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[Help]Extract S-Parameters: High Power Microwave Transistor

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sinatra

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Hello all.
I need to extract the s-parameters from a High Power Mosfet microwave transistor.
I believe the models should be extracted in high power.

Basic Parameters:

Power supply= 28V
Expected RF Output Power = 150W
Operation Frequency= 460MHz
Configuration = Push-pull

I would like to know some simple method to do this parameter extraction.

Can anyone help me....??????????

S.
 

There is a simple method if you can buy a load pull system. For example.

https://www.focus-microwaves.com/

At 150 Watts output power, you might not be able to use the optimum load from the manufacture. You might also notice that RL is very low (few ohms). If you dont use the same substate/heatsink as them you might get a lot of deviation. (say 1.5 ohms deviation, that is about 50 %). You need to do your own load pull on your substate/hestsink to get a properload and S11.
 

Re: [Help]Extract S-Parameters: High Power Microwave Transis

I heard about those tuners.
They cost a lot of money and I believe their use doen't justify their price.
I'm looking for something simple that would replace those tuners and give good results anyway.
Do you know any simple way or procedure to build any kind of tuner or something similar that I could build in my place?????

S.
 

I agree with you, it is very expensive for the whole system. One alternative way is to buy only two manual tuners. It will cost you about $4000 each. you can use that tuner to do everything manually. You still need some basic equipments such as a network analyzer, signal sources, and a power meter.
 

Re: [Help]Extract S-Parameters: High Power Microwave Transis

4000US$ is quite some money anyway :'(
Have you ever seen any place where people sell this type of tuners used.....and consequently cheaper?????

Another way I tought was to use microstrip substrate and simple l match as tuner....any ideas on this????

S.
 

I have never seen 2nd hand tuner b4. At 150 watts output power, Zopt is very low. I dont know the alternative ways. You might be able to use L match as a tuner by trimming the stub. You may need to built many of L-match PCB to cover only the low impedance of the smith chart. Just an idea.
 

Re: [Help]Extract S-Parameters: High Power Microwave Transis

you could try my method as shown in the attachment.
1. put DUT into 50 ohm transmission lines test fiture board and add feedback network if necessary.
2. tune and move both Cin and Cout until meet requirements
3. take off DUT, measure the impedances of both sides presented by match circuits.

PS. those trim capacitors should be used air trim caps. for 150W
 

Re: [Help]Extract S-Parameters: High Power Microwave Transis

Hello boy and sunn and all the others.

boy:
Yes, my idea was to try something like that, an l-match and maybe make different pcbs, etc....
Those guys producers of those tuners with computer control, software, all those builtiful sometimes useless things added....They must ask a lot of money. And probably they also make a lot too.... :')

sunn:
You really made thepoint. Yes, changing the position of the trimmers we gain another degree of freedom. I would say the position of the capacitor is making the impedance transformation from the very low output impedance of the transistor to the 50ohms at the output.

And the value of the trimmer is just what is needed to cancel the reactance at the point where it is. Very nice....

The impedance of the transistor will be measured with a network analyser I expect...
Do you know any good method to measure this so low impedance of the transistor output????

S:

ps:The transistor I have is an old ldmos, pushpull 150W output 28V drain voltage.....
 

Re: [Help]Extract S-Parameters: High Power Microwave Transis

sinatra said:
The impedance of the transistor will be measured with a network analyser I expect...
Do you know any good method to measure this so low impedance of the transistor output????

ps:The transistor I have is an old ldmos, pushpull 150W output 28V drain voltage.....

I used HP 8753D to finish that job for my last project, I don't know which is best but I do know it should be calibrated properly before starting measurement.

btw, the S-Parameters you got by this method are just what transistor "want" to produce appropriate power. they are not real conjugate parts of transistor impedance.
 

Re: [Help]Extract S-Parameters: High Power Microwave Transis

I have an old hp network analyzser, I think hp8753 but I'm not sure if it is D update.

Yes, I agree with you, the impedances that will be measured should be the conjugate pairs of a certain impedance that will give optimum power, if we adjust the capacitors for maximum power....

Motorola had an old app about that but I cannt find it anymore...

S.
 

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