SPICE s parameter measurement for one port network - help please

Am 26.11.21 um 08:34 schrieb amal banerjee:

You would need only one port of the network analyzer to connect the transmission line to the dipole. You would see then the antenna and what the transmission line does to it.

Apart of that you could measure between the 2 ports of the transmission line and then remove its influence on the dipole by math. (de-embedding)

cheers, Gerhard

I suppose his real problem is modelling the antenna. Modelling the network analyzer and the coax is easy.

I wouldn't know off hand how to model an antenna. Too many unknowns. It's not a simple 377 Ohm resistor; that much is certain.

Jeroen Belleman

The feedpoint impedance of a resonant half-wave dipole in free space is about 72 ohms.

I suspect that the OP is attempting to feed a symmetrical dipole directly with coaxial cable, without a balun. The feedline outside currents will create interesting effects on the measurements.

OK, that's a single data point.

I suspect he's trying to understand the S11 over frequency of an antenna at the far end of a piece of coax. What you say, OP?

Jeroen Belleman

Get EZnec to model your antenna.

Well... a simple first cut spice model, is simply an LC circuit!!

.SUBCKT AntennaDipoleRx_XN 1 2 in R0=75 F0=3G

• _SS_Symbol [<System>SpecialFunctions.ssm] [AntennaRX]

*Generic d1/2 wave dipole model approximation. Assumes 0.35uH/M for lambda/2 and resonating capacitor

.param vel_2=1.5e8 .param ind=0.35e-6 R1 3 2 {R0} C1 4 in {0.025330295/ind/vel_2/F0} L1 4 3 {ind*vel_2/F0} .ends

-- Kevin Aylward

SuperSpice

Fair enough. I shouldn't have bothered to answer the OP anyway. His questions are always the same: "Could some electronics guru help...", and then silence, no feedback, no additional info or questions, no conversation, nothing. He's been doing that for many years! This fellow could profit so much more if only he would entertain some dialogue.

Jeroen Belleman