Eric Bogatin, Signal Integrity Journal Technical Editor
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Eric Bogatin is Technical Editor at Signal Integrity Journal and the Dean of the Teledyne LeCroy Signal Integrity Academy. Additionally, he is an Adjunct Professor at the University of Colorado - Boulder in the ECEE Dept. Eric improves the signal to noise ratio by sorting through all of the information available and finding the best quality content to publish on

Signal Integrity

I Kissed a Lot of Frogs Lately, So You Don’t Have To

November 10, 2020

With more than three times more webinars offered in our Covid-19 era, we have more opportunities to accelerate up the learning curve or waste a lot of time. I sacrificed hours of my time watching dozens of webinars to identify these three princes. Check them out. They are well worth your time.

RF Microwave Signal Chain and Network Analysis by Tony Wade, Keysight.

This is really the first of a series of five webinars in Keysight’s Back to Basics series. This link will take you to all five webinars in the series. It first aired in July but is available on-demand.

True confession. When I got started with VNA measurements 35 years ago, I got my jump start by visiting the local Hewlett Packard applications lab and sat down next to Tony Wade who, at the time, was a new application engineer and expert with the HP8510.  With remarkable patience, he walked me through S-parameter measurements with his HP8510.  Tony is still at it, teaching engineers why S-parameters are so useful and how to get started using network analyzers.

I learned most of what I know about network analyzers and S-parameters from sitting next to Tony Wade and having him tell me his stories.

In this webinar, he introduces a new generation of engineers to the modern network analyzer. They have come a long way from the 8510 days. As he says, “Once you measure the S-parameters of a device under test, you know absolutely everything to know about the device.” Figure 1 is an example of some of the information he describes you can get with a network analyzer.


Figure 1.   Examples of some of the terms a VNA can measure.

If you are new to network analyzer measurements, you will experience the same excitement about the power of the network analyzer as I was infected when I sat next to Tony for the first time. The only difference is he has many more stories to share about why you should also fall in love in VNA instruments and measurements.

PCB Material Characterization with One Measurement by Jason Ellison and Michael Rowlands, Amphenol

This webinar is part of DesignCon’s Back to School webinar series.

Everyone cares about the dielectric constant and losses of the laminates they use in high-speed applications. If we have two different line lengths, there are many methods available, such as Intel’s delta L method or the IEEE S370 impedance corrected 2x thru de-embedding process, to get the S-parameters of a single, uniform differential pair.

Once we have the S-parameters for the uniform line section, we can use a few simple algorithms to extract the Dk, the Df and some terms related to the copper loss. But what if you don't have two lines on your test board? What if you just have one line, the test line? How do you get the Dk and Df values?

Jason and Michael came up with a simple process to get the same level of accuracy in extracting material properties using just one line. The key is to have some knowledge of the launch geometry and use a free de-embedding tool available from AICC. This free tool allows them to de-embed the uniform part of the transmission line after removing the coax launch fixture.

Once they have the uniform line S-parameters and the physical length, they extract the Dk from the phase of the insertion loss and the total loss from the insertion loss. From the insertion loss data, they fit a simple polynomial expansion of the loss vs frequency to extract the dielectric loss term, the smooth copper loss term and the roughness term. They use an HFSS simulation to account for the expected smooth copper behavior. Figure 2 shows their algorithm.


Figure 2. Algorithm to use a polynomial expansion to fit the conductor and dielectric losses.

If you care about high frequency laminate properties, this is a very clever technique well worth checking out. Their algorithm from separating conductor and dielectric loss including the roughness impact is well illustrated.

Which Material Properties have the most impact in High Speed Digital Applications by John Coonrod, Rogers Corp.

Rogers Corp has a wealth of valuable experience using their materials in high-frequency applications. Over the years, their experts, like Al Horne and John Coonrod, have shared much of what they have learned with the rest of us. Do not pass up an opportunity to listen to either of these experts.

In this webinar, John shares basic and advanced properties of materials every high-speed engineer should know. He emphasizes that it is not just intrinsic material properties that influence the electrical performance of transmission lines composed of these materials. For example, the skew from glass weave depends not only on the glass weave properties of the laminate but also the pitch of the lines in the differential pairs.

The surface roughness of the copper influences the Dk of the laminate. This means it is more difficult to extract the intrinsic Dk of a laminate unless the surface roughness is taken into account. The rougher the copper, the higher the effective phase delay for a propagating signal and the higher effective Dk.

In addition, for the same roughness of copper, the thickness of the laminate layer also influences the effective Dk. The thinner the laminate, the larger the influence the copper roughness has on the phase delay of a signal. Figure 3 shows this influence on stripline structures. Thinner layers show higher Dk.


Figure 3. Impact on the thickness of stripline layers with the same material and the same roughness copper.

Among the wealth of information John presents in this webinar, is one plot, he shows in passing which I think should get more attention in the industry. I first saw this in a presentation from Al Horne and I am still astonished every time I see it. Figure 4 shows the measured insertion loss of two microstrip lines, of exactly the same width and length on exactly the same low loss substrate material. Most of the loss in this example is conductor loss.


Figure 4.  Insertion loss of two nominally identical microstrips, one with rolled copper and one with ED copper.

I find it remarkable that rolled copper has such a smooth surface and contributes such a small amount of additional roughness loss compared with ED copper. With so much attention these days on coming up with magical chemical potions that enable smoother electro deposited (ED) copper, we should not loose sight of the properties of rolled copper which has been available for more than 50 years.

Check out these three valuable princes among the frogs I kissed. You’re welcome.


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