VNA Resistive Power Splitter and Cal kit Design Help

[RomDump]

Hey Guys,

Need a little help here. I am trying to learn on using a Agilent 4395A VNA but I don't have any accessories and don't want to spend a ton of money on this.

Wondering is any one has some tips on building a 50ohm BNC resistive power splitter PCB.

Also I don't have a Cal kit for the 4395A so would like make up a simple open and short test adapters.

Any tips and ideas?

Thanks.

[Jay_Diddy_B]

Hi RomDump and the group,

You could start with a PCB design like this one:




This a link to the website where I found this one:

https://www.mariohellmich.de/projects/trl-cal/trl-cal.html#_

This is designed using a technique called coplanar waveguide. The width of the track and the spacing to the ground plane are chosen to make the trace 50 .

Additions or Alternatives

Schematic




Here are some other ideas. I have drawn a splitter, an attenuator and a low pass filter.

PCB
This how I would do the layout:




I haven't run the traces. But they should be like the photograph above.

You can the PCB board made cheaply and you can get some edge mount SMA connectors from eBay.


Regards,
Jay_Diddy_B

[mark03]

4395A tops out at 500 MHz, so a TRL fixture like the first one pictured is probably not practical---it would be large and expensive.  But it is quite easy to build your own SOLT (short, open, load, thru) standards, and at 500 MHz they will be just as good as a commercial cal kit.  The hitch is that you may want to calibrate your VNA with a known (commercial) cal kit first, then measure and record your DIY version, so you can derive the coefficients to plug in to the 4395A matching your DIY kit.  If you search past threads in the RF forum here, this has been discussed pretty thoroughly.

Have fun!

[Jay_Diddy_B]

Hi mark03 and the group,

The idea was to suggest something to 'play' with a learn about VNA measurements. You can make the PCB very cheaply and you can enough to hack them up.

If I make the bold assumption that the propagation speed in FR4 is 0.7 times the speed of light.

If I assume that the difference in length between the thru calibration and the transmission line is 45mm. The 45mm Tline represents a 212 ps delay or a phase shift of about 38^o at 500 MHz.

The designer of the board has written 10 - 170^o at 120 MHz to 2 Ghz.
so about 40 ^o at 500 MHz.

I shared a design for a DIY Short, Open and Load in this thread:

Link: https://www.eevblog.com/forum/rf-microwave/diy-short-open-and-load-for-vna-calibration/

The PCB is one way to go if you don't want to do any metalwork.

Regards,
Jay_Diddy_B

[mark03]

You're right; I shouldn't have been as dismissive of the TRL board.  I actually made one for my 4396B which goes up to 1.8 GHz.  It was fun and worth doing as a learning exercise.  I tried two lines, the longer one about six inches in length, and it had some weird hiccups/resonances, possibly due to nearby structures on the board or the inferior process (a low-cost two-layer service).

Nonetheless, I think some homemade SOLT sets, both coaxial and on-PCB, would be more than adequate in this frequency range.  The HP app note "in-fixture measurements" is linked in one of the earlier threads and has a nice discussion of this.  BTW, you can make the coaxial standards from SMA board-edge connectors without any metal-smithing whatsoever.  All I used was a dremel to cut off the PCB-mounting legs.  The result should be sensibly perfect up to 500 MHz, or just about.  I don't even know if it's necessary to borrow a friend's cal kit; results might be perfectly adequate if you assume your DIY standards are perfect.

[AE7OO]

I have a couple of versions of the NanoVNA, both a "real" one from Huygens, and a cheap (about $30 delivered) one for learning on.

I  found https://www.amazon.com/Analyzer-Testboard-NanoVNA-F-NanoVNA-H-NanoVNA-H4/dp/B08B8QQCBS/ref=sr_1_11?dchild=1&keywords=nanovna&qid=1607386809&refinements=p_85%3A2470955011&rnid=2470954011&rps=1&sr=8-11 these on Amazon, however they are also available in from all the other sources.   

 


It was easy to turn this into a Open-Short-Through-Load calibration fixture.  Just add a decent 50 ohm resistor, it has everything else. 

And at less than $10, it has both cost and ease of convenience(aka laziness factor) going for it.