Antenna Measurement with the R&S FPC1500 Vector Network Analyzer

RE: Antenna Measurement with the R&S FPC1500 Vector Network Analyzer

dc2daylight — Tue, 16 Mar 2021 02:15:30 GMT

I realize this is an old thread but I enjoyed the article. I am planning an FPC-1500 purchase soon and also have a third party OSL with unknown coefficients. I am in the U.S. Can anyone tell me where to I might send it for evaluation so I can get the values needed to enter into InstrumentView? Thank you!

RE: Antenna Measurement with the R&S FPC1500 Vector Network Analyzer

jc2048 — Mon, 20 Aug 2018 14:10:45 GMT

This is really good - thanks for posting it.

The readings for the second marker are RELATIVE to the first, aren't they? I was a bit puzzled by the low resistance given the placement of the marker but, if I'm now understanding it correctly, it's actually at about 64 ohms (real part) ie the sum of the two.

That aerial is a log-periodic, isn't it. They're used a lot for (higher frequency) emc work because of the very wide bandwidth. I've often wondered what the actual response would look like. We had one with larger dimensions (not a pcb, obviously, but physical rods) for the range 300MHz to 1GHz (below 300MHz we used a bi-conical). It's surprisingly good given that the vast width of the response is coming from the separate elements being summed together - I would certainly have expected it to be a bit up and down, because of the tendency for the elements to interact (they kind of act like the reflectors/directors of a Yagi to each other in a very complex way - how in earth you design one I don't understand - perhaps you start at the low frequency end and optimise as best you can as you work your way along adding the elements), but would have expected it to be more extreme than this. For emc use it was fine because it was characterised with the test receiver to give a level overall response for the measurements.

I've never been too clear how directional it is - back then we treated it like a Yagi (ie just pointed it directly at the EUT) but maybe that isn't the case.

I don't know a lot about rf, but I wouldn't have thought it would be too good for a transmitting aerial because of that drop down close to 25 ohms (it wouldn't necessarily be very comfortable for a power amplifier designed for 50 ohms to drive that), but then where would you want to use a wideband aerial for transmitting (other than, maybe, in a test situation).

RE: Antenna Measurement with the R&S FPC1500 Vector Network Analyzer

shabaz — Mon, 20 Aug 2018 14:04:43 GMT

It's also worth mentioning, that although I used the FPC1500 here, the tests are achievable with other hardware - it's just more effort to set up. The first two charts are achievable with a spectrum analyzer, bridge or coupler, and any signal source (tracking generator or sig-gen or even a dev-board for an RF transmitter/transceiver could be used).

The spectrum analyzer could be replaced with an SDR in theory. So basically for a couple of hundred $ it's feasible.

For lab use you'd want to use a VNA though.

There is a similar-ish thing discussed here:

https://www.rtl-sdr.com/rtl-sdr-tutorial-measuring-filter-characteristics-and-antenna-vswr-with-an-rtl-sdr-and-noise-sou…

although they went with a noise source, and they're using an RTL-SDR device which isn't capable of 2.4GHz operation - but the concept is the same.

RE: Antenna Measurement with the R&S FPC1500 Vector Network Analyzer

colporteur — Mon, 20 Aug 2018 12:27:02 GMT

I almost weeped reading your commentary. My electronics career took a fork in the road to computers away from RF some 18 years ago. I still recall printing time domain reflectometer (TDR) patterns for the ten odd VHF and UHF antennas we stocked.

I took acceptation to your suggestion "the signal travels with virtually no loss over a cable (often a coax cable). If I recall correctly cable and the associated connectors had loss factors used to calculate the power arriving at the antenna. Has the technology changed to make a statement true today?

None the less great piece. In the era of tubes we didn't have the wonderful technology described and displayed in your article. Thanks for sharing so I could take a trip down memory lane.

Sean