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I saw many designs for creating DIY antennas for NOAA (~137MHz) and ADS-B (~1090MHz) but never seen it in a PCB implementation.

So I have a rookie question: why nobody uses PCB antennas for such tasks?

I believe it is easy to make even with the "Iron Transfer Method" and get a smaller size with the same conductor length (making the conductor "wavy"). What might be the catch?

P.S. I know nothing about antennas :)

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A simple antenna has at least one dimension that is approximately, or larger than,

$$L = \frac{1}{4} \lambda = \frac{1}{4} \frac{c}{f}$$

where $\lambda$ is the wavelength, which can be computed from the speed of light $c$ and the frequency $f$. For 137 MHz, that's 55 cm or 1.8 ft. That's a pretty big PCB! At 1090 MHz, this is less of a problem, though.

The next question is what design you're using. The simplest antenna design is a rigid wire one quarter wavelength long (the length I mentioned above), but if that is what you want, a piece of solid-core wire is cheaper and easier to obtain than a PCB.

Some more complex antennas that can be readily made on PCBs are specifically wide-bandwidth, for receiving over an unusually wide frequency range, or more directional, for long-range point to point communication — both not being the problem these applications are trying to solve.

And the squiggly complicated PCB antennas you may have seen are trying to solve the problem of stuffing a decent antenna, with needed electrical properties, into a tiny space, as in a cell phone. (Or just avoiding needing a separate component to solder on.) The tradeoff is that these ‘electrically small’ antennas may have different matching requirements, narrower bandwidth, and be less efficient, which matters mostly for transmission.

So, overall, yes, you could make a PCB antenna for these signals, but it's not the right technology.

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  • $\begingroup$ Antenna efficiency isn't so important for reception, as an inefficient antenna attenuates signal and noise. $\endgroup$ – Phil Frost - W8II Aug 28 '18 at 18:28
  • $\begingroup$ @PhilFrost-W8II Fixed. Thanks. Gah, I'm making too many mistakes of basic theory lately. $\endgroup$ – Kevin Reid AG6YO Aug 28 '18 at 19:14
  • $\begingroup$ @PhilFrost-W8II That's true for HF and below. However, for VHF and above when signals are not very far above the noise level, not so much. $\endgroup$ – Mike Waters Aug 29 '18 at 1:29
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    $\begingroup$ @PhilFrost-W8II Man made noise is starting to creep into the VHF range. But efficiency can be important particularly at these frequencies where atmospheric noise is minimal. I just completed an IoT design (700 MHz) where an improvement in receive antenna efficiency made the difference in marginal to functional operation. $\endgroup$ – Glenn W9IQ Aug 29 '18 at 1:32
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    $\begingroup$ Interesting. I stand corrected. $\endgroup$ – Phil Frost - W8II Aug 29 '18 at 1:35
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PCB is an appropriate and useful way of making antennas for higher frequencies, say from 900 MHz and up.

My company made thousands of GSM antennas for window mounting (in the days of car-installed cell phones). These were a fan dipole for 900 and 1800 MHz.

Here is a PCB antenna I found on the web, for example: enter image description here

We also made all sorts of high gain Omni antennas, for 1.3 GHz video links, 2.4 GHz, 5.8 GHz, on long thin PCBs housed inside thin wall fibreglass tubes. No zigzags, these were full sized stacks of dipoles fed with transmission lines, all on the board.

I would say the best way of mass-producing a modest gain 1090 MHz Omni, say 6 to 9 dBi, is with a PCB antenna. It can be done with soldered coax alternating inside and outside, or with little brass tubes soldered to coax cut just so, but the PCB is the simplest and most repeatable. It need only be 10 mm wide, so doesn't cost very much. Of course it takes some simulations and then several prototypes to get the design right, so not the best route for a one-off.

Here is an example of an ADS-B antenna made with PCB, and a picture taken from this page.

enter image description here

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I'm guessing by PCB antenna you mean specifically the kind where the trace folds back on itself, resulting in a physically smaller antenna?

There are non-PCB antennas which use similar techniques to achieve a smaller size. For example, hams will be familiar with the ubiquitous rubber ducky antenna on VHF handhelds. Here, G4ILO builds one for the 2 meter band, which at around 145 MHz is pretty close to your 137 MHz target.

enter image description here

Rather than printing a trace on a PCB, a wire is coiled around a form. The coil adds inductance which makes the antenna appear longer electrically than it is physically.

Printing a meandering trace on a PCB has the same effect. As you can see in the image above, this antenna is about 6.5 inches (without any shortening, it would have been 19.5 inches at 145 MHz) which is a pretty large PCB. The choice to manufacture an antenna on a PCB versus wire is usually for cost reasons, but at this size the economics might not work out.

1090 MHz however is not far in frequency from GPS, where PCB antennas are very common. I'm sure somebody is using PCB antennas at this frequency.

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  • $\begingroup$ Very interesting, thank you. $\endgroup$ – Deliaz Aug 29 '18 at 7:47

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