Continue to Site

# Transmission and Reflection coefficient from S parameter

Status
Not open for further replies.

#### nijasmhmmd

##### Newbie level 3
Hi Friends....
Can anyone give the relation between Transmission ,reflection coefficient and s parameter.

In my case load is not perfectly matched.
I know one equation for Reflection coefficent
Γin=S11+( S12*S21*ΓL)/(1-S22*ΓL)
But how to find out ΓL:?:

Nijas

ΓL=S22+( S12*S21*Γin)/(1-S11*Γin)

### nijasmhmmd

Points: 2
my main target is how to find out Γin.

Finding Reflection and Transmission coefficent from other paramter also helpfull for my calculation....

Nijas

For single frequency one can calculate Γin as per the equation above.
So you need to have ΓL and S-para data.
ΓL for 50 ohm char impedance will be (ZL-50)/(ZL+50).
ΓL=S22+( S12*S21*Γin)/(1-S11*Γin) equation is valid when there is DUT with bi-directional behavior like amplifier etc.
In this case ΓL is depend on Γin and vice varsa.

### nijasmhmmd

Points: 2
Can you give any formula for Transmission coefficient....

kspalla said:
Can you give any formula for Transmission coefficient
1-ΓL

For a LOSSLESS network, you can say the (POWER into the network) = (POWER reflected off the network) + (POWER transmitted thru the network)

The old "conservation of power" rule.

Γ is a VOLTAGE reflection coefficient. If you are concerned about POWER, you would be more interested in VOLTAGE²/impedance=POWER. SO POWER is proportional to Γ².

If you normalize the input POWER to equal "1", you can then say that:

1 = Γ² + τ²

So the transmission coefficient is:

τ = √(1-Γ²)

Input reflection coefficient is S11,
Output reflection coefficient ( that is ration of power reflected from load to power transmitted towards load)
Transmission coefficient is S12 or you can say isolation
& S21 is gain.

Microwave transistor amplifiers.

nijasmhmmd said:
Hi Friends....
Can anyone give the relation between Transmission ,reflection coefficient and s parameter.

In my case load is not perfectly matched.
I know one equation for Reflection coefficent
Γin=S11+( S12*S21*ΓL)/(1-S22*ΓL)
But how to find out ΓL:?:

Nijas
eq. (Γin=S11+( S12*S21*ΓL)/(1-S22*ΓL))?

It does not make any sense if we simply tell the formular from books. You'd better read them yourself. There are many books you can refer to, such as "Microwave Eningeering" and "RF Circuit Design".

can any one tell me what are s parameters of amplifier n what there values tell about for eg if S11 is input impedance and for rf amplifier it should be less that -10db so why is that so? if u have some links or tutorials so plz refer.

Status
Not open for further replies.