PCB Trace Antenna

If you’re working on a device that includes RF wireless, [Colin’s] Guide to PCB Trace Antenna Design might clear some headaches when sending off for PCBs. While it is directed at devices transmitting at 2.4GHz, the techniques and recommended equipment (read: espresso smith charts and network analyzers) should work for almost any frequency. While trace antennas aren’t as easy to implement as a measured wire, the space benefits make up for the difficulty. Unless you don’t mind how larger your project is, did someone say cantenna?

19 thoughts on “PCB Trace Antenna

  1. I don’t consider “follow the datasheet’s layout” and “acquire and use a $50,000 piece of equipment” to be Hackaday worthy.

    It would have been more interesting for the author to point out how “close enough” may indeed be “close enough” for a personal project, rather than pointing out the obvious.

  2. Cantennas (plural, not possessive) are also what most people call an antenna made from a can. It’s hard to believe, I know, but you can normally figure out which one people are talking about from the context.

    For the Spectrum analyser, you can fake it with a signal generator and a scope. You probably won’t get above 100Mhz with hobby level equipment, but it can still be invaluable.
    And I wish I could burn every smith chart in the world. So much pain.

  3. Nah, the other is a fake antenna used by ham radio operators to test their equipment. 50ohm load you can dissipate a few hundred watts in. It’s just not very common. I think I’ve seen it talked about twice, one here and one in a discussion about wifi boosting.

  4. Pringles cantennas are great for just about anything in the 2.4GHz spectrum, but they’re super directional if I’m not mistaken.

    I suppose that would work for most things if you know where your receiver will be specifically, or if you can oscillate/scan the cantenna.

  5. well i read the article, and thought it was alright. pretty much stuff you would have covered in a very basic undergrad EE course.

    …and for one glorious moment, i did think of heathkit dummy loads and then i touched myself gratuitously.

  6. @h3llphyre: You don’t need a $50,000 network analyzer for this. You could get a brand-new low end Anritsu with calibration kit for about $10,000 which can easily handle an antenna VSWR measurement. You can probably get an old used HP VNA with cal kit for a bit more. MetricTest and TestEquity (where the author got his) are where I look for refurbished equipment.

    I haven’t priced it out, but if you can pick up/make a cheap power meter or spectrum analyzer, then you can get a signal generator and directional coupler or circulator to do the same measurement, and I bet you could do it even cheaper. It would be a much more manual measurement unless you automate the sweep with your computer.

  7. One more comment: can hackaday moderate the comments, or maybe implement some slashdot-style user comment moderation? I was hoping to read some good comments in this thread but had to wade through some garbage first…

    1. @Matt,
      We delete a lot of stuff that is offensive and waaay off topic. Usually we try to leave arguments alone hoping they will fizzle out. If someone consistently insist on being a pain, we ban them. It sucks. I know I would rather people just behave like civilized adults.

  8. The word cantenna has been used on this blog dozens of times. What’s with this osgeld guy? Just constant complaining – relax, be happy. There is more to life than HackADay articles.

  9. @Matt, Caleb

    Yeah, sorry for derailing this thread further…

    I suggested slashdot-style community moderation and voting for comments in their last questionnaire/feedback request. As Had grows, it’s going to become more and more needed.

    On topic:
    The method used here makes me cringe. It’s an unusual combination of professional and hackish. However, if the money and equipment is available, I suppose it works and isn’t really a bad way to go.

    For the 2.4 GHz spectrum on a PCB you may want to look into patch antennas instead. There’s plenty of tutorials and articles available on the internet, and the approximated equations are stupid simple to work with.

    Also, although I’ve used prettymuch this exact method to tune an antenna, I have never used a network analyzer. Instead, try a spectrum analyzer. They’re equally expensive, but in my experience much more common. Make a simple wire antenna (or use a loop probe) and tape it down somewhere a reasonable distance (far field) from your transmitter. Set your scan in a narrow range around your broadcast frequency and adjust your PCB antenna for the highest signal strength.

  10. @Charper:
    I’ve used a network analyzer for tuning antennas like described in the article, but our lab actually had more network analyzers than spectrum analyzers. It is important to consider a gain maximizing method like you describe, because antennas can have their gain peak and VSWR minimum at different frequencies.

    I think the trace antennas are popular in consumer electronics because they are going to be smaller than the equivalent patch antenna and they have a more omnidirectional gain pattern. A patch antenna usually by design radiates predominantly in one hemisphere. When I’ve opened up stuff like wireless mouses and game controllers I’ve always seen trace antennas rather than patch antennas, often a J-shaped trace with a pi matching circuit at the feed point.

  11. @Charper, @Matt

    A patch antenna was too big for this application. In addition, as Matt mentioned, the directionality wasn’t what we were looking for.

    Professional + Hackish is kind of what I was going for. However, I disagree about rather having a spectrum analyzer. A network analyzer will not only tell you what your performance is but it will give details on how to improve it.

    It would be nice to use both a network analyzer and a spectrum analyzer, but I don’t think you need both. We did have access to a spectrum analyzer during FCC testing, and that was pretty interesting.

  12. @Colin

    Cool. Yeah, I didn’t necessarily mean that the spectrum analyzer was any better – just that I thought they were more common. You’re definitely right about the feedback on how to improve it. It’s easy to over-compensate with the spectrum analyzer since you have no real feedback about how close to optimal you’re at.

    However, another advantage I didn’t think of earlier to the spectrum analyzer is keeping your test equipment interference to a minimum. You can put the unit under test in it’s actual operating condition and test it at a distance with no interference.

    You’re right about the gain/VSWR optimums being different. I’ll have to look into it a bit further before I’m sure of this statement, but I believe if you’re in the ballpark on matching then your peak gain/ minimum VSWR aren’t going to be far enough off to hurt.

  13. @Colin

    P.S. Thanks for not taking offense to my previous statement: “The method used here makes me cringe. It’s an unusual combination of professional and hackish.” :) Looking back it came off a lot worse than I meant it. All in all great stuff, and thanks for sharing.

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