Appreciate very much for the subtle comment of Ross. Now, it did work as expected in the analytical one. To extend the study in S-parameters, the .sp script is provided for a typical transmission line network with some stubs: IN---[Tx1]---n1---[Tx2]---n2---[Tx3]---n3---[Tx4]---OUT | | | | | | | | | [Rd] [Vin] [Sb1] [Sb2] [Sb3] | | | | | 0 0 0 0 0 (00) S-Parameters / .NET ********************************************************************* .OPTION Post + DCSTEP=1 *--[ Transmission Line (W element): XFX ]---------------------------* .subckt nom_W4x1 1 2 3 4 Len_in=10 $: Er=4.0 Zo =49.89 TD =2.03 num_sig=1 h1=4.65347 h2=4.9505 w=4 W1 1 2 3 4 Umodel=umod N=1 L=Len_in .model umod U Level=3 NL=1 Elev=2 Llev=0 Plev=1 Nlay=2 + L11=8.453n + + Cr1=3.397p + + R1c=0.252 + + Gr1=0 + + R1s=2.90989e-05 .ends nom_W4x1 *--[ Two-Port Network: Tx + Stub ]----------------------------------* * * IN---[Tx1]---n1---[Tx2]---n2---[Tx3]---n3---[Tx4]---OUT * | | | | | * | | | | [Rd] * [Vin] [Sb1] [Sb2] [Sb3] | * | | | | 0 * 0 0 0 0 *-------------------------------------------------------------------* Vin IN 0 AC 1.0 $: exciation X_Tx1 IN 0 n1 0 nom_W4x1 Len_in=1.0 $: unit = inch X_Tx2 n1 0 n2 0 nom_W4x1 Len_in=1.0 X_Tx3 n2 0 n3 0 nom_W4x1 Len_in=1.0 X_Tx4 n3 0 OUT 0 nom_W4x1 Len_in=1.0 X_Sb1 n1 0 0 0 nom_W4x1 Len_in=0.2 X_Sb2 n2 0 0 0 nom_W4x1 Len_in=0.2 X_Sb3 n3 0 0 0 nom_W4x1 Len_in=0.2 Rd OUT 0 1E14 $: open load *-------------------------------------------------------------------* .AC dec 500 1 8500Meg .NET V(OUT) Vin Rout=50.0 Rin=50.0 .probe AC S11 S11(dB) (-50,10) S11(p) (-180, 180) .probe AC S21 S21(dB) (-50,10) S21(p) (-180, 180) *-------------------------------------------------------------------* .END ********************************************************************* In brief, the S11 and S21 are referred to _________ V1+ | | V2+ --> | 2-Port | <-- Vin o-------+ +-------o Vout <-- | Network | --> V1- |_________| V2- that is, S11 = V1-/V1+ while V2+ = 0 S21 = V2+/V1+ while V2+ = 0 Nonetheless, is there well defined for S11_ni and S21_ni as depicted in the branched network? IN---[Tx1]---n1---[Tx2]---n2---[Tx3]---n3---[Tx4]---OUT | | | | | | | | | [Rd] [Vin] [Sb1] [Sb2] [Sb3] | | | | | 0 0 0 0 0 That is, at Node n1: S11=? S21=? n2: S11=? S21=? n3: S11=? S21=? Can the .NET statements be applied in the .alt statements: .alt (01) .NET V(n1) Vin Rout=50.0 Rin=50.0 .NET V(n1) Vin Rout=50.0 Rin=50.0 .probe AC S11 S21 $: node n1 .alt (02) .NET V(n2) Vin Rout=50.0 Rin=50.0 .NET V(n2) Vin Rout=50.0 Rin=50.0 .probe AC S11 S21 $: node n2 .alt (03) .NET V(n3) Vin Rout=50.0 Rin=50.0 .NET V(n3) Vin Rout=50.0 Rin=50.0 .probe AC S11 S21 $: node n3 However, it confuses me with my understanding in the 2-port network. For instance, at the node n2: IN---[Tx1]---n1---[Tx2]---n2---[Tx3]---n3---[Tx4]---OUT | | | | | | | | +----> | [Rd] [Vin] [Sb1] [Sb2] | [Sb3] | | | | | | 0 0 0 0 | 0 | | at n2: look into an open end is it needed to break/remove [Tx3... to the right of n2] by terminating at 500000ohms: IN---[Tx1]---n1---[Tx2]---n2---+[50000ohms] | | | | | | [Vin] [Sb1] [Sb2] | | | 0 0 0 such that .NET V(n2) Vin Rout=50.0 Rin=50.0 can be applied to calculate S11 and S21 at n2? What is the difference in physics between these two models: without removing [Tx3...] and 50000ohms terminated at n2? Thanks for all your sophisticated advice, indeed. _________________________________________________________________ Chat with friends online, try MSN Messenger: http://messenger.msn.com ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu