# SPICE s parameter measurement for one port network - help please

Started by November 26, 2021
```Could some electronics guru help me a bit ?
How would one set up S parameter measurement
for a one port network - a dipole antenna ?
Let the input be a 50 Ohm(Z0) transmission line.
What about the other end ? An impedance with the
value of tadiayion resistance 377 Ohm maybe ?
All hints, suggestions will bwgreatly appreciated.

```
```Am 26.11.21 um 08:34 schrieb amal banerjee:

> Could some electronics guru help me a bit ?
> How would one set up S parameter measurement
> for a one port network - a dipole antenna ?
> Let the input be a 50 Ohm(Z0) transmission line.
> What about the other end ? An impedance with the
> value of tadiayion resistance 377 Ohm maybe ?
> All hints, suggestions will bwgreatly appreciated.

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

```
```On 2021-11-26 09:20, Gerhard Hoffmann wrote:
> Am 26.11.21 um 08:34 schrieb amal banerjee:
>
>> Could some electronics guru help me a bit ?
>> How would one set up S parameter measurement
>> for a one port network - a dipole antenna ?
>> Let the input be a 50 Ohm(Z0) transmission line.
>> What about the other end ? An impedance with the
>> value of tadiayion resistance 377 Ohm maybe ?
>> All hints, suggestions will bwgreatly appreciated.
>
> 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
```
```On 2021-11-26 21:49, Tauno Voipio wrote:
> On 26.11.21 22.14, Jeroen Belleman wrote:
>> On 2021-11-26 09:20, Gerhard Hoffmann wrote:
>>> Am 26.11.21 um 08:34 schrieb amal banerjee:
>>>
>>>> Could some electronics guru help me a bit ?
>>>> How would one set up S parameter measurement
>>>> for a one port network - a dipole antenna ?
>>>> Let the input be a 50 Ohm(Z0) transmission line.
>>>> What about the other end ? An impedance with the
>>>> value of tadiayion resistance 377 Ohm maybe ?
>>>> All hints, suggestions will bwgreatly appreciated.
>>>
>>> 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.

OK, that's a single data point.

>
> 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.
>

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
```
```On 11/26/2021 1:34 AM, amal banerjee wrote:
> Could some electronics guru help me a bit ?
> How would one set up S parameter measurement
> for a one port network - a dipole antenna ?
> Let the input be a 50 Ohm(Z0) transmission line.
> What about the other end ? An impedance with the
> value of tadiayion resistance 377 Ohm maybe ?
> All hints, suggestions will bwgreatly appreciated.
>
>

Get EZnec to model your antenna.
```
```"Jeroen Belleman"  wrote in message news:snrf82\$1q1\$1@gioia.aioe.org...

On 2021-11-26 09:20, Gerhard Hoffmann wrote:
> Am 26.11.21 um 08:34 schrieb amal banerjee:
>
>> Could some electronics guru help me a bit ?
>> How would one set up S parameter measurement
>> for a one port network - a dipole antenna ?
>> Let the input be a 50 Ohm(Z0) transmission line.
>> What about the other end ? An impedance with the
>> value of tadiayion resistance 377 Ohm maybe ?
>> All hints, suggestions will bwgreatly appreciated.
>
> 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.

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

http://www.anasoft.co.uk/ SuperSpice
http://www.kevinaylward.co.uk/ee/index.html

```
```On 2021-11-30 10:40, Kevin Aylward wrote:
> "Jeroen Belleman"  wrote in message news:snrf82\$1q1\$1@gioia.aioe.org...
>
> On 2021-11-26 09:20, Gerhard Hoffmann wrote:
>> Am 26.11.21 um 08:34 schrieb amal banerjee:
>>
>>> Could some electronics guru help me a bit ?
>>> How would one set up S parameter measurement
>>> for a one port network - a dipole antenna ?
>>> Let the input be a 50 Ohm(Z0) transmission line.
>>> What about the other end ? An impedance with the
>>> value of tadiayion resistance 377 Ohm maybe ?
>>> All hints, suggestions will bwgreatly appreciated.
>>
>> 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.
>
> 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
>
> http://www.anasoft.co.uk/ SuperSpice
> http://www.kevinaylward.co.uk/ee/index.html

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
```