# IE3D:What is the Terminating Impedance Zc?

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#### chowlong

##### Newbie level 4
Hi all.

I am going to design a antenna to match the chip impedance with 22-196j.
What is the Terminating Impedance Zc i need to set?

Terminating Impedance mean load impedance when calculate S11(Gamma)?

From the equation Gamma = (Zc-Zo)/(Zc+Zo),

where Zc = load impedance = terminating impedance??
Zo = source/chip impedance

So the terminating impedance = 22-195j to achieve Gamma to zero.
Am i correct?

I quite don't get what you are actually asking... however as a general rule in RF we terminate with 50 ohm or 75 ohm impedance

Hi smoothcriminal,

Now i am going to design a RFID antenna and match the chip impedance which is 22-196j

In IE3D , i want to obtain the S11 graph after simulation.

What should i set in terminating impedance Zc?

I can sure it shouldn't be 50 or 70 ohm.

Should it set to 22-195J or 22+195J?

Correct me if it is wrong.

Thanks so much=)

ok what i understand is that you want to match the source impedance to load impedance (22-196j) and you are confused whether to use 22-196j or 22+196j as terminating impedance!!!
the ans is you use "complex conjugate" of the impedance that the load is offering .. in your case load is offering 22-196j so you will use 22+196j as terminating impedance ... and match it to source impedance... you can verify it through s11 graph !! more negative amplitude in db means less relection back!!

V
Points: 2
22+195J IF you put the antenna right at the output terminal(s) of the chip. If there is a transmission line inbetween the antenna and IC, then you need to make the antenna match to a very different impedance!

In this case ,
source impedance = chip impedance (22-196j) ?
load impedance = antenna impedance( 22+196j) ?

And i agree with "the ans is you use "complex conjugate" of the impedance that the load is offering"

I think terminating impedance = 22-196j

Correct me if i am wrong.Thanks all. As you said (which you should have specified before)
source impedance = chip impedance (22-196j)
load impedance = antenna impedance( 22+196j)

we all know Zl=Zs* , which means if your load is equal to complex conjugate of your source, which is in your case as you say source is (22-196j) and load is (22+196j) then max power will travel...

This is my summarize.Am i right about the understanding of terminating impedance?

Given: chip impedance = 22-196j

Below is my approach,

Step1) design a pattern on patch antenna to obtain a Z-parameter graph

which (ideal case : antenna impedance = 22+ 195j between 860 to 940MHz)

Step2) input terminating impedance to calculate S11

( circuit diagram is attached) Zsource = chip impedance (22-195)

terminating impedance is the "complex conjugate" of the impedance that the load is offering

So terminating impedance = 22-195j

Thanks.

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