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Equipment for impedance matching of

yefj

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Hello,I have a tansistor with the following caracteristics. i need to build a matching network for it. to get Max Gain as shown bellow.
assuming i will buy the network analizer bellow.
the problem is with the SMA cable, I cant connect it to the transistor on my breadboard.
what is the proper connector i should use to connect the SMA (that is connected to the network analyzer) so i get a correct reading of the impedance of the transistor?
Thanks.


1602935868864.png
 

FvM

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It makes no sense to implement a matching network or measure impedances at GHz frequencies on a breadboard.

The minimum is to solder the components on a RF vero board with continuous ground plane.
 

yefj

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Hello VFM , i know that impedance is on a single frequency.i dont want to match by guess without calculation my amplifier.
I ask purely regarding how to connect network analizer with my tansistor?
SMA connection is not possible.
What are the options to read impdenace from transistor leg on bread board.
 
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BigBoss

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Bread-Board is NOT proper substrate for RF.You should already have known this..
 
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yefj

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Hello Big Boss, You are correct, so two questions:
1.what is the alternative for a homemade newbiew circuit builder?
2. what cable suitable for measuring impedance on a amplifier using network analizer?
Thanks.
 

vfone

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An "ugly construction" will behave much better for prototyping (up to 1GHz or 2GHz), compared to a breadboard which is limited to very low frequencies.

The VNA that you posted works fine up to 3GHz, the dynamic range is a bit low between 1.5GHz and 3GHz, but will do the job.
You need good quality coax cables to do the impedance measurements (and the VNA calibration), at least like these ones:
 

Georgy.Moshkin

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One option is to design and order custom amplifier FR4 board and solder side-mount SMA connectors. You can put several test lines on a single PCB: through line, open-ended line, amplifier itself, etc. Maybe some resonator to check if Er is far from 4.5. It will take some time to learn these things, how to make good layout, how to place an order, but it will be more productive. By measuring through line you can ensure that SMA connectors do not introduce significant impedance mismatch. If there are some unexpected readings from VNA, then something is wrong with design or measurement setup, and it must be fixed.
Another option is to buy some readily available amplifier board with a _known_ transistor, then use VNA to reverse-engineer it. I think it may be even better option to start in this field.
 

yefj

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the board is flat and i need to pin the cable on the transistor leg and GND
i cannot do this operation with SMA .
is there some other solution then cutting the SMA and putting the outer coating to the GND and inner part on the leg?(i am afraid it will mess up a reading)

An "ugly construction" will behave much better for prototyping (up to 1GHz or 2GHz), compared to a breadboard which is limited to very low frequencies.

The VNA that you posted works fine up to 3GHz, the dynamic range is a bit low between 1.5GHz and 3GHz, but will do the job.
You need good quality coax cables to do the impedance measurements (and the VNA calibration), at least like these ones:
 

FvM

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i need to pin the cable on the transistor leg and GND i cannot do this operation with SMA.
Sounds confused.
Firstly you need to bias the transistor in an amplifier circuit to measure impedances, respectively you surely don't connect the VNA ports directly to a transistor.
Secondly the board termination (transistors leads, PCB pads) becomes part of the effective transistor incircuit impedance seen by your matching circuit. You want to probe the transistor in a geometry similar to the final circuit assembly, whatever it is.

SMA connectors may be too large in some situations, in this case an adapter to a smaller connector or fixed coax cables may be used to connect a device under test. The problem is that the VNA has to be calibrated to a reference plane near the device, and you need a calibration kit or at least temporary calibration impedances that can be attached at the reference plane. Alternatively you have to assume the final transmission line between SMA connector and the device as ideal 50 ohm line which introduces additional errors.
 

BigBoss

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Hello Big Boss, You are correct, so two questions:
1.what is the alternative for a homemade newbiew circuit builder?
2. what cable suitable for measuring impedance on a amplifier using network analizer?
Thanks.
Even you cut a double sided FR4 by aid of a simple cutter to create the RF island, it will be much better than breadboard.
Don't worry about cables, you can find many high quality,even phase corrected cables in the market but you first of all have to know how to implement a RF board.
 

vfone

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is there some other solution then cutting the SMA and putting the outer coating to the GND and inner part on the leg?(i am afraid it will mess up a reading)
Up to about 500MHz you can do this cutting and do the OPEN, SHORT, and LOAD calibration on port 1, and THROUGH between port 1 and port 2 (the VNA you posted I think doesn't support single port calibration on port 2). Use for load an SMD 50 ohms resistor.
Ideally would be to use two 50 ohms semi-rigid coax cables with SMAs at one end.


After VNA calibration, if you connect the VNA cables to your circuit, be sure there are DC blocking capacitors in place to don't damage the VNA input, even this is not an expensive one.
 

yefj

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Hello,What could be done at 3Ghz?
Thanks.

Up to about 500MHz you can do this cutting and do the OPEN, SHORT, and LOAD calibration on port 1, and THROUGH between port 1 and port 2 (the VNA you posted I think doesn't support single port calibration on port 2). Use for load an SMD 50 ohms resistor.
Ideally would be to use two 50 ohms semi-rigid coax cables with SMAs at one end.


After VNA calibration, if you connect the VNA cables to your circuit, be sure there are DC blocking capacitors in place to don't damage the VNA input, even this is not an expensive one.
 

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