Thomas J Watson Research Center

Using an air cavity to boost the performance of a 5G antenna module

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This week the International Microwave Symposium kicks off as part of Microwave Week 2017, where I am giving a talk on new phased array packaging developments for 5G communications. I am part of the RF Circuits and Systems Group at IBM Research which has been actively working on developing new 5G millimeterWave (mmWave) phased array antenna modules operating at 28GHz and pioneering new packaging designs for transceivers and arrays that will accelerate the launch of 5G networks.

5G phased array module

IBM Research scientists Bodhisatwa Sadhu & Xiaoxiong Gu attach signal cables to the test board for phased array beam steering measurements at the IBM T. J. Watson Research Center, NY.

5G represents a new generation of wireless communications.  When networks roll out in the next few years, 5G technology is expected to support data rates higher than 1Gbps. To technically achieve this goal, a new generation of communication devices, including phased array antenna modules, have to be designed and packaged.

view of front and back of 5G mmWave phased array

Top and bottom images of the silicon-based mmWave phased array antenna module operating at 28GHz. The component is approximately 2.8in by 2.8in (approximately half the size of a typical smartphone). On the left are four monolithic silicon integrated circuits attached to the bottom of the package and on the right are dual-polarized antennas on the top of the package.

Our latest results demonstrate a module that supports a high level of transceiver and antenna integration, featuring 64 dual-polarized antennas and four RFICs, in an area smaller than the palm of your hand and thinner than four stacked credit cards. Antenna performance, which is key for 5G wireless communication, is generally measured by how much bandwidth and gain each antenna offers, and, more importantly, by how much array gain is possible by combining multiple antennas to form a directional beam that can be scanned through the air. The higher the gain, the more energy is radiated in a targeted direction. Wide bandwidth is a critical part of antenna design to support large data rates to each user. Our paper reports over 3GHz bandwidth and 3dBi gain per antenna at 28GHz, and over ± 40° scanning range for the module.


An illustration of antenna-in-package assembly breakout (top), layer stackup and board-level mounting concept (bottom).

A key innovative feature of our 28GHz antenna module is the addition of an embedded air cavity between the lid and the base of the phased array module. This feature, which works by significantly reducing the amount of energy trapped in the base substrate as compared to a cavity-less design, allows the improved antenna performance required for 5G applications.

You could liken the advantages the air cavity brings to the advantage that comes from adding an extra lens to your smart phone camera to help you take wide-angle shots or to zoom in and out.  A standard smart phone camera is a bit like having all your antennas on the normal (base) substrate of the module. Just as the external lens boosts smart phone camera performance, the air cavity feature boosts antenna performance over a cavity-less design, resulting in the higher gain and wider bandwidth needed at 28GHz.

Our previous research and work on phased arrays that operate at 60GHz and 94GHz laid the foundation for our latest packaging designs and led us to add the all-important uniform air cavity between the lid and base substrates that increases antenna bandwidth and gain. On top of the challenges of integrating and co-designing the antennas with the silicon chip is the further challenge of making all of this work in a compact, low cost form factor. With this last goal in mind, we built our latest module with a low-cost organic substrate, making the approach a more attractive choice for further commercial exploration.

I have spent the last 10 years working on how to optimize how the various system components of chips and transceivers are packaged together. It’s exciting and inspiring to be part of a team where I get to work closely with antenna and chip designers to build the next generation of communications and imaging devices.

“A Multilayer Organic Package with 64 Dual-Polarized Antennas for 28GHz 5G Communication,” International Microwave Symposium, 2017, Xiaoxiong Gu, Duixian Liu, Christian Baks, Bodhisatwa Sadhu, and Alberto Valdes-Garcia, IBM Research & Ola Tageman, Joakim Hallin, Leonard Rexberg, Ericsson



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