Re: [time-nuts] GNSS Antennas (was: Rooftop antenna and splitter)
Hi I get the impression that they do indeed run things up a band at a time and pretty much ignore what is in-between. Again, we’re talking about the “affordable” end of the new antenna range here and not the price is no object part of the market. Bob > On Jan 31, 2019, at 12:45 PM, Attila Kinali wrote: > > On Thu, 31 Jan 2019 08:51:46 -0500 > Bob kb8tq wrote: > >> Looking at network analyzer sweeps, it becomes pretty apparent that whatever >> combination of things are involved, they only work inside each of the target >> sub-bands. >> Once you get to the edge, it all falls apart. It comes back together once >> you get to >> the edge of the next sub-band. Some of that is intentional filtering so >> sorting it out >> that way … not so much. > > Transmission line phase shifters are pretty narrow band. > Getting them to 5% bandwidth with reasonable phase and > amplitude stability is already not straight forward. But > for a combined GPS/Galileo/Glonass L1/L2/L5 antenna, > a bandwidth of over 30% would be needed. Not an easy task > at all. Making them work for a few select bands is a lot > easier, if still a bit non-standard. At least EM simulation > tools help a lot with that. > > Attila Kinali > > -- > It is upon moral qualities that a society is ultimately founded. All > the prosperity and technological sophistication in the world is of no > use without that foundation. > -- Miss Matheson, The Diamond Age, Neal Stephenson > > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] GNSS Antennas (was: Rooftop antenna and splitter)
On Thu, 31 Jan 2019 08:51:46 -0500 Bob kb8tq wrote: > Looking at network analyzer sweeps, it becomes pretty apparent that whatever > combination of things are involved, they only work inside each of the target > sub-bands. > Once you get to the edge, it all falls apart. It comes back together once you > get to > the edge of the next sub-band. Some of that is intentional filtering so > sorting it out > that way … not so much. Transmission line phase shifters are pretty narrow band. Getting them to 5% bandwidth with reasonable phase and amplitude stability is already not straight forward. But for a combined GPS/Galileo/Glonass L1/L2/L5 antenna, a bandwidth of over 30% would be needed. Not an easy task at all. Making them work for a few select bands is a lot easier, if still a bit non-standard. At least EM simulation tools help a lot with that. Attila Kinali -- It is upon moral qualities that a society is ultimately founded. All the prosperity and technological sophistication in the world is of no use without that foundation. -- Miss Matheson, The Diamond Age, Neal Stephenson ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] GNSS Antennas (was: Rooftop antenna and splitter)
On Wed, 30 Jan 2019 20:33:23 -0800 Peter Monta wrote: > Mini-Circuits has such a 4-port phase splitter, part number SCQ-4-1650+. > It's $25, which is not super cheap, but it's unclear one could implement > such a network with a planar circuit for less, and the planar circuit would > be more bulky. That one looks interesting indeed. Especially as the datasheet mentiones quadrifilar. Now I wonder whether that means the internal structure is a quadirfilar transformer or it is meant for quadiriflar antennas. While the latter would be a weird way to describe it, the former sounds more plausible. But then, I have no idea how one could use a quadrifilar transformer for a polyphase splitter. Does someone have an idea? Attila Kinali -- It is upon moral qualities that a society is ultimately founded. All the prosperity and technological sophistication in the world is of no use without that foundation. -- Miss Matheson, The Diamond Age, Neal Stephenson ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] GNSS Antennas (was: Rooftop antenna and splitter)
Hi If you take a hammer to one of these antennas, they seem to mostly play games with transmission lines on pc boards. The number of components involved is pretty small. If hammering one apart does not sound like a great thing to do, there are pictures here and there. I have yet to see a picture that shows enough to actually make sense out of. I’d bet that is intentional. Looking at network analyzer sweeps, it becomes pretty apparent that whatever combination of things are involved, they only work inside each of the target sub-bands. Once you get to the edge, it all falls apart. It comes back together once you get to the edge of the next sub-band. Some of that is intentional filtering so sorting it out that way … not so much. Bob > On Jan 30, 2019, at 11:33 PM, Peter Monta wrote: > > Hi Attila, > > > The "good" patch antennas thus >> employ a four point feed, but this makes the whole antenna quite a >> bit more expensive, as a 0°/90°/180°/270° phase spliter/hybrid is >> needed. Of course, any such circuit is rather difficult to make >> wide-band and thus becomes the bandwidth limiting element. >> > > Mini-Circuits has such a 4-port phase splitter, part number SCQ-4-1650+. > It's $25, which is not super cheap, but it's unclear one could implement > such a network with a planar circuit for less, and the planar circuit would > be more bulky. I've been thinking of picking up one of these to give an > untuned 4-filar helix a try (not a fancy resonant backfire quadrifilar > helix, which are hard to make broadband, but just a plain set of 4 helices > and the combiner). > > From the data sheet it's clear they have GNSS in mind, and it is quite > broadband: > > https://www.minicircuits.com/pdfs/SCQ-4-1650+.pdf > > Cheers, > Peter > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] GNSS Antennas (was: Rooftop antenna and splitter)
Hi Attila, The "good" patch antennas thus > employ a four point feed, but this makes the whole antenna quite a > bit more expensive, as a 0°/90°/180°/270° phase spliter/hybrid is > needed. Of course, any such circuit is rather difficult to make > wide-band and thus becomes the bandwidth limiting element. > Mini-Circuits has such a 4-port phase splitter, part number SCQ-4-1650+. It's $25, which is not super cheap, but it's unclear one could implement such a network with a planar circuit for less, and the planar circuit would be more bulky. I've been thinking of picking up one of these to give an untuned 4-filar helix a try (not a fancy resonant backfire quadrifilar helix, which are hard to make broadband, but just a plain set of 4 helices and the combiner). From the data sheet it's clear they have GNSS in mind, and it is quite broadband: https://www.minicircuits.com/pdfs/SCQ-4-1650+.pdf Cheers, Peter ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
[time-nuts] GNSS Antennas (was: Rooftop antenna and splitter)
On Sun, 27 Jan 2019 14:24:52 + Bill Slade wrote: > The very best GNSS antennas tend to be based on suspended patch antenna > (air-dielectric) structures because they give the best > bandwidth/radiation efficiency (and hence, noise temperature) > performance. While it is true that air-patch antennas give good bandwidth and radiation efficiency, they are not really ideal antennas for GNSS applications. The main drawback is their quite high Q, which results in high group delay variation. Another annoyance is that patch antennas form wave guides between the radiating element at the top and the ground plane at the bottom. This leads to radiation out at the sides and thus increased side and backlobes, which in turn limit both multipath surpression and the axial ratio (ie the ratio between RHCP and LHCP radiation) The cheap patch antennas also employ only a single feed-point, which, due its asymmetry, leads to non-uniform radiation and phase patterns (aka movements of the phase center). The "good" patch antennas thus employ a four point feed, but this makes the whole antenna quite a bit more expensive, as a 0°/90°/180°/270° phase spliter/hybrid is needed. Of course, any such circuit is rather difficult to make wide-band and thus becomes the bandwidth limiting element. Of the common geodetic class antennas I am aware of, only the Trimble Zephyr is a patch antenna[1], but with an rather complex n-point feed. The Novatel PinWheel[2,3] is a variation of the archimedian spiral antenna. Most of the single frequency geodetic GPS antennas are, AFAIK, crossed dipoles, often combined with a electromagnetic bandgap (e.g. choke rings) to increase impedance towards low and negative elevations. I have seen bow-tie antennas as well, but I do not know how common these are. The jury is still out on what the best antenna structure for geodetic work is, but it seems that it is more an issue of how much money someone spends on optimizing the non-ideal behaviour than a fundamental issue of the structure itself. For more information on GNSS antennas, I recommend the book by Rao et al. [4]. It's quite expensive if you buy it normally, but Artech has some sale every half year. If you wait for the right one you can get the book for 30-50% less. Attila Kinali [1] "The Design and Performance of the Zephyr Geodetic Antenna", by Krantz, Riley, Large, 2001 https://kb.unavco.org/kb/file.php?id=135 [2] "A Novel GPS Survey Antenna", by Waldemar Kunysz, 2000 http://meridware.com.tw/NOVATEL/Documents/Papers/gps600antenna.pdf [3] "High Performance GPS Pinwheel Antenna", by Waldemar Kunysz, 2000 http://webone.novatel.ca/assets/Documents/Papers/gps_pinwheel_ant.pdf [4] "GPS/GNSS Antennas", by Rao, Kunysz, Fante, McDonald, 2013 -- The bad part of Zurich is where the degenerates throw DARK chocolate at you. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
