Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

RF probe for network analyzer measurements

RF probe for network analyzer measurements

RF probe for network analyzer measurements


I´m working with small RF amplifiers designed for production. That means that when I have to take lab measurements of intermediate stages, where there are no cables, I have to solder on the PCB coax cables all the time. I was wondering if anybody could advise me on RF probes or something similar to a probe which I can connect to the network analyzer so I can put the signal at any PCB point without soldering a cable. (like an osciloscope probe but for a network analyzer)

Thanks a lot.

RE: RF probe for network analyzer measurements

This is a common and difficult problem, especially difficult in the GHz range. It is nice to have packaged amplifiers with SMA or K connectors so you get well defined input and outputs.

If you just solder on a coax you have added another 50 ohms in shunt at that point in the circuit. If you disconnect the load so you only have one 50 ohm load you then have an open circuit stub driving the open pads and you have changed the load conditions on the amplifier under test. What you want is a coplanar waveguide output so you can make signal and ground connections easily to the amplifier. If nothing else you should be able to get a repeatable measurement, although the absolute accuracy is questionable.

You can get wafer probe stations for microwave circuits. Take a look at those for clues.

RE: RF probe for network analyzer measurements

If you need to test each stage for some reason in production, then you should design in some sort of test point for doing that.  A 20 dB directional coupler in microstrip with the coupled port attached to some sort of gpo (snap fit) surface mount connector would do as a probe point.

You turn on the amplifier chain, and you can probe the output power of each stage, minus the 20 dB coupling.

RE: RF probe for network analyzer measurements

It might be possible to design some sort of loosly coupled air-line directional coupler in a test fixture to lower near to the amplifier PCB.  You would have some sort of coupling line approximately quarterwave long, and lower it close to the microstrip line at the output of each amplifier stage.  If you lowered it only close enough to get maybe 25 db down coupling, it would not seriously impact the interstage tuning.  Probably an air gap of maybe 3 substrate thicknesses or so?

Of course, You would have to carefully calibrate it somehow to make sense of the data.  Also, you would need some straight lines interstage to mate up with the coupled section.

RE: RF probe for network analyzer measurements

What's your frequency range?
Common is a 3 point probe, it requires you to bring up ground points on both sides of your microstrip line. The 3 pint probe grounds touch these points and the center of the probe is on your transmission line.
At higher frequencies, you need to break your line, test your items, then solder the lines back together.

You could just add the grounds and make measurements on a good unit and record the data as a standard, then compare to the standard.

Tricky measurement if you're winging it. Hard to get the pass fail requirements with the probe some times.


Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close