NW Card

This card defines a linear non-radiating network.

On the Source/Load tab, in the Loads / networks group, click the General network (NW) icon.

Figure 1. The NW - Non-radiating general network dialog.

The non-radiating general network provides functionality for combined analysis of electromagnetics with linear circuits (such as amplifiers, filters, matching networks). It is therefore possible to reduce computation time by breaking large problems into smaller element blocks. Cascading the solution of these blocks (represented by S-, Z- or Y-parameters), direct modelling of passive circuits using SPICE and combining with Feko geometry, the complete (combined) problem solution can be found. The individual element solutions defined with the NW card neglect field coupling.

Parameters:

Remove all existing networks

All previously defined non-radiating networks are removed

New network

A new non-radiating network is created after removing all previously defined networks.

Add to existing network

A non-radiating network is created and added to any previously defined networks.

Network name

The name of the network.

Number of ports

A network can consist of any number of ports, but is required to have at least one port.

Number of probes (SPICE circuit only):

The number of current/voltage probes to be added to the network. A choice is given between a Voltage probe and a Current probe. The Probe name is the name of the defined probe.

Port n

Each port of a network can be connected to other network ports or geometry. Note that the orientation of a network port connection can easily be reversed for all connections except if connected to internal ports.

Wire segment label: The label of the segment to which the network port must be connected. If more than one segment has this label, the network port is connected to the last segment with this label.
Wire segment position: The segment is determined by specifying the Cartesian coordinates of the segment centre. These values are in metres and are scaled by the SF card if Modify all dimension related values is checked.
Internal port: The network name and the network port number to connect to.
Edge between regions with multiple labels: The positive and negative labels that define the edge where the network port has to be connected.
Edge connected to ground/UTD: The positive or negative labels that define the edge where the network port has to be connected.
Edge of microstrip between two points: The points that define the edge of the microstrip line where the network port has to be connected.
Vertex by segment label: The vertex is determined by specifying a segment label. Also select whether the start or end point of that segment should be used.
Vertex by position: The vertex is determined by specifying the Cartesian coordinates of the vertex.
FEM line port position: Input port attached to a FEM line port. The position of the FEM line port is specified by the start point and end point.
Port: The port is attached to a port with label defined using the PT card.

Data type

The network data can be specified with S-parameters, Z-parameters, Y-parameters or a SPICE .cir file.

Load data from Touchstone file

The network data can be loaded from a Touchstone file (in v1.1 format). The data in a Touchstone file is always defined in increasing order and at specific frequencies only. These may of course not directly coincide with the frequencies at which the Feko kernel is run. The solution is to interpolate both the magnitude and phase data by using cubic spline interpolation. The Feko frequency is considered out of bounds when it is more than 0.1% away from the lowest/highest frequency defined in the Touchstone file. In such an instance an error will be given and Feko will terminate. If the Feko frequency is within bounds, but not between points, no interpolation will be performed.

Load data from a SPICE file

A passive circuit network can be loaded from a SPICE file.

Absolute port reference: A .cir file is to be supplied containing the required SPICE circuit description. This description should include a sub-circuit definition (..SUBCKT subnam N1 <N2 N3 ..>) with its name identical to the current NW card name. Its external number of ports should also agree in number with the number of ports defined for this NW card.
Relative port reference: A .cir file is to be supplied containing the required SPICE circuit description. This description should include a sub-circuit definition (..SUBCKT subnam N1p N1m <N2p N2m N3p N3m ..>) with its name identical to the current NW card name. Its external number of ports should be double the number of ports defined for this NW card.

Circuit name (optional)

The sub-circuit name may be specified for SPICE networks.

The data follows in the *.pre file

For small networks with four ports or less, the network matrix can be inserted directly in the .pre file. The matrix is entered as real and imaginary components. S-parameters also require a real reference impedance to be specified for each port.

For more information regarding the placement of a load when a network port is connected to segment, vertex or edge port, refer to Figure 2 and Figure 3.

Connection Guidelines

Note the following guidelines regarding the connections between network ports:

It is not necessary to specify all possible connections. If, for example, NWName1.Port1 is specified as connected to NWName2.Port1, it is not necessary to specify the reverse, that is the connection from NWName2.Port1 to NWName1.Port1. You should ensure that sufficient information is available to link all connected ports.
If an internal port should be left open, then no connection should be entered.