Why Traditional Antennas Are Here to Stay
Drexel University announced in September, 2018 that they had developed sprayed on antennas they say are just as effective as ones currently used in mobile phones and RFID tags. Spray-on antennas are similar to flexible “printed” antennas but likely prone to a number of additional problems. Let’s look at the issues with printed antennas before addressing the limits and issues with spray-on antennas, all of which mean printed circuit board antennas are not going away.
The Known Problems with Printed Antennas
I’ve worked with several printed antennas, those that are closer to a silk-screened layer or image printed by a printer than classic antenna designs. Performance has been marginal at best for most applications. If the antenna has long elements, the resistive characteristics of the paint make for a poor antenna. A short antenna such as those for WiFi or Bluetooth is less affected by this resistance. (If the antenna is 10 times longer, you’ll get 10 times the resistance.) You can use these antennas indoors to handle mobile cell phone traffic but not outdoors over long distances. This rules them out as an alternative for the massive cell phone towers we’d like to replace or at least bring down in price.
Whether or not printed antennas could be used to handle 5G is debatable. That is because these antennas are only safe to use at low power. One of the European companies made a printed antenna for the CB radios in big trucks. It ran OK at 4 watts, but if you ran more power through it, it literally melted!
The Foreseeable Problems with Spray-On Antennas
Imagine a printed design on a T-shirt, whether you made it by silk-screening or printing the design on a high-end inkjet (or equivalent) printer. After a while, all the flexing of the material leads the colored design to crack and warp. It may start to delaminate in places. The odds of this go up if it is exposed to sunlight, rain and the washing machine. If you’re using spray-on antennas in wearable devices, you’re exposing these antennas to the exact same rough conditions. However, if they bend to the point of breaking, you’ve ruined the antenna.
Bring the price down by having a very thin antenna, and you make it that much more fragile. If it is sprayed on as ink, you risk ruining the antenna if a bird scratches it or someone sprays the wall with a blast of water to clean it.
If the spray-on antenna is embedded in a laminate wall, shifting foundations, impacts to the wall and other structural issues could break the antenna, again ruining it.
Why Printed Circuit Board Antennas Remain the Industry Standard
Cheap printed circuit board antennas are established technology. MMICs are generally small PCB antennas, and they’re regularly used in cell phones. Printed circuit board antennas made by laying traces out on thin sheets of fiberglass are relatively narrow and light, but they’re incredibly rugged. Compare that to nano silver ink that could be printed on an antenna but is both expensive and brings up the concern about the toxicity of nano particles.
Conductive polymers aren’t much of an alternative, since they’re prone to thermal instability and may degrade over time. Graphene and silver ink antennas simply have poor performance; the MXene antennas performed 50 times better than graphene antennas and 300 times better than silver ink in radio signal transmission. The report didn’t state how well they performed against similarly sized conventional RF antennas.
Conversely, the fact that the technology is still in the lab means you can’t expect to use printed antennas any time soon for your project. The solution is to buy a small, rugged and affordable printed circuit board antenna that’s already on the market.