The program control cards follow the structure geometry cards. They set electrical parameters for the model, select options for the solution procedure, and request data computation. The cards are listed below by their mnemonic identifier with a breif description of their function:
Group I EK - extended thin-wire kernal flag FR - fequecy specification GN - ground parameter specification KH - interaction approximation range LD - structure impedance loading Group II EX - stucture excitation card NT - two-port network specification TL - transmission line specification Group III CP - coupling calculation EN - end of data flag GD - additional graound parameter specifications NE - near electric field request NH - near magnetic field request NX - next stucture flag PQ - wire charge density print control PT - wire-current print control RP - radiation pattern request WG - write Numerical Green's Function file XQ - execute card
There is no fixed order for the cards. The desired parameters and options are set first followed by requests for calculation of currents, near fields and radiated fields. Parameters that are not set in the input data are given default values. The one exception to this is the excitation (EX) which must be set.
Computation of currents may be requested by an XQ card. RP, NE, or NH cards cause calculation of teh currents and radiated or near fields on the first occurrence. Subsequent RP, NE, or NH cards cause computation of fields using the previously calculated currents. Any number of near-field and radiation-pattern requests may be grouped together in a data deck. An exception to this occurs when multiple frequencies are requested by a single FR card. In this case, only a single NE or NH card and a single RP card will remain in effect for all frequencies.
All parameters retain there values until changed by subsequent data cards. Hence, after parameters have been set and currents or fields computed, selected parameters may be changed and the calculatios repeated. For example, if a number of different excitations are required at a single frequency, the deck could have the form FR, EX, XQ, EX, XQ, ... If a single excitation is required at a number of frequencies, the cards EX, FR, XQ, FR, XQ, ... could be used.
When the antenna is modified and additional calculations are requested, the order of the cards may, in some cases, affect the solutiontime since the program will repeat only that part of the solution affected by the changed parameters. For this reason, the user should understand the relation of the data cards to the solution procedure. The first step in the solution is to calculate the interaction matrix, which determines the response of the antenna to an arbitrary excitation, and to factor this matrix in preparation for solution of the matrix equation. This is the most time-consuming single step in the solution procedure. The second step is to solve the matrix equation for the currents due to a specific excitation. Finally, the near fields or radiated fields may be computed from the currents.
The interaction matrix depends only on the structure geometry and the cards in group I of the program control cards. Thus, computation and factor- ization of the matrix is not repeated if cards beyond group I are changed. On the other hand, antenna currents depend on both the interaction matrix and the cards in group II, so that the currents must be recomputed whenever cards in group I or II are changed. The near fields depend only on the structure currents while the radiated fields depend on the currents and on the GD card, which contains special ground parameters for the radiated-field calculation. An example of the inplications of these rules is presented by the following two sets of data cards:
FR, EX, NT1, LD1, XQ, LD2, XQ, NT2, LD1, XQ, LD2, XQ FR, EX, LD1, NT1, XQ, NT2, XQ, LD2, NT1, XQ, NT2, XQ
Calculation and factoring of the matrix would be required four times by the first set but only twice by the second set in obtaining the same information.
The program control cards are explained on the following pages. The format of all program control cards has four integers and six floating point numbers. The integers are contained in columns 3 through 5, 6 through 10, 11 through 15, and 16 through 20 (each integer field stops at an integral multiple of 5 columns), and the floating point numbers are contained in fields of 10 for the remainder of the card (i.e., from 21 through 30, 31 through 40, etc.). Integers are right justified in their fields. The floating point numbers can be punched either as a string of digits containing a decimal point, punched anywhere in the field; or as a string of digits containing a decimal point and followed by an exponent of ten in the form E +- I which multiplies the number by 10^+-I. The integer exponent must be right justified in the field.