microwave transistor oscillator design

[ctouma01]

Hello,

I want to thank you for reading this, My professor gave me a datasheet (CEL NEC's c to X Band N-Channel GaAs MES FET | NE722S01) which have S-parameters in Common Source Configuration.

He want me to design a microwave oscillato using this datasheet on AWRmicrowaves office.
I need help to do this. Do you know how i can do this? i need to know step by step the procedure to make my project for gratuation.
The only think that he told me is may i need to change my S-parameter configuration sto common gate.

I really need your help

Thank,
Constantinos Toumazou

 

[BigBoss]

First read some textbook about oscillators.For instance Rohde's book..and Grebennikov's textbook.Make some research on the internet , also some app. notes and regarding papers,docs. etc.
There isn't any ready-to-use such oscillator design method.It's you who will define the design methodlogy.
Second you can not design oscillator by using just s-parameters.You will need also nonlinear model of that transistor.Tou should request/download nonlinear model of the transistor for Microwave Office.

 

[ctouma01]

hello again and thank you verey,very much for your reply.
I read 2-3 book and several online textbook for Oscillators

The main book i use is "Microwave Engineering, David M.Pozar"
My professor told me to read the following example to finish my project because is very useful. Also in our laboratories computers we have installed the full version of AWR Microwave office. For the non linear model you said i have the schematic which appears in the datasheet( **broken link removed** )

Untill now i have put the s parameters for the datasheet into a word pad and i saved it as a s2p file. i dont know what to do next.

EXAMPLE 13.3 TRANSISTOR OSCILLATOR DESIGN
Design a transistor oscillator at 4 GHz using a GaAs MESFET in a common
gate configuration, with a 5 nH inductor in series with the gate to increase the
instability. Choose a load network to match to a 50  load, and an appropriate
terminating network at the input to the transistor. The scattering parameters of the
transistor in a common source configuration are (Z0 = 50 ) S11 = 0.72 −116◦,
S12 = 0.03 /57◦, S21 = 2.60/ 76◦, and S22 = 0.73/ −54◦.
Solution
The first step is to convert the common source scattering parameters to the scattering
parameters that apply to the transistor in a common gate configuration with
a series inductor. (See Figure 13.9a.) This is most easily done using a microwave
CAD package. The new scattering parameters are
S11= 2.18/ −35◦,S12= 1.26/ 18◦,S21= 2.75/ 96◦,S22 = 0.52 155◦. <- HOW CAN I DO THIS Convertion?
Note that |S11| is significantly greater than |S11|, which suggests that the configuration
of Figure 13.9a is more unstable than the common source configuration.
Calculating the output stability circle (L plane) parameters from (11.25) gives
CL= 1.08 33◦

RL=0,665
Since |S11|= 2.18 > 1, the stable region is inside this circle, as shown in the
Smith chart in Figure 13.9b.
There is a great amount of freedom in our choice for L , but one objective is
to make |in| large. We therefore try several values of L located on the opposite
side of the chart from the stability circle, and select L = 0.59 −104◦. Then
we can design a single-stub matching network to convert a 50  load to ZL =
20 − j35 , as shown in Figure 13.9a.
For the given value of ΓL , we calculate in as Γin
Γin= 3.96/ −2.4◦
or Zin = −84 − j1.9 . Then, from (13.31), we find ZS as
ZS =−Rin/3 − j Xin = 28 + j1.9 .
Using Rin/3 should ensure enough instability for the startup of oscillation. The
easiest way to implement the impedance ZS is to use a 90  load with a short
length of line, as shown in the figure. It is likely that the steady-state oscillation
frequency will differ from 4 GHz because of the nonlinearity of the transistor
parameters.