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Reference Guide Winner
Comments: Hi Joel, Thanks for the info. Couple of questions. What are some of the key technical considerations to be thinking of when purchasing a network analyzer? which models are best for which appplications? Do most VNA today support differential s-parameters? if so what format is that data in. Is it directly compatible with simulation data inputs like Touchstone? thanks. Page Page Hurstberg, JTP Inc.
3/28/2008 1:41:00 PM
Response from the Author: One of the key specs that is often overlooked is Receiver Linearity, sometimes called "Dynamic Accuracy" which describes how well a receiver measures different power levels. This is really important in cases where the DUT changes the power (almost always). Sometimes this can be derived from the compression point of the VNA recevier, which we typically target at 0.1 dB. I can't speak for other vendors, but in the Agilent portfolio we have the ENA series which includes the ENA and ENA-L, and we have the PNA series which includes the PNA, PNA-L and the new PNA-X. ENAs are limited to RF frequencies (below 8.5 GHz), and are used primarily for S-parameter measurments. They are compact and lower cost, but a bit less flexible than the PNA-series. The PNA has more capability, particularly the PNA-X series, which includes dual sources, built-in combiners, and a flexible test set architecture which makes it easy to couple in other instruments. This is really useful for active devices measurments and non-linear measurements. As far as I know, all 4 port analyzers have some support for differential S-parameters. ENA supports "mixed-mode" S-parameters computed from single-ended measurements. PNA supports "true-mode" differential measurents. The outputs are in typically single-ended outputs in touchstone S4P files, which ADS knows how to read (there is no standard file defined for differential S-parameters, but we're working with a well known standard committee to try to get one defined). To use this you just drop a 4 port S-parameter block down, and read it in. We can also directly output the differential parameters in "citi-file" which ADS can also read, but doesn't understand that the data is differential (that is ADS doesn't have an differential S-parameter input block). But you can look at the data in the display page. We also save a version called ".prn" which is a comma separated data file that can be imported easily into Excel.
Reference Guide Winner
Comments: Joel, Thank you for the interesting article. I need a clarification: you say that old VNAs used samplers rich of harmonics, while in this case we have a separate LO. I suppose this is similar to the 8714 (low-end model) where, if I remember well, we have input mixers with low-if output (LO is tracked at a few kHz from RF). Is this the same for PNAx or we have a higher IF? I say this because I see problems in handling non-linear devices, because we don't have image-reject filters at all in a VNA and we may have unwanted components easily converted by the mixer. How is this managed for handling nonlinear measurements? Best regards, Roberto Roberto Visentin, Saipem Energy Services,
4/2/2008 7:26:32 AM
Response from the Author: We have a few ways to handle these issues. In the PNA-X we have a digital second converter with flexible IF (between about 0.1 MHz and 15 MHz) so it is possible to "dodge" spurious signals if we know where to expect them. We use this technique in the Scalar Mixer Calibration to dodge images of the LO. In this mode, we move the LO and the IF, on a per-point basis, to avoid spurs. We can also do this in IMD measurments, for the same reasons.
Reference Guide Winner
Comments: Hi Joel...very informative article. Just one question, how did this new VNA hadle the large signal measurement such as IMD, can u elaborate more on this? Thanks Syuhaimi Syuhaimi kassim, Avago Technologies
4/2/2008 11:00:31 PM
Response from the Author: For IMD measurements, in the PNA-X we can use both sources, and the internal comibine to generate a two tone response. Our receiver is quite linear, and has a built in step attenuator so we can possition the power to allow a very good measurement of the IM tones and produces, and we can de-couple the sources from the receivers so we can track any harmonic or IM product from the DUT. With this flexibiltiy you can do such things as sweep the sources power while the receiver measures the IM3 tone, to create a swept power IM plot. We can also use the equation editor to compute other factors like the intercept point, IP3.
Reference Guide Winner
Comments: How much of an error would be expect by calibrating the VNA using a ISS and making measurements on silicon, especially for passive components? Is this error frequency dependent? Amit Bavisi, Freescale Semiconductor
4/10/2008 1:39:16 PM
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The modern age of Vector Network Analyzers (VNA) started with the introduction of the HP 8510, in 1984. This was the first, fully integrated, fully automated VNA, and was the gold-standard for measurement instruments.