Checking Cable Performance with VNA


Reading time ( words)

In my December 2013 column Comparing Cable Shields,we showed that poor cable shields can result in significant noise pickup from the air, which can easily mask a few mV of noise voltage that we need to measure on a good power distribution rail. We showed a quick comparison of cable shield quality with a signal source and an oscilloscope. In this column, we will look at the same cables in the frequency domain, using a pocket-size vector network analyzer (VNA).

Vector network analyzers are similar to time domain reflectometry (TDR) instruments that many digital engineers may be more familiar with: They both transmit a known signal into the device under test (DUT) and measure the response. TDR instruments use a step waveform with a given rise time; VNAs use a sine wave source sweeping the frequency within a user-defined range. VNAs have long been popular in microwave engineering and more recently in high-speed digital engineering. They measure what are called scattering (S) parameters, which are the complex ratios of transmitted and reflected waves.

In recent years, small, low-cost, portable VNAs have become available. Measured data in this column was collected with a miniVNA Pro, a pocket-sized VNA. It operates over the 0. –200 MHz frequency range. It is battery-powered and features USB and Bluetooth connectivity (Figure 1). We hooked up a two-port DUT to the DUT and DET SMA connectors. The instrument injects sine waves (swept from 0.1–200 MHz or in any user-defined sub-band of it) into the cable connected to the SMA labeled DUT, measures sine waves propagating back from the DUT SMA (reflection) and the DET SMA (transmission), and compares the measured received sine waves to the injected sine waves to characterize reflection (e.g., S11) and transmission (e.g., S21). With this instrument, we can measure the full S matrix of a two-port DUT, though to get the full matrix, we have to manually set up four independent measurements. The instrument comes with open, load and short SMA calibration standards, shown on the lower left in Figure 1.

Read the full column here.


Editor's Note: This column originally appeared in the March 2014 issue of The PCB Design Magazine.

Share




Suggested Items

Polar Instruments: Simulating PCB Potentialities

12/08/2022 | Nolan Johnson, I-Connect007
Nolan Johnson checks in with Polar’s Martyn Gaudion on the evolving needs of global PCB manufacturing markets in a post-pandemic world, where generating accurate PCB specification documentation is essential to successfully navigating today's rampant supply chain constraints. Polar has positioned itself to meet these needs through agile software product developments that allow OEMs and fabricators to simulate material interactions and end-product specifications, including in-demand features like a comprehensive "structure view" that allows users to visualize all the transmission lines on a given a PCB. Though keeping pace with the demands of a rapidly growing industry has been challenging, Polar's commitment to innovation has kept its software suite ahead of the curve.

HyperLynx: There’s an App for That

08/05/2022 | I-Connect007 Editorial Team
I recently spoke with Todd Westerhoff, product marketing manager for signal integrity software tools at Siemens. We discussed a new capability called HyperLynx Apps that offers a new take on traditional signal and power integrity analysis, and how that fits in with the Siemens plan to put SI and PI tools into the hands of more designers early in the design cycle.

Webinar Review: Thermal Integrity of High-Performance PCB Design

08/01/2022 | Andy Shaughnessy, Design007 Magazine
Electrical and mechanical engineers may be working on the same product development teams, but they speak different languages, and they have completely different objectives. As a result, these folks almost never use the same software tools. But Cadence’s new Celsius Thermal Solver is an exception to the rule. In a new CadenceTECHTALK webinar, “How Static and Dynamic IR Drop Analysis Can Help PCB Designs and Challenges,” product manager Melika Roshandell and SerDes SI/PI engineer Karthik Mahesh Rao explain how the EE and ME can both use the Celsius Thermal Solver to achieve their disparate objectives.



Copyright © 2023 I-Connect007 | IPC Publishing Group Inc. All rights reserved.