Networks (NT)

Purpose:

To generate a two-port nonradiating, network connected between any two segments in the structure. The characteristics of the network are specified by its short-circuit admittance matrix elements. For the special case of a transmission line, a separate card is provided for convenience although the mathematical method is the same as for networks. Refer to the TL card.

Card:

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    /2|  5|   10|   15|   20|    30|    40|    50|    60|    70|    80|
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  |NT |I1 | I2  | I3  | I4  |  F1  |  F2  |  F3  |  F4  |  F5  |  F6  |
  |   |   |     |     |     |      |      |      |      |      |      |
  |   |   |     |     |     | Y11R | Y11I | Y12R | Y12I | Y22R | Y22I |
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  |   |   |     |     |     |      |      |      |      |      |      |
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  |  The numbers along the top refer to the last column in each field |
  |   |   |     |     |     |      |      |      |      |      |      |

Parameters:

Integers
(I1) - Tag number of the segment to which port one of the network is connected. This tag number along with the number to be given in (I2), which identifies the position of the segment in a set of equal tag numbers, uniquely defines the segment for port one. Blank or zero here implies that the segment will be identified, using the absolute segment number in the next location (12).

(I2) - Equal to m, specifies the m^th 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 (12) is the absolute segment number corresponding to end one of the network. A minus one in this field will nullify all previous network and transmission line connections. The rest of the card is left blank in this case.

(I3) & (I4) - Used in exactly the same way as (Il) & (I2) in order to specify the segment corresponding to port two of the network connection.

Floating point
The six floating-point fields are used to specify the real and imaginary parts of three short circuit admittance matrix elements (1, 1), (1, 2), and (2, 2), respectively. The admittance matrix is symmetric so it is unnecessary to specify element (2, 1).
Y11R (F1) - Real part of element (1, 1) in mhos.
Y11I (F2) - Imaginary part of element (1, 1) in mhos.
Y12R (F3) - Real part of element (1, 2) in mhos.
Y12I (F4) - Imaginary part of element (1, 2) in mhos.
Y22R (F5) - Real part of element (2, 2) in mhos.
Y22I (F6) - Imaginary part of element (2, 2) in mhos.

Notes:

Network cards may be used in groups to specify several networks on a structure. All network cards for a network configuration must occur together with no other cards (except TL cards) separating them. When the first NT card is read following a card other than an NT or TL card, all previous network and transmission line data are destroyed. Hence, if a set of network data is to be modified, all network data must be input again in the modified form. Dimensions in the program limit the number of networks that may be specified. In the present NEC deck, the number of two-port networks (including transmission lines) is limited to thirty, and the number of different segments having network ports connected to them is limited to thirty.
One or more network ports can be connected to any given segment. Multiple network ports connected to one segment are connected in parallel.
If a network is connected to a segment which has been impedance loaded (i.e., through the use of the LD card), the load acts in series with the network port.
A voltage source specified on the same segment as a network port is connected in parallel with the network port.
Segments can be impedance-loaded by using network cards. Consider a network connected from the segment to be loaded to some other arbitrary segment as shown in figure 17. The admittance matrix elements are Y₁₁ = 1/Z_l, Y₁₂ = 0, and Y₂₂ = infinity (computationally, a very large number such as 10¹⁰). The advantage of using this technique for loading Ls that the load can be changed without causing a recalculation of the structure matrix as in required when LD cards are used. Furthermore, in some cases a higher degree of structure matrix symmetry can be preserved because the matrix elements are not directly modified by networks as they are when using the LD cards. (Consider for instance a loop with one load where the loop is rotationally symmetric until the load is placed on it.) The disadvantage of the NT card form of loading is that the user must calculate the load admittance, and this value does not automatically scale with frequency. Obviously, in the above schematic, replacing the short with an impedance would load two segments. At a segment at which a voltage source is specified, the effect of loading by the LD nd NT cards differs, however, since the network is in parallel with the voltage source while the load specified by an LD card is in series with the source.
Use of network cards (NT) after any form of execute requires the recalculation of the current only.
NT and TL cards do not affect structure symmetry.

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