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At IMS, Focus on the Millimeter-Wave Technology

At IMS, Focus on the Millimeter-Wave Technology

by Barry Manz, President, Manz Communications, Inc.

Boston has proven to be one the best cities for hosting the International Microwave Symposium, so it seems fitting that it will be there again next month as 5G transitions from “coming,” to “here.” This will be my 37th (gulp) MTT/IMS, which covers everything from the emergence of GaAs and the MMIC, to the first through fourth generations of cellular, multiple peaks and troughs of defense spending, the rise of GaN, and advances in virtually every technology and component used in RF, microwave, and millimeter-wave systems and instruments. Even with all the accumulated breakthroughs over the years, the technology displayed and papers presented at IMS in Boston should be show-stoppers. 

The fifth generation of what used to be called “cellular radio” is matched only by the first generation in significance. Yes, 2G, 3G, and especially 4G, delivered significant improvements to the user experience, but 5G is a truly massive endeavor. It’s like what would happen if say, a dozen very knowledgeable people within the entire RF and cellular ecosystem put together a no-holds-barred list of what they think the next generation should accomplish, and then decided to do it. So, while vendors last year were promoting their preliminary solutions, this year they will be demonstrating hardware (and software) solutions when infrastructure is being deployed and end-user devices with some 5G functionality will be offered later this year.

And there should be a lot to see, from the component level through complete subsystems. One of the most interesting aspects of 5G, for me at least, is how millimeter-wave technology will be deployed in small cells and (especially) end-user devices. 5G marks the first use of phased-array antennas in wireless applications as the industry moves toward millimeter wavelengths. These antennas, formerly the domain of defense systems, will be essential to enable communications at the highest frequencies, owing to the unique propagation characteristics in this region, such as short range, line of sight only, and severe attenuation.

It’s interesting that, although it’s certainly possible that some defense systems use millimeter-wave phased-arrays in an AESA architecture, the first use of these antennas en masse will be in commercial wireless systems. Some of the goals in designing these arrays include extending transmit range while simultaneously reducing form factor, the ability to support simultaneous independent beams, and high-resolution beam steering over a broad scan range. Multiple organizations have been developing phased arrays, focusing at 28 GHz, where Verizon has developed a fixed wireless access (FWA) solution and is deploying it in cities throughout the U.S.

For example, a design from the University of California San Diego demonstrated an array at 29 GHz using 32 elements, each delivering RF output of 13 dBm, which was fabricated in silicon germanium (SiGe). Each 32-element package delivers saturated power of 32 dBm EIRP. Another project, conducted by IBM Research at 28 GHz, uses a SiGe chip containing 32 elements with 128 elements in the package. Each chip delivers saturated power of 16 dBm while the entire package produces 54 dBm. Total die area is 166 mm².

Other reported efforts include a 32 x 32-element array with 1024 elements in the package developed by Huazhong University of Science and Technology, a 64-element array from Nokia Bell Labs that uses 16 MMICs and produces 48 dBm EIRP, and efforts from LG, and others. The prevailing device technologies appear to be SiGe, BiCMOS, and CMOS.

Integrating millimeter-wave capability and phased-array antennas in small cell base stations is difficult enough, but in a smartphone it’s a vastly greater challenge, not just because there is little internal real estate available but that signals at millimeter-wave frequencies are attenuated by almost anything placed in their path—like your hand. And unlike fixed terminals whose operating environment is reasonably static, smartphones are operated in an unlimited number of positions.

Other seemingly insurmountable obstacles include very close proximity of metallic objects within the phone, polarization mismatch, antenna surface currents changing impedance, and components such as speakers, microphones, and sensors relegating the antenna to the edge of the device.

Qualcomm’s QTM052 module has shrunk by 25% since it was first shown in early 2018.

All these issues will collectively reduce the performance of the millimeter-wave subsystem in the phone, so reliable communication requires use of every advanced technology that can minimize the losses sustained by the factors noted above (and others). Beamforming, steering and tracking, along with massive MIMO and MU-MIMO integrated within base stations, can substantially improve link performance, but the outcome in practice remains to be seen.

Qualcomm has taken upon itself the challenge of proving that millimeter-wave capabilities within mobile devices can be achieved and has invested substantial resources to prove it. The company has demonstrated that it can maintain a connection even when bouncing signals off buildings and has produced the most highly-integrated millimeter-wave transceiver by far, the QTM052, which offers 800 MHz of bandwidth at frequencies including 26.5 to 29.5 GHz, 27.5 to 28.35, and between 37 and 40 GHz.

The device contains a 5G NR transceiver, power management IC, silicon RF front-end, and an entire 24-element phased array antenna that performs beamforming, beam steering, and beam tracking. When combined with the company’s Snapdragon X50 modem, the QTM052 is essentially a complete radio and antenna in a device measuring 18 mm long x 5 mm wide. To overcome blockage, the QTM052 and X50 can switch to other beams produced and received by up to four modules mounted in the four corners of the phone. The latest version of the QTM052 is 25% smaller than the first and should be easily accommodated in tablets, TVs, streaming devices and (presumably) Verizon’s 5G Home customer premise equipment. Based on the company’s success so far, the device may get smaller yet.