GPS: Making an active external antenna

[kripacharya]

I need to make "my own" antenna for GPS. The fewer packaged pre-built components involved the better. All discrete would be great... i think.

What goes into such a device ? LNA ? Cavity patch ? something else ?
Google shows me 1000's of such antenna, but not easy to find actual design info or internal details.

Guidance required...

 

[E Kafeman]

Step by step: http://electronicdesign.com/communications/adding-gps-chipset-your-next-design-easy
Discrete GPS LNA **broken link removed**
Probably will MAX2667 do the job better at less cost and size.

 

[kripacharya]

Hey thanks for the pointers. I had already found the Matjaz Vidmar page, but was having difficulty getting a copy of referred VHF Communications Magazines !!

Your other ref talks about a complete GPS system, but I am only interested in the external active antenna part.

 

[E Kafeman]

Vidmars LNA is all to wide and will easy be saturated by nearby cellphones, do not think it is a good idea to just copy it.
Today is it few that is designing GPS LNA with discrete components but you can take any LNA design and modify it for GPS use.
Check links above and search for GPS applications examples at Maxim and other component manufacturer and get an idea about required noise figure, IIP3, gain, bandwidth.. Wide band gain and stability relative your antenna impedance can also be important as antenna impedance at other frequencies can be very reactive.
LNA examples can be found at well known transistor producers. www.avagotech.com have rather detailed application examples for LNA's based on discrete transistors. A bit recalculation to fit your receiver system specification must you provide by your self.

 

[kripacharya]

So how much would a passive ceramic patch GPS antenna piece cost ? Say in quantities of 1000x ? No electronics, just the ceramic patch ?

 

[E Kafeman]

2€/pc + s&h

 

[chiques]

Or try this:
https://www.johansontechnology.com/datasheets/antennas/1575AT54A0010.pdf

 

[kripacharya]

So does no one have a decent design for a GPS patch antenna LNA ?!?!
C'mon guys.

 

[E Kafeman]

You need to do some thinking and searching by your self. Implementing a GPS LNA design do require some design work to fit actual needs.
For example, needed LNA gain will be depending on actual antenna gain, filter losses and required receiver input level.
If you not is prepared to do this math do I very much recommend that you buy a complete GPS unit.
I did wrote above "www.avagotech.com have rather detailed application examples".
Why not check that link? Lot of LNA designs. Both discrete and somewhat more integrated circuits.
One example with PCB board dimensions and all component values calculated in application example can be found at this page:

 

[kripacharya]

I did check the link, but got lost in their website.
I'll give it another try now and see what I can find. Discretes is what I am looking for.

 

[kripacharya]

Nope sorry. Still no luck with a discrete component design.

The Avagotech site seems to have lots of designs, but not even the url posted by E Kafeman has what I asked for.

 

[E Kafeman]

It was a direct link to a module containing two transistors, which you probably need for a GPS LNA.
Single transistor amplifier example: