I have a GPS chipset. I need to attach an intenna which has 50 ohm impedance. When i read the data sheet of the antenna it mentioned that the feed line to the antenna should have 50ohm impedance matching characteristics. So what kind of wire I should use to connect the chip scale GPS antenna to the pin on the GPS chipset which says GPS RF. Should I measure a wire of 50 ohm resisitance and connect it between the chip scale antenna and the pin on the GPS chipset or is it something else? Should I use any special coax cable which has 50 ohm impedance? What did it mean when it was written in the data sheet that the feed line should have a matching impedance of 50 ohm. Please let me know.


closed as too broad by Bimpelrekkie, brhans, PeterJ, Daniel Grillo, Asmyldof Sep 20 '16 at 17:43

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    \$\begingroup\$ If you're not familiar with the concept of transmission lines in general, and microstrip lines in particular, you're not ready to tackle a project at this level. You need to stick with preassembled modules for now. It's far too broad a topic to address here. \$\endgroup\$ – Dave Tweed Sep 20 '16 at 11:30
  • \$\begingroup\$ If you do not understand the basic concept of a "50 ohm RF connection" then why are you bothering with GPS chipsets and Antennas ? You are unqualified mister. Get studying to learn and understand these concepts. Any book on RF electronics will do (probably). \$\endgroup\$ – Bimpelrekkie Sep 20 '16 at 11:32
  • \$\begingroup\$ That means exactly "coax cable which has 50 Ohm impedance" (assuming you'll be connecting the cable directly to the pin), Technically, you should be able to measure these 50 Ohm if your meter can run at 1.5 GHz, meaning you cannot use a common multimeter. \$\endgroup\$ – Dmitry Grigoryev Sep 20 '16 at 11:43
  • \$\begingroup\$ I do not know anything about RF electronics. I just want to know how shall I make the connection (what to use, what to buy and where from) between the chip scale antenna and the GPS Chip pin.This knowledge of what to use is sufficient for my project. \$\endgroup\$ – Sriranjan Rasakatla Sep 20 '16 at 11:58
  • \$\begingroup\$ Meters that can measure at 1.5 GHz are called "Network analyzer" if you have to ask how much it costs you cannot afford it. \$\endgroup\$ – Bimpelrekkie Sep 20 '16 at 11:59

50ohm impedance refers to the geometry of a transmission line.

Coaxial cable is a popular type, with a thin central wire in a larger tube, spaced with plastic insulation. The geometry is maintained (as far as possible, and electrically if not mechanically) through coaxial connectors.

Microstrip is another type, with a track on one side of the board, opposite a ground plane on the other. For FR4 (a common PCB material), 50 ohm line has a width of roughly 2 substrate thicknesses.

At 1.5GHz (roughly GPS frequencies), the wavelength is 200mm (in air, less in plastic). Once your connection is less than a tenth of a wavelength long, so less than 10mm or so, you can often get away, without losing too much signal, with an unmatched connection, for instance a narrow track or piece of open wire. But it will be better if you make that track 2 substrate thicknesses wide!

  • \$\begingroup\$ The same applies to coaxial cable. If you keep the length you strip to a minimum you can make a reasonably good connection hand soldering the cable on to the pins of the GPS module. You will lose a little sensitivity on the GPS but it will work fine under reasonable signal conditions. Getting this sort of thing ideal is very complex and tricky, getting it so that it works well enough for a one off hack is a lot simpler. \$\endgroup\$ – Andrew Sep 20 '16 at 16:24
  • \$\begingroup\$ Upvote for being helpful :) \$\endgroup\$ – Drewster Aug 5 at 20:30

I'm sorry, but you have gotten in way over your head. Since you talk about "GPS chipset", the natural assumption is that you are trying to design and fabricate a GPS unit on a pc board. Since, by your own admission, you are ignorant of RF electronics, you are likely to do it wrong.

Worse, you are apparently trying to use a very small integrated antenna without any understanding of what is entailed. I suggest you watch https://www.youtube.com/watch?v=_VC6Yyxstd4 .

In general, you will need to precisely design your pcb traces to give the desired performance. This means that you will need to know both the layer separation AND what substrate you're using. Knowing this, you can design a microstrip transmission line of the correct impedance by specifying the proper trace width.

If the above makes no sense to you (and I suspect it doesn't) you need (as has been mentioned repeatedly by others) to start learning RF design. This is not something you can just wave your hands about, and it's easy to get wrong. It is not something you can just ask "what do I do?" on an internet site.

Good luck.

  • \$\begingroup\$ I wrote to sparkfun technical support and they asked me to use their 50ohm coaxial cable link to connect the chipscale antenna to the antenna pin on the GPS chipset. But problem is my application is space sensitive. So what will happen if I use a normal wire to connect the antenna to the pin? \$\endgroup\$ – Sriranjan Rasakatla Sep 21 '16 at 5:28
  • \$\begingroup\$ But these coaxial cables are long. So i might have to get a microstrip PCB designed. Any more info on where to get the microstrip PCB? \$\endgroup\$ – Sriranjan Rasakatla Sep 21 '16 at 5:35
  • \$\begingroup\$ @SriranjanRasakatla - You are getting in deeper and deeper. You cannont use a wire. You must use coax if the antenna and he GPS are on separate boards. If they are on the same board, you must connect them via an impedance-controlled trace. There are various ways to do this, but microstrip is the easiest and most common. And have you done any reasearch? Google? Thought not. \$\endgroup\$ – WhatRoughBeast Sep 21 '16 at 11:53

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