How to check active reflection coefficient for all ports individually for the array antenna?

Hi, I have a four-port array antenna, where I used the active port excitation method using the "Sparameter tab", now my confusion is what are the actual active reflection coefficients in POSTFEKO? Does it refer to voltage source 1,2,3,4? Or, the active reflection coefficient results should be found under the S parameter tab in POSTFEKO? like "s11,s22,s33,s44?" Please help me by providing proper insight.

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Evan_Urban

No problem at all!

I think with your uncertainty I may also be confused. The S-Parameters such as S11 is determined by exciting port 1 and terminating all other ports. So, with this in mind, the SParameterConfiguration does this as well as the StandardConfiguration_VoltageSource1 as there is only one source and the other ports are terminated to ground.

In the case of the reflection from VoltageSource1 with all other ports being excited by another voltage source, then this isn't a true S11 result. The results are still what you observe, but I don't think it could compare against an SParameterConfiguration because it is a different scenario altogether.

So, if you do just need the reflection for VoltageSource1 with all other ports being excited by their own source, then you only have that one StandardConfiguration to use.

I hope this description helps, please let me know if I can clarify anything.

Evan_Urban

So, for the SParameterConfiguration, the Active button just means it will be considered as a transmitter in the simulation. This means it will consider 4 instances where each port will be excited and the others terminated.

Consider I have a two port system. If I have both ports active you will have for results S11, S21, S12, and S22. This can be compared by two StandardConfigurations, one having VoltageSource1 excited and Port 2 terminated, the other having VoltageSource2 excited and Port 1 terminated.

Say now I only have port 1 active, then you will only have results of S11 and S21. Having port 2 Active not selected doesn't compute S12 or S22. In this case, this is comparable to only having one StandardConfiguration where VoltageSource1 on Port1 is excited and Port 2 is terminated.

If you are interested in S-Parameters, then the SParameterConfiguration I would recommend to use for your analysis. However, if you want all ports excited at the exact same time, then this isn't an S-Parameter analysis and I would recommend to use your StandardConfiguration where all sources are applied to all ports.

I hope this helps!

Evan_Urban

Glad I could help! I apologize for the long talk, I had a misunderstanding with what your desired results were.

All comments

Evan_Urban

@sswh2, For S11, S22, S33, etc. It will refer to the list from the S-parameter configuration. So the ports listed sequentially, the first port S11, second is S22, etc. Does this help with your question?

Evan_Urban

To better visualize here's an example: Edgeport1 would be S11, Edgeport2 S22, Edgeport3 S33, and Edgeport4 S44:

Edgeport1 is only active in this case so there will only be the source port. You will see S21, S41, S31, but no S13, S23, S33, or S43 for example.

sswh2

@Evan_Urban sir, no my question was for POSTFEKO, I have coaxial probe feed, in post FEKO what is the active reflection coeeficient result? Under the voltage source tab there are reflection co efficient also under the Sparameter tab there are results for S11, S22, S33,S44 which are correct active reflection coefficient data?

Evan_Urban

I see, thank you for the description. For the S-Parameter request, no sources are defined, it goes through each port and excites them individually while terminating the others, so you get S11-S44 and so on. If you want to do the same thing but using an actual voltage source in a Standard Configuration, then you will have to have 4 Standard Configurations, each one having a different port excited and the other ports terminated. So Standard Configuration 1 will be Voltage Source 1 exciting Port 1 and all other ports terminated (50 ohms0). This will give S11-S41. Then Standard Configuration 2 will be Voltage Source 2 exciting Port 2, and Port 1, 3, and 4 terminated (S12-S42).

So for a 4 port network, if you only have Port1 Active, this means one Standard Configuration, where Voltage Source 1 is the only source applied to Port1 and the others are terminated. If all ports are active, then you need 4 Standard Configurations.

If you can share your model, I can set these up for you really quick to describe better.

sswh2

My other ports are not terminated, its active port I mean all 4 ports are simultaneously excited in CADFEKO under Sparameter "active" option I selected for four different voltage sources, but confusion came in my POSTFEKO, what should be active reflection coefficient for port 1, port 2, port 3, port 4? Should I check voltage source 1,2,3,4? or Under S parameter tab (s11,s22,s33,s44)? I am attaching here my post feko file kindly tell me.

half_arc_a_65_final_probe_4by1_array_0.46_lambda_spacing_final_coordinate_fine_mesh_more_number_of_points.pfs

Evan_Urban

The S-Parameter configuration does not consider all ports being excited at one time. The configuration will only allow one port being excited at a time and will go through all active ports. If one port isn't active you won't receive its transmit data; if Port 3 is inactive you wont get S13, S23, S33, S34, but still would get S31 for example. Ports being active is not the same as all ports excited at the same time.

Please share the .cfx file for me to investigate.

sswh2

half_arc_a_65_final_probe_4by1_array_0.46_lambda_spacing_final_coordinate_fine_mesh_more_number_of_points.cfx

Here is my CFX file where I used active port for my four coaxial probe-fed, Kindly tell me in POSTFEKO which tab will give me result ?

Evan_Urban

Please give me some time to run the simulation, it is taking a while (I have lowered the frequency increment to 10 just for purpose of explanation.)

Evan_Urban

@sswh2 Here are files for a quick simulation comparing results. In the .cfx file, you can see six configurations. One configuration is the S-Parameter configuration where all ports are active, this will get results for S11-S44. There are four configurations named with the prefix of _VoltageSource1 to _VoltageSource4, these provide the individual excitations and port terminations to obtain S11-S44. Lastly, there is the StandardConfiguration that includes all ports being excited at the same time.

From the results, you can see from the individual excitation to the S-Parameter configuration, the results align (within a couple dB at higher frequencies):

Now comparing the configuration where only VoltageSource1 is excited, the S-Parameter config S11, and the VoltageSource1 where all ports are excited, you can see the first two align but the last does not due to not being a true S-Parameter analysis:

Please let me know if you have any questions or issues with the files.

https://ftam1.altair.com/message/ZM6Ea86asIrAHidLsx0Im1

sswh2

@Evan_Urban sir thanks! Nice explanation, but after seeing the last figure, I am still not clear- IF I need the result for active reflection coefficient while all ports are simultaneously excited (the file I sent to you), then I should check which results Voltage source 1,2,3,4? or Sparameter (S11,s22,s33,s44)?

Evan_Urban

No problem at all!

So, if you do just need the reflection for VoltageSource1 with all other ports being excited by their own source, then you only have that one StandardConfiguration to use.

I hope this description helps, please let me know if I can clarify anything.

sswh2

@Evan_Urban sir, so in my cfx file I made all the ports active like this way from the "Sparameter" tab.

Now, after that, I wanted to check the reflection coefficient at each port in POSTFEKO, so from your explanation, it seems that while all ports are excited, then for checking the reflection coefficient for each port I have to go to the tab "Standard configuration then Voltage source 1, 2, 3, 4 am I correct?

sswh2

@Evan_Urban sir thanks for your detailed explanation. Now it makes sense to me- So yes, I want all ports excited at the same time, so in POSTFEKO I will check my results from "Standard configuration - voltage source1,2,3&4 instead of S parameter tab " S11,S22,S33,S44".

Thank you so much!

Evan_Urban

Glad I could help! I apologize for the long talk, I had a misunderstanding with what your desired results were.

sswh2

You are doing great! Your long explanation helped me to find out which tab in Postfeko is giving me the exact result for the active port. Its so helpful!