LTSpice simulation of a two-port network.

Thread Starter

AksharGandhi05

Joined Mar 28, 2020
4
Here's the question : "For the two port network given, obtain the Z-parameters, ABCD (transmission) parameters and h (hybrid) parameters. What should be the value of load resistance connected at Port-2 for maximum power transfer when a voltage source of 25V is connected at Port-1." (Picture attached herewith).

I have done the question by hand, but I'm having trouble writing a netlist for finding answers in the required method. If someone could help me write a netlist, I'l greatly appreciate it. I'm very new to LTSpice and have close to no experience, so some helpful resources to learn LTSpice will also be appreciated.

Values :
R1 = 20k
R2 = 6k
R3 = 25k
K = 13

These are the answers after calculation by hand :
Z - Param :
z11 = 33.45kz12 = 0
z21 = 29.146kz22 = 25k

H - Param :
h11 = 33.45kh12 = 0
h21 = -1.16h22 = 0.04m

Trans - Param :
t11 = 1.1476t12 = 28.69k
t21 = 0.034mt22 = 0.858
 

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The Electrician

Joined Oct 9, 2007
2,777
Here's the question : "For the two port network given, obtain the Z-parameters, ABCD (transmission) parameters and h (hybrid) parameters. What should be the value of load resistance connected at Port-2 for maximum power transfer when a voltage source of 25V is connected at Port-1." (Picture attached herewith).

I have done the question by hand, but I'm having trouble writing a netlist for finding answers in the required method. If someone could help me write a netlist, I'l greatly appreciate it. I'm very new to LTSpice and have close to no experience, so some helpful resources to learn LTSpice will also be appreciated.

Values :
R1 = 20k
R2 = 6k
R3 = 25k
K = 13

These are the answers after calculation by hand :
Z - Param :
z11 = 33.45kz12 = 0
z21 = 29.146kz22 = 25k
H - Param :

h11 = 33.45kh12 = 0
h21 = -1.16h22 = 0.04m
Trans - Param :

t11 = 1.1476t12 = 28.69k
t21 = 0.034mt22 = 0.858
Have you checked your hand-derived result for correctness? For example, If you apply 1 volt to the input port 1 of your Two-port, what is the output voltage at Port 2? What is the result when the original network is tested this way?
 

Thread Starter

AksharGandhi05

Joined Mar 28, 2020
4
Have you checked your hand-derived result for correctness? For example, If you apply 1 volt to the input port 1 of your Two-port, what is the output voltage at Port 2? What is the result when the original network is tested this way?
Yes, I realize I've committed an error. I've solved this now, thank you for your time.
 

Thread Starter

AksharGandhi05

Joined Mar 28, 2020
4
Z - parameters
z11 = 22.68k ohmz12 = 0 ohm
z21 = 5.806 ohmz22 = 25k ohm

H-parameters
h11 = 22.68k ohmh12 = 0
h21 = -0.232mh22 = 0.04m mho

T-parameters
t11 = 3.906kt12 = 9.76e07 ohm
t21 = 0.172t22 = 4.30k
 

The Electrician

Joined Oct 9, 2007
2,777
I get the same values you have.

In the first post, you mention "finding answers in the required method. " Is there a method for finding two-port parameters using LTSpice? Is it doing something more than one would do by hand, but with the calculations done by LTSpice?
 

The Electrician

Joined Oct 9, 2007
2,777
FYI, there is a short method to derive the two-port Z parameters for the original circuit.

Write an admittance (Y) matrix for the circuit by inspection. Invert the Y matrix to obtain a Z matrix, and delete the rows and columns corresponding to the two interior nodes of the original circuit. The remaining elements (in red) are the two-port Z parameters. The transformations to h and T parameters are almost trivial.

Forum TwoPort.png
 

Thread Starter

AksharGandhi05

Joined Mar 28, 2020
4
I get the same values you have.

In the first post, you mention "finding answers in the required method. " Is there a method for finding two-port parameters using LTSpice? Is it doing something more than one would do by hand, but with the calculations done by LTSpice?
I assumed there was a method, all I had to do was connect an arbitrary voltage source at port 1 and keep port 2 open-circuited to get z11, and step by step keep shifting values this way to get the desired parameters.
It's quite simple really now that I see it. Hope this helps.
 
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