[SI-LIST] Unforeseen resonance
- From: "Loyer, Jeff" <jeff.loyer@xxxxxxxxx>
- To: "Signal Integrity Mailing List" <si-list@xxxxxxxxxxxxx>
- Date: Tue, 10 Dec 2002 09:57:29 -0800
While measuring and simulating long coupled T-lines, I came across a =
"resonance" (sudden increase in S21 magnitude loss) at a much higher =
frequency than I expected. In the simulation below, a 13.655" coupled =
T-line with a Tp of ~160pS/in has a resonance for S21 at 3.54GHz.
By my calculations, 13.655" at 160pS/in is ~2.2nS, or 457MHz. Does =
anybody know where a resonance at 3.54GHz would come from?
Spice deck:
Simulation of Long Coupled Microstrip=20
.param coupled_L=3D13.655
=20
.options INGOLD=3D1
.AC Lin 800 30K 16G
.PRINT AC S21(DB) S11(DB) S21(P) S11(P)
.NET V(N_port2) V_ACsrc ROUT=3D50 RIN=3D50
V_ACsrc N_port1 0 ac=3D1 dc=3D0
R_VNAterm N_port2 0 50Meg
* Coupled Length
W_coupled_active N_port1 N_port3 0 N_port2 N_port4 0=20
+ RLGCfile=3Drlc_5n5mil_coupled.txt N=3D2 =
L=3D'.0254*(coupled_L)'
* Terminate port 3 to 50ohms
R_port3_term N_port3 0 R=3D50
* Terminate port 4 to 50ohms
R_port4_term N_port4 0 R=3D50
.END
RLGC_file contents:
*** From To Ze Zo Se So FXtalk BXtalk
*** 1 1 49.08 - 1.91 - - -
*** 1 2 56.27 41.46 1.97 1.84 0.068 0.152
*** 2 2 49.08 - 1.91 - - -
***************************************************************
****************************
* Number of Conductors =3D 2 *
****************************
2
**************
*** Lo (H/m) *
**************
3.075197e-007 =20
5.673228e-008 3.077165e-007 =20
**************
*** Co (F/m) *
**************
1.304724e-010 =20
-1.543307e-011 1.305906e-010 =20
*****************
*** Ro (ohms/m) *
*****************
5.585039e+000 =20
0.000000e+000 5.585039e+000 =20
********************
*** Go (Siemens/m) *
********************
0.000000e+000 =20
0.000000e+000 0.000000e+000 =20
*************************
*** Rs (ohms/(m*Hz^.5)) *
*************************
2.111018e-003 =20
0.000000e+000 2.123407e-003 =20
*******************
*** Gd (S/(m*Hz)) *
*******************
1.475806e-011 =20
-1.745687e-012 1.476994e-011 =20
Jeff Loyer
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