how control s21 phase whene design a transistor

i want to design a transistor with special phase of s21 i want to know if it is possible or not ? and how?

Hi amntt,

are you thinking of tuning the phase of S21 to your desired results? If it it, try a phase delay transmission line?

If you're thinking of designing the ACTUAL transistor and modelling its phase delay then sorry i can't help.

Natnoraa

how i can design a phase delay transmision line

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i want to have 180 degree phase between 5 to 8 ghz

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i also want isolasion between s12 and s21 can i use a delay line in the transistor drain ? so i have isolasion between input and out put and also 180degree phase . is it possible to model an ideal isolator with a transmission delay line i just want isolasion btw input and out put and phase s21=180 degree( s21=1,s12=0, phase s21=180)

Hi amntt,

you can design your phase shifter either with lumped or distributed elements.

this is for lumped elements
Source : https://www.artechhouse.com/uploads/public/documents/chapters/Bahl_CH12.pdf

for transmission line, set it to lambda/2 wavelength. but if you want a broadbrand 180 degree phase shift, you can consider a ratrace 180 degree coupler

refer to : **broken link removed**

It is impossible to have an ideal S12 of 0 (magnitude). you can increase (as in really reduce the S12) the isolation by doing a cascoding circuit as it boosts the output impedance and further enhancing the isolation between input and output ports.

Please correct me if I gave any wrong information.

Natnoraa

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Hi again,

As I am seeing and referring to your thread https://www.edaboard.com/threads/308585/#post1320585
I have a few questions:
1) what did you mean by 'don't let S12 pass'?, Your S12 is already very good from the looks of the S-param simulation. However your gain is 0dB? Check the Gmax, Fmax and Ft. without i/p and o/p matching, there should at least still be some gain.
2) why not try completing the matching network and see the results thereafter?

after these then you can add in the 180 degree ratrace coupler to your output to phaseshift S21 to 180 degree. OR if it isn't 0 degree right now, some adjustments need to be made.

Natnoraa

do u know ads? i dont know ads too much so i can not continue the simulation inorder to get matching circuite . the picture that u see its s parameter is ok is not my simulation its for a paper .
whole i want is an isolator with a transistor (btw 5 to 8 ghz i need phase shift of 180 and good isolation btw s12 and s21)
my transistor is atf3607 can u help me plot this with ads?

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i just want too simple planar isolator :sad:

Hi amntt,

Sorry but I am a newbie researcher working in a cadence environment. Have not used ADS apart from its smith chart tool. Hopefully others out there are able to give you a helping hand. but what you need should be something like this:

50 ohm port -> a 'X' degree tline for 180 degree S21 phase -> input matching -> transistor with biasing -> output matching -> 50 ohm port

then simulate in ADS environment S-param.

This is a good start to learning ADS though : **broken link removed**

even though the versions may be different but the GUI is rougly the same. Best of luck!

Natnoraa