On the last day of CES, while still getting over some of the death curry that we foolishly ingested the night before, I had a meeting with SkyCross, who recently announced a new actively tuned multiband antenna module for smartphones. With LTE, the demand for more and more bands on a smartphone has and will continue to increase, which has at present driven OEMs to simply include more antennas, each tailored for a specific frequency. Remember that the geometry of an antenna defines its radiative properties and resonant frequency, which in turn affects gain at different frequencies. At present I’ve seen smartphones with as many as four or five antennas, which poses considerable challenge for engineering a device, as number of antennas and their placement is often in direct competition with industrial design and other considerations.

Actively tuned antennas aren’t anything new for antennas in other RF applications, but they are a relatively new thing in the smartphone and tablet space. In the past that was primarily because it was easy enough to tune a design to the handful of bands the handset was designed for. The challenge of getting an antenna with the right impedance increases when we’re talking about a wider frequency range, hence the move to either more passive antennas for more bands or an actively tuned array. To date the only smartphone I’m aware of that has an active tuning block other than what you get on the power amplifiers to match a standard 50 Ohm smartphone antenna is the iPhone 5, which has an RFMD RF1102 tuner. Of course that design only has two cellular antennas to accommodate a bunch of bands, and the active tuning there also further mitigates deathgrip, which is itself just detuning.

By antenna tuning I’m referring to the ability of some part of the RF front end to actively switch in the right amount of complex impedance and match the antenna to the transmission line in the device. In the case of most applications this means switching in some capacitors using a switch or a bunch of relays and getting as close to a VSWR (Voltage Standing Wave Ratio) of 1.0 as possible. Without going on a big long discussion about SWR and VSWR, the naive explanation is that VSWR is one of the figures of merit that defines how well an antenna can radiate, and thus having good VSWR means the antenna radiates more of the power delivered to it, rather than reflecting it back into the transmission line.

The trend in smartphone antenna design is something I’ve noted in a handful of reviews — often there’s a plastic module at the bottom of the phone with the speaker, microphone, and antenna. This is modular so the OEM can then include the right primary antenna for the right region and set of bands the phone is destined to. Look at almost any major design and you’ll see something along those lines for the primary receive and transmit antenna at the bottom.

What SkyCross is offering is the ability for OEMs to bring this plastic module to them, along with the set of bands they require, and have a single custom design tailored to their application and all the bands. They also claim to have very good (low) correlation coefficients between the two antennas on their modules, even though there isn’t much separation distance between them. Getting low correlation between the two antennas is critical for getting good gains out of MIMO (like the 2x2 MIMO in LTE) and receive diversity. The end result is a smaller solution with fewer constraints on industrial design, and possibly even better correlation coefficients for even better MIMO.

SkyCross showed off an example design and module, which had two switches visible on it along with one other package. At the bottom you can see four feed points — one for ground, two for the two antennas, and finally a voltage rail for the active components. These can then accommodate the multiple frequency bands though tuning to the appropriate configuration. I’m told that modules such as these will start popping up in smartphones in 2013.

Source: SkyCross

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  • Zink - Sunday, January 20, 2013 - link

    I like these reports on products that are one step lower level than a normal consumer tech review.
  • watersb - Monday, January 21, 2013 - link

    Me too. +1
  • name99 - Monday, January 21, 2013 - link

    I agree.

    The one thing I am curious about, as a simple number we can appreciate, is how many dB does this buy us. If I bring my OK-tuned current phone design (ie not something totally stupid, my current compromise to all the constraints of the problem) and apply this magic to it, do I improve my signal strength and so SNR by 1dB? 3dB? Something awesome like 10dB?

    And I'd second the question about power. (Though one possible way of doing this would be with MEMs, and might only involve some power when the various cavities are reshaped, ie when deliberately moving bands, and perhaps once a second or so while the radio is active, testing if the config has slightly detuned.)
  • tilandal - Monday, January 21, 2013 - link

    With antenna's you have fundamental physical limits. A small omni-directional antenna can only be so good. What you can do with something like this is reduce your need for 5 antennas to only 2 antennas but if you already have 2 good antennas you aren't going to make them any better. You actually may make them worse (for a given size). What you are buying with an active tuner is better integration at the expense of better performance. That is not to say you may not get better performance on any 2 bands as you would any 2 out of 5 bands with an array of passive antennas though.
  • rdwade55 - Monday, January 21, 2013 - link

    I really enjoyed this article, and I appreciate the author taking the time to explain one of the most important yet least talked about aspects of modern cell phone performance. I think it is fascinating how such tiny devices can pack such an array of technology, and deal with the physical reality of electromagnetic propagation over multiple bands using tiny antenna. Keep it up!
  • DuckieHo - Monday, January 21, 2013 - link

    What about increased power consumption for active tuning?
  • DanNeely - Monday, January 21, 2013 - link

    Is it to allow a phone manufacturer to create N different carrier specific models without having to create N different hardware models; or to allow creating a global phone that's compatible with all of the dozens of bands different carriers are deploying LTE to.
  • Julio2Nahvs - Monday, January 21, 2013 - link

    It is just so interesting to know that new tech things are coming. Admittedly, I don't really know anything about antennas and every language of it. However, I do understand that it is something that will enhanced the power of transmissions of signals in all these gadgets we have, particularly those that are still coming out in 2013. This Versitune Integrated Module will definitely augment the power of the coming gadgets. I would humbly entreat the excellent writer of this article, Mr. Brian Klug, to stretch this article into layman's term that the many computer-not-so literate people (including me) may understand it better relative to the particular gadget (iPhone, iPad, Android, etc.) that are highly sought-after these days. I am very grateful to you Mr. Brain Klug. MORE POWER!

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