GPS trace antenna - Page 1
Forum section: electronics / rf-microwave

author: tszaboo
author_rank: Super Contributor
timestamp: March 14, 2023, 03:24:45 pm
content: Hi. I have a question for the RF magicians. What is the reason, that we don't see products with GPS PCB trace antennas? This is used widely for 2.4GHz applications, and I myself was able to follow reference designs and build good functioning products with inverted F antennas. But when I look for the same topic with GPS, nothing. Find lots of ceramic patch antennas, that are big, and expensive.My theory is, if I size a F or PIFA antenna for that 1.5GHz band that GPS is using, connect the VNA to it, match it, and if it's good for transmission, surely it's good for reception, right? Or am I completely wrong about this?

author: SeanB
author_rank: Super Contributor
timestamp: March 14, 2023, 08:07:51 pm
content: Because the ceramic antenna combines the first stage of filtering, giving a very high Q and very good out of band rejection in a single unit, allowing the GPS to get a lot of selectivity before the high gain stage, so it is hard to saturate. Remember GPS is recovered out of the receiver noise floor by correlation, the signal strength is normally so low it is barely detectable above the receiver noise floor.

author: tszaboo
author_rank: Super Contributor
timestamp: March 15, 2023, 09:11:33 am
content: So wouldn't a SAW filter after a regular antenna have the effect. I'm aware of the miniscule amounts of received signal strength of the GPS signal. Hence the LNAs and other techniques to increase the signal strength.I cannot really use ceramic patch antennas, because the PCB is mounted vertically, and these have high directionality perpendicular the PCB, so they would receive horizontally, not ideal.https://www.hindawi.com/journals/ijmst/2008/287627/Found an article with a PCB printed patch antenna. What I noticed is that they are talking about -36dB on the S11 parameters beingsufficientfor the GPS purposes, so and indeed the antenna has a very high Q.https://content.u-blox.com/sites/default/files/products/documents/GNSS-Antennas_AppNote_%28UBX-15030289%29.pdfUblox also mentioned PCB antennas in their app note on page 11, but also saying "PCB antennas are not recommended for use in devices where navigation is an essential feature." so I have to assume that the overall effectiveness of such an antenna is not great.

author: samofab
author_rank: Regular Contributor
timestamp: March 15, 2023, 09:41:17 am
content: Consider using Ignion NN03-320 antenna (no affiliation)

author: tomnut
author_rank: Newbie
timestamp: March 19, 2023, 07:09:50 am
content: Fair comments about the filtering, but surely a SAW will fix that.How big is the GPS antenna in your phone? Surely it is an IFA and not a 11x11x5 mm circularly polarised patch...The qrp-labs balloon trackers have a bit of wire for a dipole GPS antenna. I suppose they use a GPS module that includes an LNA.Fromhttps://qrp-labs.com/u4b.html"The GPS antenna can be made of simple #28 (0.3mm) enameled wire; a 1/4-wave at 1575Mhz is about 45mm. The feedline consists of 1-inch of twisted wire, about 6 turns works well."The smallest linear ceramic or PCB GPS antennas are probably IFAs anyway. So I'd say try one and see how it works. It might end up being larger than the various ceramic patches or linear antennas.So I'd say try an