ardiware
Newbie level 4
Hi everybody. Excuse my english, I speak spanish. I'm doing my thesis project.
INTRODUCTION
It consist of a Low Noise Amplifier, for the band 10.7 to 13.3 GHz. I use a transistor to get a gain of 12 dB with a Noise Figure no more than 1 dB for the band.
In order to accomplish this, the transistor need a 16 ohm impedance at its input. I use a WR-75 waveguide with a caracteristic impedance of 500 ohms, so a impedance transformer is due.
3 sections Chebyshev transformer design (1/3)
**broken link removed**
**broken link removed**
3 sections Chebyshev transformer design (2/3)
**broken link removed**
**broken link removed**
3 sections Chebyshev transformer design (3/3)
According to CST MW Studio, this is the impedance at port 3 of the 3 sections transformer.
**broken link removed**
**broken link removed**
I design a 3 sections chebyshev transformer to reduce the 500 ohms to 174 ohms, then I can add a line of 50 ohms (lambda_g/4) with a stub of 6 mm (50 ohms also) to reduce the 174 ohms to 16 ohms.
Transformer plus subsystem design (1/4)
**broken link removed**
**broken link removed**
Transformer plus subsystem design (2/4)
**broken link removed**
**broken link removed**
DEVELOPMENT
I "build it" in CST Microwave Studio 5.0.1, being the waveguide of vacuum material, all of its boundaries Electrics, and the ports (1 and 2) boundaries vacuum too.
The "ridges" inside the waveguide are of PEC, with 1 mm thick. Each section has its own lambda, and ist lenght is a quarter of lambda.
I determine the impedance of each section according with the equations I attach, and then, I use CST to calcule the impedance of each section having only one "ridge" and varing its separation "s", then I wrote down the impedance calculated at 12 GHz until I got a "impedance table": for each "possible" separation 's' between "ridges" it correspond a impedance 'Z', its own lambda and its own f_cut.
So, I use the impedance calculated for CST to make each section of the transformer.
PROBLEM
As you can see in the pictures below, I'm not getting the "right" results with CST. Some of them are close (179 ohms instead of 174), but they had a very high reactance part, which should not be there.
And when I add the extra line a stub "subsystem", the results are worst. No matter the stub's length I use (from 1 to 6.25 mm, 0.2 mm step) the impedance at ports 3 and 5 stills almost the same.
Transformer plus subsystem design (3/4)
According to CST MW Studio, this is the impedance at port 3 of the transformer, plus the "subsystem"
**broken link removed**
**broken link removed**
Transformer plus subsystem design (4/4)
According to CST MW Studio, this is the impedance at port 5 of the transformer, plus the "subsystem"
**broken link removed**
**broken link removed**
I don't know whats wrong, what I'm not doing right. I suspect that my theorical calcules are not accurate, since they doesn't consider the "ridges" thickness. I have done all the calcules again using the famous chebyshev tables to determine each section impedance, but the results I get are pretty bad too.
I've hear of another approaching to calcule the impedances of each section of the transformer, they take the thickness for the calcules. If you know about them, I appreciate your help.
Anyway, thanks for reading too.
THEORICAL CALCULES
(The description is in spanish, but the equations are crystal clear)
Wave guide WR-75 and Transistor specifications
**broken link removed**
**broken link removed**
3 Sections transformer, "extraline and stub" subsystem diagram
**broken link removed**
**broken link removed**
RED: If we use a "extraline" of 50 ohms (51.9 exactly) we need a impedance matching system from 500 ohms to 173.8 ohms.
BLACK: equations used to compute each section impedance (1/2)
**broken link removed**
**broken link removed**
BLACK: equations used to compute each section impedance (2/2)
**broken link removed**
**broken link removed**
I attach the file too, if you need it.
INTRODUCTION
It consist of a Low Noise Amplifier, for the band 10.7 to 13.3 GHz. I use a transistor to get a gain of 12 dB with a Noise Figure no more than 1 dB for the band.
In order to accomplish this, the transistor need a 16 ohm impedance at its input. I use a WR-75 waveguide with a caracteristic impedance of 500 ohms, so a impedance transformer is due.
3 sections Chebyshev transformer design (1/3)
**broken link removed**
**broken link removed**
3 sections Chebyshev transformer design (2/3)
**broken link removed**
**broken link removed**
3 sections Chebyshev transformer design (3/3)
According to CST MW Studio, this is the impedance at port 3 of the 3 sections transformer.
**broken link removed**
**broken link removed**
I design a 3 sections chebyshev transformer to reduce the 500 ohms to 174 ohms, then I can add a line of 50 ohms (lambda_g/4) with a stub of 6 mm (50 ohms also) to reduce the 174 ohms to 16 ohms.
Transformer plus subsystem design (1/4)
**broken link removed**
**broken link removed**
Transformer plus subsystem design (2/4)
**broken link removed**
**broken link removed**
DEVELOPMENT
I "build it" in CST Microwave Studio 5.0.1, being the waveguide of vacuum material, all of its boundaries Electrics, and the ports (1 and 2) boundaries vacuum too.
The "ridges" inside the waveguide are of PEC, with 1 mm thick. Each section has its own lambda, and ist lenght is a quarter of lambda.
I determine the impedance of each section according with the equations I attach, and then, I use CST to calcule the impedance of each section having only one "ridge" and varing its separation "s", then I wrote down the impedance calculated at 12 GHz until I got a "impedance table": for each "possible" separation 's' between "ridges" it correspond a impedance 'Z', its own lambda and its own f_cut.
So, I use the impedance calculated for CST to make each section of the transformer.
PROBLEM
As you can see in the pictures below, I'm not getting the "right" results with CST. Some of them are close (179 ohms instead of 174), but they had a very high reactance part, which should not be there.
And when I add the extra line a stub "subsystem", the results are worst. No matter the stub's length I use (from 1 to 6.25 mm, 0.2 mm step) the impedance at ports 3 and 5 stills almost the same.
Transformer plus subsystem design (3/4)
According to CST MW Studio, this is the impedance at port 3 of the transformer, plus the "subsystem"
**broken link removed**
**broken link removed**
Transformer plus subsystem design (4/4)
According to CST MW Studio, this is the impedance at port 5 of the transformer, plus the "subsystem"
**broken link removed**
**broken link removed**
I don't know whats wrong, what I'm not doing right. I suspect that my theorical calcules are not accurate, since they doesn't consider the "ridges" thickness. I have done all the calcules again using the famous chebyshev tables to determine each section impedance, but the results I get are pretty bad too.
I've hear of another approaching to calcule the impedances of each section of the transformer, they take the thickness for the calcules. If you know about them, I appreciate your help.
Anyway, thanks for reading too.
THEORICAL CALCULES
(The description is in spanish, but the equations are crystal clear)
Wave guide WR-75 and Transistor specifications
**broken link removed**
**broken link removed**
3 Sections transformer, "extraline and stub" subsystem diagram
**broken link removed**
**broken link removed**
RED: If we use a "extraline" of 50 ohms (51.9 exactly) we need a impedance matching system from 500 ohms to 173.8 ohms.
BLACK: equations used to compute each section impedance (1/2)
**broken link removed**
**broken link removed**
BLACK: equations used to compute each section impedance (2/2)
**broken link removed**
**broken link removed**
I attach the file too, if you need it.