Looking for info on 25mm GPS ceramic patch antennas

[billdz]

Most of my GPS trackers have a 25mm square ceramic patch antenna with a pin through the middle (slightly off center) that is soldered to the circuit board (see pic). My understanding is that the ceramic exterior is just to flatten and protect a wire antenna inside. Is anyone familiar with these antennas?

One of my devices recently has been intermittently losing the GPS signal. I opened the tracker and saw a crack in the antenna. Apparently this is adversely affecting reception. I see similar antennas for sale on eBay for around $5, not sure whether they are interchangeable with mine. I am guessing that replacement involves simply unsoldering the pin, removing the old antenna, placing the new antenna in the same spot and soldering the pin. Is that right?

Anyone had a similar issue or have any thoughts on how to repair or replace the antenna?

Thanks,
Bill

 

[RFMan]

That is a microstrip patch antenna; the ceramic is the dielectric. There is no wire inside. Roughly speaking, the metal patch and the ground plane, with dielectric in between, form a resonant cavity. It is small due to the high dielectric constant of the ceramic. The fringing electric field at two of the edges is equivalent to two magnetic dipoles, which radiate or receive. The antenna is circularly polarized to receive GPS signals.

You should be able to replace it, depending on the details of how it is attached (if the ceramic is bonded to the ground plane, it is more difficult).

It must have gotten a pretty good lick to crack.

 

[cerving]

Be very careful when you're unsoldering that center pin, you don't want to damage the pad that it goes into. A vacuum desoldering tool is your best bet. Those antennas have a conductive tape on the bottom that attaches to a ground plane, probably on the PC board, so you should be able to pry it off once the center pin is unsoldered.

 

[billdz]

OK, thanks for the info, sounds like a project. So the metal foil on top of the ceramic is the driven element and the foil on the board is the ground plane, interesting. How does the antenna get circularly polarized?

 

[UhClem]

The patch is 1/2 wave long which is the key. In a linear patch just two edges (opposite each other of course) radiate. (the slot between the edge and ground plane) By changing the width you change the input impedance.

For circular polarization you want to also get the other pair of edges involved, but with a 90 degree phase shift. Fiddling with the feed point and other tricks do that. (Locating the feed point away from the edge lowers the input impedance as well.)

The antenna inputs of GPS receivers are very ESD sensitive so you should use ESD precautions when handling the antenna.

 

[billdz]

What are ESD precautions?

 

[OverTheTop]

Taoglas is a popular brand I think. Digikey probably have them.

https://www.taoglas.com/product-cat...s-antennas/internal-gps-active-patch-modules/

 

[Titan II]

What are ESD precautions?

https://www.google.com/search?q=esd...hrome.0.0l6.1215j0j4&sourceid=chrome&ie=UTF-8

 

[billdz]

Thanks for the replies. Gave it a try and looks like this won't be an easy task, at least for someone with my limited skills. Last night I unsuccessfully attempted to remove the antenna with a soldering iron and solder sucker, maybe need 2 people, one to hold the iron on the pin and the other to pry the antenna off the tape while the solder is melted. Even worse, the entire unit got hot and was almost destroyed, it would not power up after I finished my attempt. The battery read 0v and charging did not seem to help. However, this morning it was working again, I guess the heat somehow shorted something and it went back to normal after cooling down.