Watching the significant development of millimeter wave phased array antennas for 5G, I noted that Fujitsu Laboratories recently claimed the development of the “world's first” 28 GHz multi-beam antenna that simultaneously supports four users from a single antenna. The company also claims the antenna is the world's most compact structure, which is important for siting, particularly in urban locations and stadiums, where mounting options are restricted.
To demonstrate the concept, Fujitsu prototyped an antenna with 128 elements that generates four independent beams, each beam capable of a 2.5 Gbps data rate, 10 Gbps total through the array. The prototype measures 13 cm2 in area.
As shown in the above photo, separate arrays are used for transmit and receive. Each array comprises a rectangular grid of 16 x 8 patch antenna elements, the phase to each element controlled by what Fujitsu calls phased array MMICs mounted on the antenna panel, presumably on the backside of the patches. Each MMIC controls the phase to eight elements, split between two beams (see the wiring diagram below). For the 128 element prototype array, 16 MMICs are used to generate the four independent beams, each steerable horizontally and vertically.
Fujitsu says the MMICs can set the phase with less than 1 degree resolution — the equivalent of 9 bits — and the system design includes circuitry to detect differences in phase between the MMICs, enabling “highly accurate phase control” for any antenna array between 64 and 256 elements. Higher phase resolution minimizes side lobe interference, enabling higher data rates. Fujitsu says the design provides at least 20 dB isolation between beams, which supports data rates of 2.5 Gbps per beam (see below illustration).
In October 2017, Fujitsu issued a press release about the company’s approach to phase shifter design, followed by a presentation at the European Microwave Week (EuMW) conference in Nuremberg. Presumably, the phase shifters in the array are based on this design approach.
Additional details about the functionality and performance of the MMICs and front-end were not provided in Fujitsu’s release, so we don’t know what level of amplitude control is provided, the output power during transmit or the noise figure during receive.
Fujitsu expects to commercialize this active array antenna “around 2021,” according to the announcement. Given the company’s vertical integration and position in the Japanese market, it’s likely this technology will be deployed for millimeter wave 5G systems in Japan.