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Radically Rethinking Antennas

Antennas are a critical part of the RF signal chain, that’s not news. As the last stage on the transmit side, and the first stage on the receive side, a system’s performance depends to a large degree on an antenna’s ability to get the PA’s signal out, or to capture that minuscule ambient RF energy. The rest of the signal chain, low noise amplifiers, synthesizers, filters, and even DSP-based algorithms can only do so much if the antenna’s SNR is inadequate.

In the early days of wireless, antennas were constructed of wires, pipes, or tubes, and sized to both the wavelength and the power levels (for the transmit side). These are the classic antennas which most people think of (and movies loved to show) when the word “antenna” is used. There are many configurations available, such as long wire, monopole, dipole, folded dipole, Yagi-Uda, and dish, in both single-ended (unbalanced and grounded) and balanced (ungrounded); it’s a long list of creative solutions.

Dish Antenna
Image courtesy of NASA

Dish Antenna

Image courtesy of NASA

Yagi Antenna
Image courtesy of Antennaskit.com

Yagi Antenna

Image courtesy of Antennaskit.com

Antennas come in so many sizes, shapes, configurations, and implementations that even a large photo gallery would be inadequate, but the dish and the Yagi-Uda are two easily recognized versions which the public associates with them– even though they don’t know their names. (Image source: NASA; Protel Antennas)

Still, you can distill that list into just a few basic approaches, with many of others being ingenious variations on the few basic antenna configurations. Let’s call this phase Antenna 1.0 , where the antenna is somewhat visible, and the circuit/system it supports is physically separated with little direct electromagnetic interaction (except for the obvious need to connect to each other and match impedances, of course). You can substitute antennas as desired without modifying the transmitter or receiver, as long as you keep that Voltage Standing Wave Ratio (VSWR) down.

Then came what I’ll call Antenna 2.0 . This approach uses the PC board cladding as the antenna elements, etching the antenna design into the PC board itself using standard microstrip and stripline techniques. Yet while the fabrication technique is the same as what is used for the rest of the board, including (exposure, etching, drilling, plating) – and that’s one of the virtues of this approach – their topology is not necessarily conventional. Instead, clever designers take advantage of the availability of the PC copper to create multiband antennas, often with added filtering, rolloffs, and other desired characteristics. Of course, the placement of components on the board affects the antenna performance, so the antenna and the board design are tightly linked designs.

Next comes Antenna 3.0 , with chip antennas made of ceramic-based multilayer fabrications. These have the virtues of small size and low cost, as well as being SMT components compatible with standard PC-board loading and soldering. Chip antennas have become the antenna of choice for narrowband applications above 1 GHz, and are the only choice for many of today’s handheld devices. It’s even possible to make the chip antenna part of the RF IC itself, as part of a system-on-chip (SoC).

Though I haven’t had time to research credible information about their history (sorry), there’s a good explanation of how they work here, with many more also available. Since the PC board is the ground plane for the chip antenna in most cases, the antenna placement and board design/component placement are linked to a large extent.

Now we’re seeing Antenna 4.0 , which uses metamaterials to create configurations which are simply not possible using previous techniques. Metamaterials are “artificially engineered” materials (an awkward concept) which can exhibit negative refractivity, and so cause an electromagnetic wave to reflect in a direction different than it would using conventional “natural” materials. This opens up a very new path to antenna design all the way from concept through implementation.

But why stop at phase 4.0? Another fascinating antenna-forming technique is additive manufacturing (AM), often called 3D printing, and which I’ll call Antenna 5.0 . Using this layer-by-layer approach to fabrication of both the conductors and insulators, it is possible and economical to literally build antenna structures which were simply not possible using metal bending, etching, attaching, and even sputtering. As a result, antennas which were previously only imaginary (or had not yet been envisioned) have become very possible.

But in the antenna world — which in its earlier years was relatively slow moving, with the major change being reduction in size as wavelengths decreased – there’s yet another change: the antenna-less antenna, what I designate as Antenna 6.0 . “Antenna-less antenna” may be a play on words, or a matter of semantics, but companies such as Fractus Antennas are promoting what they call “antenna boosters” which mount on the PC board, like the chip antenna. However, these virtual antennas (based on mathematical fractals) replace the chip antenna and its limited bandwidth, and interact with the PC board to create multiband antennas, which are increasingly needed with today’s smartphones, and will be even more so with 5G deployment; there’s a good explanation of the principle here.

A lot of the “credit” for ability to conceive and deploy these newer antenna is made possible by sophisticated EM-field modeling tools, which allow the configuration to be analyzed in detail. This is a capability which was not available for the earliest antenna designs, which were often developed using a little analysis, a lot of instinct, and even more trial-and-error. Modeling tools have changed antenna design from largely being “magic” and experience to a much-more rigorous discipline.

Obviously, advances in antenna technology will not obsolete their predecessor implementations. There’s still a need for antennas from each phase, depending on the application priorities, constraints, and real-world demands. Still, it’s nice to have such a wide menu to choose from, and no longer be limited to the highly visible “classic” designs, regardless of how many memories or visuals are associated with them.

What’s your antenna exposure? Have you had any experience with using metamaterials, additive, or antenna-less antennas?

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1 comment on “Radically Rethinking Antennas

  1. ThomasMaloney
    July 17, 2018

    I think that most people would just stick to the knowledge of whatever they have seen in media rather than going to analyse what kinds of antennas there are. Very few people would actually need to learn about the different types and how it affect their communications channels to be honest. It's a good thing that we have well trained professionals and experts who are able to advise us when we need that information though! Haha!

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