). The connection data shows the connection condition at each segment. "I-" is the number of segment connected to the first end of segment I. If more than one segment connects to this junction, then I_ will be the first connected segment following I int eh sequence of segments. The numbers under "I+" give the same information for the second end of segment I. If the connection number is positive, the reference direction f the connected segments are parallel. If the number is negative, they are opposed (first end to first end, or second end to second end.) A zero indicates a free wire end, while if it is equal to I, that end of segment I is connected to a ground plane. If it is greater than 10,000 ??? end is connected to a surface and (I+-) - 10,000 is the number of the first ??? the four patches around the connection point.

When patches are used, the next section is "SURFACE PATCH DATA." This includes the coordinates of the patch center, components of the unit normal vector, and patch area. Components of the unit tangent vectors, t1 and t2 (see section II) are also printed for use in reading the surface currents printed later.

The data cards following the geometry cards are printed exactly as they are read by the program. When a card requesting computations is encountered, information on ground parameters and loading is printed, followed by currents. The line "APPROXIMATE INTEGRATION..." gives the separation distance, set by a KH card, at which the Hertzian dipole approximation is used for the electric field due to a segment. If the extended thin-wire kernel has been requested by an EK card, this is also noted at this point in the output. Under "MATRIX TIMMING" is printed the time to fill and factor the interaction matrix.

If one or more voltage sources have been specified, the voltage, current, impedance, admittance and input power are printed for each driving point. If the voltage source is the current-slop-discontinuity type, this is noted by "*" after the tag number in the input parameters table (see example 2). The antenna input parameters are followed by a table giving the current at the center of each segment. This table includes the coordinates at the segment centers and segment lengths in units of wavelength. If the model includes patches, a table of patch currents is printed giving the surface current in components along the tangent vectors t1 and t2 and X, Y, and Z components.

If there are voltage sources on a model, a power budget is printed following the current tables. The input power here is the total power supplied by all voltage sources. The structure loss is ohmic loss in wires, while the network loss is the total power into all network and transmission line ports, assuming no radiated from networks or transmission lines. Finally, the radiated power is computed as input power minus structure and network loss.

Radiated fields or near-fields requested in the input data are printed following the current tables. In the normal radiation-pattern format, transmitting antenna gains are printed in dB in the components requested on the RP card. If an incident-field excitation is used, rather than a voltage source, the gain columns will contain the bistatic scattering cross section (sigma/lamda2). For very small gains, the number -999.99 is printed.

The radiation-pattern format also includes the radiated electric field in theta and phi components. These are labeled with the units "volts/m" for E(R,theta,phi). Unless the range, Rm, is specified on the RP card, however, the quantity printed is the limit of RE(R, theta, phi) as R approaches infinity, having units of volts. the polarization is printed in a format for general elliptic polarization, including axial ratio (minor axis/major axis), tilt angle of the major axis (eta in figure 14), and sense of rotation (right-hand, left-hand, or linear).

In addition to these basic formats, there are a number of special formats for optional calculations. Many of these occur in the following examples.