Understanding N-Port Parameters for Microwave Networks

[seang]

In my previous classes we did just a bit of 2 port stuff. Where you shorted one port and then you just divided port 1's current by port 1's voltage and bam. Now we're starting to learn about n port microwave networks, and I really want to know what's going on. This post will probably be filled with questions so thanks in advance for any help.

Alright, so back to basics, let's just say I have a basic (low freq) 2 port network and I'm about to find the y parameters. Let's say I'm finding in particular y11. I divide port 1's current by port 1's voltage. What exactly have I found? You know? this is what's troubling me. I'm thinking since port 2 is shorted during measurement, y11 is the admittance of the network? That's all I can think of, and I am even more clueless for y12, y21, y22. I have no idea what these quantities mean or what they say about the network.

Now the other half of the puzzle...the equations:

I1 = (y11*V1) + (y12*v2)
I2 = (y21*V1) + (y22*v2)

I don't really understand these equations. I think I might have a better handle on them if i could get my head around the meanings of y11...y22. But if anyone can put these equations into words that would probably help alot.

Oh yeah, can anyone recommend a text on this kind of thing? my microwave texts assume i already know all this stuff really well, and my previous texts don't really cover the basics. i need something to cover the gap i guess.

 

[Corneo]

Ok I assume you know what's Z parameters.

y11 = I1/V1 (with V2 = 0, short port 2)

This represents the input admittance seen looking into port 1. Much like Z11 would be the input impedance seen looking into port 1.

y21 would be the transfer admittance seen looking from port 1 to port 2.

transfer admittance and transfer impedances makes more sense when you learn S - parameters.

 

[ravenprp]

Hi there,

It's great that you are taking an interest in learning about N-port parameters for microwave networks. It can definitely be a bit confusing at first, but with some practice and understanding, you'll be able to grasp the concepts.

To start off, let's clarify what N-port parameters are. N-port parameters are a set of values that describe the behavior of an N-port network. In your example, you were working with a 2-port network, so you were finding the Y-parameters, which are used to describe the network's admittance.

Now, let's break down the meaning of Y-parameters. Y11 represents the admittance of port 1 when port 2 is shorted. Similarly, Y22 represents the admittance of port 2 when port 1 is shorted. Y12 and Y21 represent the cross-admittance between ports 1 and 2. In simpler terms, these parameters tell us how much current flows through a port for a given voltage input.

So, when you divide port 1's current by port 1's voltage, you are essentially finding the admittance of port 1 when port 2 is shorted. This value can tell you how easy or difficult it is for current to flow through port 1.

Now, onto the equations. These equations are simply a representation of Kirchhoff's current law, which states that the sum of currents entering a node must equal the sum of currents leaving that node. In this case, the node is the two-port network, and the equations are showing the relationship between the currents and voltages at each port.

As for a recommended text, I would suggest "Microwave Engineering" by David M. Pozar. It covers the basics of microwave networks and N-port parameters in a clear and concise manner.

I hope this helps clarify some of your questions. Keep practicing and don't hesitate to ask for help if you need it. Best of luck in your studies!