Matching network calculator

[Koen]

Hello,

      would you recommend a matching network calculator software ? Ideally offering PI matching networks and importing .S1P files ? I would like to optimize the matching of a chip input pin at a precise frequency. I have tried RFSim99 without success and would like to try another yet found nothing with the help of Google.

Thank you very much !
Koen

[rfeecs]

You might try this one, its free:
http://iowahills.com/9SmithChartPage.html
May not be what you are looking for, but it might give you a more intuitive understanding of matching, visualizing on the Smith Chart.  For single frequency, it should work.

Of course there's the paid software:
KeySight ADS http://www.keysight.com/en/pc-1297113/advanced-design-system-ads?cc=US&lc=eng
NI AWR Microwave Office http://www.awrcorp.com/products/microwave-office

Both cost a fortune, but you may have access through a company or school.

[KJDS]

Randy Rhea's "The Yin-Yang of Smith Chart Matching" has all the equations you need.

[uncle_bob]

Hi

What frequency range are you concerned with?

Matching at 100 GHz is a bit different than matching at 100 KHz.

Bob

[Koen]

Thank you for your answers. Frequencies are 400-2400MHz. It seems the problem stems from my measurements. My cheap VNA does not allow for automatic port extension to substract the measurement cable impact so is running the open/short/load calibration with the measurement cable connected to the VNA port on one side and soldered to the PCB matching network start on the other side the right way to do it ? Thank you !

[grouchobyte]

would you recommend a matching network calculator software ? Ideally offering PI matching networks and importing .S1P files ? I would like to optimize the matching of a chip input pin at a precise frequency. I have tried RFSim99 without success and would like to try another yet found nothing with the help of Google.

Thank you very much !
Koen


I use Filter Solutions. Great utility.....$13,000 USD for the license

If you speak a little Russian and know how to use Google, you can obtain it for free. 

@grouchobyte

[rfeecs]

Thank you for your answers. Frequencies are 400-2400MHz. It seems the problem stems from my measurements. My cheap VNA does not allow for automatic port extension to substract the measurement cable impact so is running the open/short/load calibration with the measurement cable connected to the VNA port on one side and soldered to the PCB matching network start on the other side the right way to do it ? Thank you !

It's not real clear what you are saying.  You have a cable soldered to the impedance you are trying to measure?  Then you are calibrating at the cable connector?

In that case you have to de-embed the cable from the measurement.  Assuming that you have a well matched cable, you have to know the insertion loss and phase shift of the cable (or S21 of the cable).  Divide your measurement by (S21)^2.  Note that you are dividing two vectors, so divide the magnitudes and subtract the angles.

So it's important that the cable is well matched and as little loss and phase shift as possible.  If the phase shift of the cable is more than 180 degrees your math gets a little more complicated.  (The phase shift of the cable goes from zero degrees at zero frequency and rotates clockwise.  To de-embed it, you have to rotate counter clockwise).

How do you know S21 of the cable?  That's another problem.  One way would be to measure a cable that is twice as long, then cut it in half.

[Koen]

Sorry if it isn't clear.

I have a PCB. On this PCB are the footprints of a PI matching network. The end of the matching network is connected to a microstrip antenna.

I have a cheap VNA. It does not provide "port extension" functionality.

I need to connect a cable from the VNA to the PCB matching network start to tune the antenna. And I need to remove the effect of the cable from the measurements.

Now, do I open/short/load calibrate at the VNA port ? Or at the cable end in free space ? Or at the cable end but soldered to the PCB matching network start ?

Thank you !

[rfeecs]

Where you calibrate sets the reference plane of your measurement.

You want to calibrate as close as you can your device under test (DUT).
You also need good quality cal standards (short, open, load).  Best is to use coaxial standards.

One way would be to calibrate at the DUT end of the cable, then connect to your board with an end launch connector:
http://www.mouser.com/new/emersonconnectivity/emerson_SMA_self-fix_endlaunch/
You may need to sacrifice a board and cut it to install the connector close to the DUT.

The other way would be calibrate at the DUT end and then substitute a cable of the same length without a connector at the DUT end and solder it to the board.  This will introduce some unwanted parasitics like the ground return inductance since it is unlikely you can maintain a nice 50 ohm transition where you solder the cable.

[uncle_bob]

Sorry if it isn't clear.

I have a PCB. On this PCB are the footprints of a PI matching network. The end of the matching network is connected to a microstrip antenna.

I have a cheap VNA. It does not provide "port extension" functionality.

I need to connect a cable from the VNA to the PCB matching network start to tune the antenna. And I need to remove the effect of the cable from the measurements.

Now, do I open/short/load calibrate at the VNA port ? Or at the cable end in free space ? Or at the cable end but soldered to the PCB matching network start ?

Thank you !

Hi

Consider that your antenna will interact with it's surroundings. Tying a cable onto the board likely messes up the near field around the antenna and changes it's impedance. You are better off just using a standard model for the antenna and calculating it's impedance.

Bob

[Koen]

Hello,

     found this with a more recent Google search : Atyune. It's free, easy, accepts .s*p, 1-4 components automatic matching and has a few libraries of components (more seem to be available by contacting Atyune).

[Bud]

Now, do I open/short/load calibrate at the VNA port ? Or at the cable end in free space ? Or at the cable end but soldered to the PCB matching network start ?

OSL calibrate at the end of the cable soldered to the pads, with the components of the matching circuit removed. Leave the end open for Open, solder a short wire between the pads for Short, and use  a 0603 50 Ohm resistor for Load calibration. This takes some time and take card of not moving the cable and board when changing cal standards. Then you will have calibration plane right at the pads. Your "cheap VNA" i guess is not a precision instrument anyway, so some errors introduced with this procedure would not affect measurement accuracy much.

But i am not sure why you want to connect the VNA to the matching circuit input. I'd think you need to measure the antenna impedance and then use a software to match it.