How to Combine S Parameter Results at a port for an antenna that uses multiple ports?

[Komal Srivastava]

Hello guys,
I am using CST.I am implementing Full Duplex wireless communication using Antenna Cancellation Technique, where i am using two transmitters at a distance of d and d+lambda/2 from the receiver to nullify the self interference(see the diagram).

For this i am using two transmitters and one receiver(I am using monopole).To make this i am exciting only ports 2 and 3 which I am considering as transmitters(see the diagram).

I am facing the problem that i am not receiving any change in my s12 n s13 parameters when i am exciting port 2 n port 3 simultaneously; from the one in which i am exciting only port 1 or only port 2.

ie.s12 when only port 2 is excited should be different from the s12 that i am getting from simultaneous excitation of port 2 n 3(coz it wud inculcate the effect of port 3 as well).
Either i am not exciting my Tx antennas correctly or the S parameter results are not getting combined correctly.

Kindly help me to get my results.Any help wud be highly appreciated.Thanks in advance.

 

[volker@muehlhaus]

I am facing the problem that i am not receiving any change in my s12 n s13 parameters when i am exciting port 2 n port 3 simultaneously; from the one in which i am exciting only port 1 or only port 2.

Is this a basic problem with understanding S-parameters?

S12 is the transmission from port 2 to port 1 (excitation at port 2 only, no excitation at other ports)
S13 is the transmission from port 3 to port 1 (excitation at port 3 only, no excitation at other ports)

So if you look at the basic 3-port S-parameters, you never see cancellation in S12 or S13 because two antennas are never transmitting simulateously. To check cancellation, you need to check the magnitude and phase of S12 and S13, to see if both signals have equal magnitude with 180° phase shift.

 

[Komal Srivastava]

Is this a basic problem with understanding S-parameters?

S12 is the transmission from port 2 to port 1 (excitation at port 2 only, no excitation at other ports)
S13 is the transmission from port 3 to port 1 (excitation at port 3 only, no excitation at other ports)

So if you look at the basic 3-port S-parameters, you never see cancellation in S12 or S13 because two antennas are never transmitting simulateously. To check cancellation, you need to check the magnitude and phase of S12 and S13, to see if both signals have equal magnitude with 180° phase shift.

Thanks for the reply.Yes you are right.I need to check mag n phase of s12 n s13.

But I am new to CST.Kindly help me doing this in CST ie checking magnitude with 180 phase shift.
Thanks in advance.

 

[Komal Srivastava]

Thanks for the reply.Yes you are right.I need to check mag n phase of s12 n s13.

But I am new to CST.Kindly help me doing this in CST ie checking magnitude with 180 phase shift.
Thanks in advance.

I cud calculate S12 n S13 phase and magnitude.Magnitude is almost same and phase is almost 160 degrees.

These values ensures cancellation but i have a doubt that whether there is any calculation of the amount of cancellation in CST.

Also is there any way to measure Isolation between two ports.Thanks in advance.

 

[volker@muehlhaus]

These values ensures cancellation but i have a doubt that whether there is any calculation of the amount of cancellation in CST.

I am not a CST user so I don't know what is the best way to do it. I would use a schematic with power splitter to drive the two antenna ports with same signals, and measure transmission to the receiving antenna.

Or calculate signal by hand: 1.0 + 1.0*cos(160°) = 0.06

Also is there any way to measure Isolation between two ports.

S23

 

[Komal Srivastava]

Thanks for your reply.I have a little confusion with Radiation Patterns.Kindly give me a rough idea of theta and phi in Radiation Pattern.That wud be really helpful.

I am using a monopole which has an omnidirectional Pattern.Now Txrs 2 n 3 are excited to cancel the signal received at Rx 1.

What wud be the effect of this cancellation on Radiation pattern.What should be the resultant pattern?

Thanks in Advance.