FEKO User Manual
Contents
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5. 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 at each port It should be noted that it is not necessary to specify all possible connections If for example NWNamel Portl is connected to NWName2 Port1 it is not necessary to con nect NWName2 Portl to NWNamel Portl The user should ensure that their is enough information to link all connected ports If an internal port should be left open then no connection should be entered July 2007 FEKO User s Manual DESCRIPTION OF THE CONTROL CARDS 12 121 12 43 OF card This card specifies an offset for the origin of the coordinate system used for near and far field calculations In addition it is possible to use only a part of the structure when calculating the fields selected using labels OF Options for field calculations Calculate near field or far field on offset axis Use only some labels for field calculation Start at label End atlabel Origin of offset coordinate Parameters Calculate near field on offset axis Use the offset specified below as the origin of the coor dinate system for field calculations Use only some labels for field calculation Use label selection when calculating near and far fields Only the currents on structures wi
6. Capacitor value Value of the capacitor in F The impedance is then given by 1 12 66 p m jw If the resistance is set to zero then the resistance is interpreted as infinite i e in the parallel case it will not change the impedance The same applies to the inductance The LP card may be combined with the LD LS LZ and the SK cards but only one LP card may be used per label If a second LP card is used it replaces the values entered by the first one This card has no significance for surface elements even when these are assigned the same label July 2007 FEKO User s Manual DESCRIPTION OF THE CONTROL CARDS 12 117 12 40 LS card This card can be used to assign discrete circuit elements in series to a segment Ls Load segment with series circuit Label of segments to load Resistor value Ohm Inductor value H Capacitor value F Figure 12 30 Sketch for the serial combination Parameters Label of segments All segments with this label are assigned the series circuit values specified below Resistor value Value of the resistor in Q Inductor value Value of the inductor in H Capacitor value Value of the capacitor in F The impedance is given by Z Re job 12 67 1 es If a capacitance of zero is selected it is interpreted as infinite capacitance i e in the case of the series combination it is zero The LS card may be combined with the LD LP LZ and the SK c
7. also one wire segment could be for instance the end of one transmission line and the start of another All transmission lines ending at one wire are connected in parallel July 2007 FEKO User s Manual DESCRIPTION OF THE CONTROL CARDS 12 145 Any load impedance defined over the transmission line port segments with the LZ LS LP LD CO or SK cards are placed in series with the port parallel admittances can be defined directly at the TL card If a voltage source of type Al or A3 is applied at one of the port segments then this voltage source is assumed to be across the port i e feeding the transmission line directly with an impressed voltage Any other sources are in series with the port If S parameters are computed with respect to an excitation on a wire segment to which a TL card is connected then the LZ load may not be used at this segment The wire segments for the two ports should be located in the same medium so that the propagation constant of this medium can be taken for the transmission line If the segments are in different media then the medium of the segment at the input port is used Note that the propagation constant and thus also the propagation loss of the transmission line is the same as that of the medium surrounding input port unless an additional loss factor is specified in the Losses field If this is free space the transmission line will be lossless For transmission lines with a propagation constant that is higher
8. wire segments the LZ LS LP and LD type loads are supported These loads are placed in series with the port connection as indicated in Figure 12 27 0 add to loads i replace loads Figure 12 28 Load placement for S parameter Figure 12 27 Normal load placement calculations July 2007 FEKO User s Manual DESCRIPTION OF THE CONTROL CARDS 12 115 When a network port corresponds to an S parameter port however the use of an addi tional LZ load on that port segment is prohibited see Figure 12 28 In this instance for MoM wire segments there is in effect no difference between the Adding to existing loads and Replacing existing loads option when defining the SP card For the LN card however these two options do have an effect because of the specific placement of the load July 2007 FEKO User s Manual DESCRIPTION OF THE CONTROL CARDS 12 116 12 39 LP card This card can be used to assign discrete circuit elements in parallel to a segment Figure 12 29 shows the parallel circuit that can be assigned to a segment LP Load segment with parallel circuit Label of segments to load Resistor value Ohm Inductor value H Capacitor value F Cp Figure 12 29 Sketch of the parallel circuit Parameters Label of segments All segments with this label are assigned the parallel circuit values specified below Resistor value Value of the resistor in Q Inductor value Value of the inductor in H
9. FEKO User s Manual Suite 5 3 July 2007 Copyright 1998 2007 EM Software amp Systems S A Pty Ltd 32 Techno Avenue Technopark Stellenbosch 7600 South Africa M Tel 27 21 880 1880 Fax 27 21 880 1936 m E Mail feko emss co za NSS WWW http www feko info DESCRIPTION OF THE CONTROL CARDS 12 114 12 38 LN card This card can be used to add a complex load to any non radiating network port that is not connected to geometry i e any non radiating network of the type Internal LN Load network port with a complex impedance C Remove all LN type loads previously defined Network name Metwork port number Real part of impedance Ohm Imaginary part Ohm Parameters Define a load at a network port Define a network load with the following parameters Remove all LN type loads previously defined All previously defined LN type loads are re moved This replaces all network loads with open circuits Note that setting the load impedance to zero creates a short circuit between the network terminals Network name The network name with the network port number uniquely iden tifies the connection terminals Network port number The network port number with the network name uniquely iden tifies the connection terminals Real part of impedance The real part of the complex impedance in Q Imaginary part The imaginary part value of the complex impedance in Q For the loading of network ports connected to MoM
10. ards but only one LS card may be used per label If a second LS card is used it replaces the values entered by the first one This card has no significance for surface elements even when these are assigned the same label July 2007 FEKO User s Manual DESCRIPTION OF THE CONTROL CARDS 12 118 12 41 LZ card This card can be used to assign a complex impedance to a segment LZ Load segment with complex impedance Label of segments to load Real part of impedance Ohm Imaginary part Ohm Parameters Label of segments All segments with this label are assigned the specified impedance Real part of impedance The real part of the complex impedance in Q Imaginary part The imaginary part value of the complex impedance in Q The complex impedance value is a constant with respect to frequency Frequency depen dent impedances can be realised using the LS or the LP cards The LZ card may be combined with the LD LP LS and the SK cards but only one LZ card may be used per label If a second LZ card is used it replaces the values entered by the first one This card has no significance for surface elements even when these are assigned the same label July 2007 FEKO User s Manual DESCRIPTION OF THE CONTROL CARDS 12 119 12 42 NW card This card can be used to add a linear non radiating network NW Non radiating general network f Remove all existing networks te New network Add to existing network Ne
11. d transmis sion lines are replaced Add to existing transmission lines An additional transmission line is defined Cross input and output ports The positive port voltage is in the direction of the segment that it is connected to from the start to the end point of the seg ment Thus the input and output ports of the transmission line have unique orientations If this item is checked the transmission line connecting the ports is crossed Input port If Select label is selected in the upper group the input port the segment which represents the start of the transmission line is defined by specifying the label of the segment in the Segment label field in the lower group If more than one segment with the same label exists then the last segment with this label is used July 2007 FEKO User s Manual DESCRIPTION OF THE CONTROL CARDS 12 144 If Specify position is selected in the upper group the input port is defined by specifying the Cartesian coordinates of the centre of the segment Output port Same as for Input port but applies to the end of the transmission line Calculate length from position If checked FEKO determines the length based on the geo metrical distance between the start and end points Transmission line length The length of the transmission line in metres This value is scaled with the scaling factor of the SF card Losses Losses of the transmission line in dB m Note that since the propagation constant i
12. l A2 A3 A4 AE and AW sources are supported Al A2 and A3 sources must be selected by label not with position and unique labels must be used i e no other segments or triangles may have a label which is used for a port July 2007 FEKO User s Manual DESCRIPTION OF THE CONTROL CARDS 12 142 If the amplitude of any port is set to zero it will be used as a receive port or sink but not as a source For example if only S21 and S11 are required for a two port network one may set the amplitude of the source defining port 2 exactly to zero Then S12 and S22 are not calculated in some cases this may save considerable computation time The S parameter load impedance for each of the port sources can be specified at the source itself If no such impedance was specified the System impedance Ohm value specified with the SP card will be used if this value is not specified it defaults to 50 Q This S parameter load impedance will be added automatically to each port The only exception here are waveguide ports AW card where S parameters are related directly to the corresponding waveguide impedance It must be noted that except for waveguide ports the SP card adds load impedances to all the ports For Al A2 and A3 sources it uses LZ type loads for A4 sources it uses L4 type loads and for AE sources it uses LE type loads If any similar loads were applied to the source position before the SP card these loads will either be added or wi
13. ll be overwritten as controlled by the Always add port impedance to existing loads checkbox When execution continues after processing the SP card these loads will either be removed or kept as controlled by the checkbox Restore loads after calculation This makes a difference when for instance after the SP card the far field is computed by means of an FF card If the loads are removed then the result for the far field pattern is the same as if there was no SP card i e far field with ports not loaded by the S parameter reference impedances The disadvantage of restoring the loads is that after the SP card processing the loads change and for instance for the MoM this means that the MoM matrix changes and in order to compute the far field pattern a full extra matrix computation and LU decomposition must be done If the loads are kept then further results are readily available i e the LU decomposed matrix can be re used The original amplitudes and phases of the excitations will always be restored It should however be noted that unlike near or far field computations or some other results the amplitudes and phases of the excitations at the various ports do not influence the S parameter results except for the special case of setting the amplitude of a port to zero which indicates to FEKO that this is a passive port only This is not something special in FEKO but is how S parameters are defined i e results are normalised by the i
14. mber of ports but is required to have at least one port Port m For each port of a network can be connected to other networks or MOM wire segments Specify 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 Specify position The segment is determined by specifying the Cartesian coordinates of the segment centre These values are in metre 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 of an other network port that that has to be connected Data type The network data can be specified S parameters Z parameters or Y parameters Load data from Touchstone file The network data can be loaded from a Touchstone file 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 con sidered 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
15. ncident port signal It should in particular also be noted that setting a phase of 180 for the excitation of a port does not change the direction of this port One rather physically has to define the port the other way round e g other feed segment orientation When viewing a model in POSTFEKO then the arrows always indicate the positive source direction the arrows will also not change direction when setting a phase of the source excitation of 180 July 2007 FEKO User s Manual DESCRIPTION OF THE CONTROL CARDS 12 143 12 51 TL card This card is used to connect a non radiating transmission line between two segments TL Non radiating transmission line C Remove all existing transmission lines f New transmission line f Add to existing transmission lines Cross input and output ports Input port e Select label C Specii position Output port r Select label f Specii position Calculate length from position Transmission line length mn Losses dB m Real part of 40 Ohm Imaginary part of 20 Ohm Real part of shunt Y at port 1 Imaginary part of shunt Y at port 1 Real part of shunt Y at port Imaginary part of shunt Y at port Input port Output port Segment label Parameters Remove all existing transmission lines If checked all previously defined transmission lines are deleted All the other input parameters are ignored New transmission line Defines a new transmission line all previously define
16. s backwards compatible to the behaviour of the SP card in FEKO Suite 5 1 and earlier FEKO will automat ically add the S parameter reference loads at the various ports but possible user defined loads of the same load type see dis cussion below will be overwritten i e then not added at these ports Restore loads after calculation As discussed above FEKO automatically adds loads to ports when computing S parameters With this option the be haviour can be controlled after the SP card processing is finished If checked then the automatically added loads will be removed again and the load situation for instance for a subsequent far field request is the same as if the SP card was not used If this option is not checked then all the loads as set during the SP card processing will remain in place afterwards This was the de fault behaviour of FEKO Suite 5 1 and earlier See the discussion below regarding a potential run time impact of restoring loads re computing the MoM matrix is required then System impedance The reference impedance in Ohm This is used for all sources for which no impedance value is specified when defining the source If this field is empty it defaults to 50 Q Note that for waveg uide sources AW card S parameters are always related to the corresponding waveguide impedance The N ports must be defined before using the SP card They are identified simply by defining excitation cards Currently only A
17. s taken as the propagation constant of the medium in which the start and end segments are located the attenuation specified by this parameter is added to any losses of this medium This factor is not affected by scaling specified with the SF card i e if a scaling factor which reduces the length of the transmission line is added the total loss through the line will be less The length is now less and the loss per distance remained the same Real part of Zo Real part of the characteristic impedance of the transmission line in Ohm Imaginary part of Zo Imaginary part of the characteristic impedance of the transmis sion line in Ohm Note that the characteristic impedance only defines the ratio between the voltage and current of the two waves propagating along the line It does not specify any losses Real part of shunt Y at port 1 Real part of the shunt admittance at the input port in Siemens This admittance is across the port connecting the two wires of the transmission line Imaginary part of shunt Y at port 1 Imaginary part of the shunt admittance at the input port in Siemens Real part of shunt Y at port 2 Real part of the shunt admittance at the output port in Siemens This admittance is across the port connecting the two wires of the transmission line Imaginary part of shunt Y at port 2 Imaginary part of the shunt admittance at the output port in Siemens An arbitrary number of transmission lines can be used
18. th a label in the range specified in the fields Start at label and End at label are used during field computation If a basis function extends over for example two triangles it is included if either triangle of the tri angles lies in the specified range Origin of offset coordinate In this group the Cartesian coordinates of the transformed ori gin are specified Each of x y and z is scaled by the SF card if the SF card is used A possible application of the OF card is for example to calculate the near field on the surface of a sphere whose centre does not lie on the origin The OF card transforms the origin of the coordinate system to the centre of the sphere so that the near field calculation can be executed in spherical coordinates July 2007 FEKO User s Manual DESCRIPTION OF THE CONTROL CARDS 12 141 12 50 SP card This card is used to calculate the S parameters for the active sources SP Calculate S parameters for active sources W Always add pot impedance to existing loads Restore loads after calculation System impedance Ohm Parameters Always add port impedance to existing loads When S parameters are computed each port is automatically loaded by FEKO with the S parameter reference impedance of the port If this option is checked and the user has manually defined a load at a port then the S parameter load will be added to the existing load at the port If this option is not checked then FEKO i
19. than that of the surrounding medium such as coaxial cables filled with dielectric material one needs to reduce the length of the transmission line Losses in the transmission line network due to the shunt admittances or transmission line losses directly are taken into account and will for instance reduce antenna efficiency or gain The TL card is used in example_39 Scripting examples to create a log periodic antenna July 2007 FEKO User s Manual RET dB I ARETAN SE maB http Wwww edatop com HAMARAKTRIRA EH eS www edatop com 2006 EDA www mweda com MUREM ADS HFSS
20. twork name Humber of ports Part 1 f Specify label Segment Label Specify position f Internal port Part f Specify label x coordinate Specify position coordinate C Internal port z coordinate Por3 f Specify label Network name f Specify position Port nurmber f Internal port Data type e S rriatrix Fr matrix Y matrix Data source Load data from a Touchstone file File name The data follows in the pre file Data matrix Snr img fret The non radiating general network allows the user to do combined analysis of electro magnetics with linear circuits e g 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 and combining with FEKO geometry the complete problem solution can be found The individual element solutions are without field coupling Parameters Remove all existing networks All previously defined non radiating networks are removed July 2007 FEKO User s Manual DESCRIPTION OF THE CONTROL CARDS 12 120 New network A new non radiating network is created after removing all previ ously 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 nu
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