+ Post New Thread
Results 1 to 15 of 15

16th September 2019, 21:38 #1
 Join Date
 Sep 2019
 Posts
 7
 Helped
 0 / 0
 Points
 69
 Level
 1
microwave power combiner/divider
Dear all
Hi,
I have simulated a two way power combiner, two inputs port1 and port 2 are excited by two excitations with the same amplitude and combined in outport port3, but the resuts of s21 and s31 hqve a positive values (+ 2dB).
My question is, can have a positive values for s21 and s31 in dB?
I check several times my promgram, I do not know where is the problem.
I have used the fdtd method for simulation.
i have extract s21 by a ratio of the incident waveform at port 1 and the transmitted waveform at port 2 ( Fourier transforms).
i will be very grateful for your help and advice.
Best regards

17th September 2019, 05:59 #2
 Join Date
 Nov 2001
 Location
 Turkey
 Posts
 4,481
 Helped
 1346 / 1346
 Points
 30,550
 Level
 42
Re: microwave power combiner/divider
Combiners/Dividers are passive elements so they have losses, not gain..
How did you simulate his combiner?? Which EM simulator have you used ?? What is your port and substrate configuration ??

Advertisement

17th September 2019, 11:56 #3
 Join Date
 Sep 2019
 Posts
 7
 Helped
 0 / 0
 Points
 69
 Level
 1
Re: microwave power combiner/divider
We have used fdtd
configuration
inputs: port1, port2
output: port3
RT 5880
I want to know if it's right or wrong: for the calculation of s21, the two ports port1 and port2 will be excited at the same time by two excitations and we calculate the fields?

17th September 2019, 14:07 #4
 Join Date
 Nov 2001
 Location
 Turkey
 Posts
 4,481
 Helped
 1346 / 1346
 Points
 30,550
 Level
 42
Re: microwave power combiner/divider
Ports are not excited simultaneously by definition of sparameters.The simulator does not do too..
If this structure is a "Planar Wilkinson Power Divider", FDTD is a wrong choice for these type of problems.I mean, it's not wrong but it's more complicated than ought to be..
MoM or FEM Methods are very convenient and easy to configure.

17th September 2019, 18:19 #5
 Join Date
 Sep 2019
 Posts
 7
 Helped
 0 / 0
 Points
 69
 Level
 1
Re: microwave power combiner/divider
Ports are not excited simultaneously by definition of sparameters
what do you mean about this?
We have excited both ports port1 and port2, they are combined in port 3, the problem is how to extract scattering parameters?
Best regards.

18th September 2019, 17:32 #6
 Join Date
 Sep 2019
 Posts
 7
 Helped
 0 / 0
 Points
 69
 Level
 1
Re: microwave power combiner/divider
Big Boss thank you for your reply,
we have already finished our program with the fdtd method, it's part of my project.
yes power comb/div are passives components, but our results of s21 varies between + 2dB and 3 dB
s21 can have a positives and negatives values (between +3 dB an 3 dB)?
Best regards

18th September 2019, 18:29 #7

Advertisement

18th September 2019, 21:42 #8
 Join Date
 Sep 2019
 Posts
 7
 Helped
 0 / 0
 Points
 69
 Level
 1
Re: microwave power combiner/divider
Thank you BigBoss for your reply
For the power divider we have less 3dB as you say, but for power combiner (two input port1 and port2 ,one output port3) we have s21 and s31 varies between 3 dB and +2 dB, we have problem with power combiner, when we excite two input ports.
Best regards

19th September 2019, 09:04 #9
 Join Date
 Aug 2018
 Posts
 92
 Helped
 25 / 25
 Points
 711
 Level
 5
Re: microwave power combiner/divider
Depends on the correlation coefficient of your two inputs, you may get S31/S32 higher than 0dB. For example, if the combiner is ideal and you have exactly the same signal x(t) at port 1 and port 2, then port 3 outputs sqrt(2)*x(t). In this case, you will get
S32=S31=3dB.
In general, the output power is:
Pout = (P1 + P2)/2 + r(x1(t),x2(t)) * sqrt(P1*P2), where r(x1(t),x2(t)) is the correlation coefficient.
If x1(t) = x2(t), r(x1(t),x2(t)) = 1, Pout=0, S31=S32=0, all the power is lost in the combiner.Last edited by cariban; 19th September 2019 at 09:11.

19th September 2019, 10:41 #10
 Join Date
 Apr 2014
 Posts
 2,234
 Helped
 887 / 887
 Points
 14,252
 Level
 28

19th September 2019, 10:49 #11
 Join Date
 Aug 2018
 Posts
 92
 Helped
 25 / 25
 Points
 711
 Level
 5

19th September 2019, 12:41 #12
 Join Date
 Sep 2019
 Posts
 7
 Helped
 0 / 0
 Points
 69
 Level
 1
Re: microwave power combiner/divider
At this case, if I do individual port excitation, we will not have a power combiner, the input port will be divided in two other ports (power divider).
Thank you very much for your reply.
Best Regards
   Updated   
At this case, if I do individual port excitation, we will not have a power combiner, the input port will be divided in two other ports (power divider). how to exctract scattering parametters for power combiner for two inputs ports and one output port.
Thank you very much for your reply.
Best Regards

Advertisement

19th September 2019, 13:36 #13
 Join Date
 Apr 2014
 Posts
 2,234
 Helped
 887 / 887
 Points
 14,252
 Level
 28
Re: microwave power combiner/divider
For full 3port Sparameters, it is always a "black box" 3port device, and you always excite one port after another.
It seems that you are looking at one special excitation only, for the power combiner mode, so that you get 2port Sparameters only. That is possible, but your passive device must NEVER have >0dB transmission. It seems your source definition is wrong, and your total input power is 2 * 100% which leads to the wrong +3dB transmission.
1 members found this post helpful.

19th September 2019, 14:02 #14
 Join Date
 Aug 2018
 Posts
 92
 Helped
 25 / 25
 Points
 711
 Level
 5
Re: microwave power combiner/divider
1 members found this post helpful.

16th October 2019, 21:50 #15
 Join Date
 Jul 2017
 Posts
 2
 Helped
 0 / 0
 Points
 434
 Level
 4
Re: microwave power combiner/divider
Dear Dr. Volker,
Thank you for your inputs. For simulating such passive transmission line combiners/ splitters at frequencies greater than 100 GHz, which EM software do you recommend? How has your experience been with ADS momentum? I have heard mixed reviews about it.
Which mesh settings (cells/wavelength) in Momentum would you recommend for such structures? Which other setting should I worry about to get accurate results? How would RF Momentum fare as compared to Microwave Momentum at these frequencies? I know that Microwave Momentum simulator is more accurate but it takes reasonably longer simulation time as compared to former case. Since my passive structure with the ground plane is 200um X 200um with no radiation, can I rely on the results provided by RF Momentum above 100 Ghz?
Looking forward to your valuable inputs.
Thanks.
+ Post New Thread
Please login