GPS Antenna selection

Hi,

I want to build a project that includes a gps module with an antenna. I'm not sure how to select the antenna.

The casing is made of aluminium (1.8 to 2.5mm thick). As i want to keep the device dust and moisture free, i would like to use a antenna inside the case, if that is possible.
Sadly i don't have much knowledge about gps so i hope that someone here can help me with my questions:

1.) Is it possible (at all) to use a gps antenna inside the closed aluminium enclosure. The front-panel is 1.8mm thick. If yes, what antenna should i choose?
2.) If it cant be used inside the enclosure, would it be possible to cut out a square in the front panel and put the antenna right in that square? Over the antenna there would be only the front panel foil (.9mm).
3.) If i need a antenna thats outside the device, are there any very small Antennas with SMA? (like 5-10mm long, not the 5cm long ones you know from wifi routers).

Thanks for your help.

1.) No, it isnt possible to put your antenna inside a metal box. On the other hand, it would make a lot of sense for you if your budget permits to use a plastic radome over your antenna to protect it from damage and your receiver from ESD.

The Taoglas antenna you linked to is a dual band antenna with an integrated LNA, designed for both GPS and GLONASS. Is that what you are looking for?

The square antenna needs to be outside any metal enclosed area, ideally on top, but its really designed for PCB placement. The Taoglas - and all patch antennas need to be facing upward or close to it.

Their most popular style is a square patch of (ideally silver plated) metal fed at a point slightly offset in a diagonal direction from its center, in such a way that it acquires right hand circular polarization.

The silver plated or plain metal patch is attached to a ceramic substrate picked for its dielectric properties, which make the patch much smaller than it would need to be with air but this also makes it much more narrow-banded (working over a narrower range of frequencies) and makes it more finicky about having a ground plane.

The Taoglas antenna you linked to is a compact one and its profile is higher (lower S/N ratio at the antenna, and IMHO, slightly higher chance of damage if its not protected inside of a plastic radome.)

It has an integrated low noise amplifier which means it requires a voltage to drive it.

One thing, though. Most modern GPS receivers are sensitive enough to not need an LNA unless the antenna is on the far end of a long piece of coax. Since your device is a one piece unit you dont need an LNA. Is your unit a multi-band receiver? If you don't know can you share what GPS module you plan to use? Multi-constellation GPS performs significantly better under some conditions. It all depends on what your application is, whether you need it.

The usual patch antenna is designed to work with a flat ground plane of at least 50-70 mm square and wont function properly without one.

A smaller patch antenna is likely to need one too, even though its smaller. A decent ground plane may be even more important if the actual patch is smaller.

The typical size of a ceramic patch antenna is around 25 mm square (not 10 mm square) and if you have the space for a larger square it will likely deliver significantly better performace. 10mm square is very very small for this kind of antenna. Thats why they need an LNA. Although taoglas is very much a reputable manufacturer and I am sure that antenna will work, the fact that its size has been so aggressively reduced implies tradeoffs. If you are able to go with the Sarantel antenna my gut feeling is I would consider that before getting an amplified 10 mm ceramic patch.

Unless your design both requires the antenna to be small and provides a significantly larger ground plane I would worry about the ground plane being inadequately sized. Ask them.

Note that the patch antenna absolutely requires both that a decent ground plane exist, the bigger the better, a smaller antenna may even be more dependent on a decent ground plane, and also all patch antennas start to lose their circular polarization at lower angles so they absolutely require that the antenna be pointed up within a range of at the most 15 or 25 degrees of vertical to work well. Also they should be in the clear without other antennas, or any other metal around them.

These kinds of situations all are the Sarantel antenna's strong points- major strong points- a QFH frees you from the orientation issue. Their implementation of it is unique in that its a fraction of the size of one without the high dielectric design they use. However its bandwidth is likely lower than the Taoglas.

Frankly, the bandwidth specified for that tiny Taoglas patch seems likely to either be overoptimistic or they manipulate it with filtration in the LNA. The LNA contains an SAW filter which is standard in many better GPS filters now. I just don't know. You should take what I am saying with the caveat that I am not an engineer, just a hobbyist who likes to fool around with GPS, especially antennas.

No, foil won't do, it would likely cause problems for the signal.

Most modern GPS receivers are a PCB which provides some ground plane area plus mounting for the antenna and they use a plastic case. Is there any reason you cant do that?

1.) No, it isnt possible to put your antenna inside a metal box. On the other hand, it would make a lot of sense for you if your budget permits to use a plastic radome over your antenna to protect it from damage and your receiver from ESD.The Taoglas antenna you linked to is a dual band antenna with an integrated LNA, designed for both GPS and GLONASS. Is that what you are looking for?The square antenna needs to be outside any metal enclosed area, ideally on top, but its really designed for PCB placement. The Taoglas - and all patch antennas need to be facing upward or close to it.Their most popular style is a square patch of (ideally silver plated) metal fed at a point slightly offset in a diagonal direction from its center, in such a way that it acquires right hand circular polarization.The silver plated or plain metal patch is attached to a ceramic substrate picked for its dielectric properties, which make the patch much smaller than it would need to be with air but this also makes it much more narrow-banded (working over a narrower range of frequencies) and makes it more finicky about having a ground plane.The Taoglas antenna you linked to is a compact one and its profile is higher (lower S/N ratio at the antenna, and IMHO, slightly higher chance of damage if its not protected inside of a plastic radome.)It has an integrated low noise amplifier which means it requires a voltage to drive it.One thing, though. Most modern GPS receivers are sensitive enough to not need an LNA unless the antenna is on the far end of a long piece of coax. Since your device is a one piece unit you dont need an LNA. Is your unit a multi-band receiver? If you don't know can you share what GPS module you plan to use? Multi-constellation GPS performs significantly better under some conditions. It all depends on what your application is, whether you need it.The usual patch antenna is designed to work with a flat ground plane of at least 50-70 mm square and wont function properly without one.A smaller patch antenna is likely to need one too, even though its smaller. A decent ground plane may be even more important if the actual patch is smaller.The typical size of a ceramic patch antenna is around 25 mm square (not 10 mm square) and if you have the space for a larger square it will likely deliver significantly better performace. 10mm square is very very small for this kind of antenna. Thats why they need an LNA. Although taoglas is very much a reputable manufacturer and I am sure that antenna will work, the fact that its size has been so aggressively reduced implies tradeoffs. If you are able to go with the Sarantel antenna my gut feeling is I would consider that before getting an amplified 10 mm ceramic patch.Unless your design both requires the antenna to be small and provides a significantly larger ground plane I would worry about the ground plane being inadequately sized. Ask them.Note that the patch antenna absolutely requires both that a decent ground plane exist, the bigger the better, a smaller antenna may even be more dependent on a decent ground plane, and also all patch antennas start to lose their circular polarization at lower angles so they absolutely require that the antenna be pointed up within a range of at the most 15 or 25 degrees of vertical to work well. Also they should be in the clear without other antennas, or any other metal around them.These kinds of situations all are the Sarantel antenna's strong points- major strong points- a QFH frees you from the orientation issue. Their implementation of it is unique in that its a fraction of the size of one without the high dielectric design they use. However its bandwidth is likely lower than the Taoglas.Frankly, the bandwidth specified for that tiny Taoglas patch seems likely to either be overoptimistic or they manipulate it with filtration in the LNA. The LNA contains an SAW filter which is standard in many better GPS filters now. I just don't know. You should take what I am saying with the caveat that I am not an engineer, just a hobbyist who likes to fool around with GPS, especially antennas.No, foil won't do, it would likely cause problems for the signal.Most modern GPS receivers are a PCB which provides some ground plane area plus mounting for the antenna and they use a plastic case. Is there any reason you cant do that?

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They grab their ephemeris from the network even if there is no sim card. So it can still send an e911 location info if you make an emergency call which doesnt need a sim card. The reason a standalone, non networked GPS takes so long is it needs to download a table of expected orbital data into memory to work properly. That takes around 15 minutes.

People in North Korea using the Chinese cell network learned (this info is probably outdated) that if they kept their Chinese cell without its batteries in it, and then just put the batteries in and quickly called relatives in South Korea and then hung up right away, and removed the batteries, the old system the MSS had often could not locate people to be taken away to concentration camps. A few years ago they got a much more modern system to track down illegal cellphone users that works I suspect on TDOA, and its accurate to just a few meters. In this country where people are literally starving the government had stopping illegal international calling as their top priority, so they bought a system built its rumored by Rhode and Schwarz, which must have been sold to them by some 3rd party dealer, because of sanctions. Now all their cell phones, probably just like other countries, send their GPS locations, probably right away, due to AGPS. So they have multiple, redundant systems for locating illegal users of foreign networks in their border areas.

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A cell has access to the network so they now use AGPS, which basically means fetch the ephemeris over the network enabling an almost instant start.

If you dont pay for a data plan it still gets the ephemeris data and your GPS's location data is available to everybody else but you.

Will it fall back to downloading the ephemeris from the satellites when its not in range of a cell network? I don't know but I kind of doubt it. So dont count on using a cell GPS is you are a hiker, becuse as soon as you are over the hill from a cell site the GPS may stop working, (if the cant fall back to using the actual satellite ephemeris) either right away or in a day or two when the ephemeris data gets stale.

There should be a law requiring that GPSs natural functioning not be disabled for use by users by greedy cell companies.


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Yesterday I was surfing for some other reason and I noticed that Molex now sells compact helical GPS antennas. I dont know if they are QFH but it seems that they might be, if so they may be more likely to operate properly independently of any ground plane.

Sarantel used to make very good - very copact (tiny) ones but I remember hearing they are no longer in business. They are worth hunting down and using if you can find one.  But even if you can find one now it might be hard to find them in the future.

Similarly, if this is for a hobby use maybe you could find an old Vaisala aerosonde (QFH) GPS antenna. If you really want an GPS antenna that will work in almost any orientation, thats what I would pick. They are a full sized QFH for GPS which means two interwoven helical loops with a height or around 8 cm which fit in a cylinder with a diameter of around 3 cm.

If you are looking for more details, kindly visit GNSS Antenna.