Antennas
We have focused on the conception of novel low-cost planar antenna systems that enable pervasive and straightforward integration of active electronic and opto-electronic components on the antenna platform, that feature best-in-class performance in terms of bandwidth, radiation efficiency, and compact footprint, that maintain their excellent performance when deployed in harsh indoor environments, and that are compatible with mass production processes. First we applied conventional high-frequency laminates extending this to unconventional materials, which typically do not serve as antenna building blocks, but that are cheap and readily available in the envisaged applications.It was found that the air-filled Substrate-integrated-waveguide technology is the perfect candidate to address the very strict ATTO requirements.
Radio-over-fiber interconnects
To deliver very high-bandwidth and high-frequency signals to a huge number of antennas, it is important to realize a low-power and low-cost interconnection technology. We have investigated different ways to transport radio signals over fiber. In the end, it was concluded that the most efficient solution is to directly modulate radio signals on an optical carrier. This allows to realize very compact ATTO-cells that consume little power. Dedicated optical receivers (resonant transimpedance amplifiers) that were tuned to the radio signal frequency were designed to ensure low power but high- quality transfer between the optical signal and the antenna. Similarly, also transmitter circuits have been realized. At 28 GHz an intensity modulated approach was adapted. At 60 GHz, single side band transmission was realized using a combination of electrical and optical Q-hybrids. We have demonstrated these receivers chipsets around 28 GHz and evaluatied the same approach at 60 GHz.
Exposure
The ATTO approach is disruptive in the sense that a huge number of antennas will be deployed within a given area. One might assume that the level of the electromagnetic radiation would increase significantly. However, this is not the case. Because, the communication only happens over a very short reach, the transmit power can be drastically reduced. We were able to conclude that in a typical ATTO scenario the exposure levels will be comparable with what is expected in a Massive MIMO 5G scenario (e.g. at 10m, for 5W, industrial environment). Moreover, mm-wave 6G distributed massive multiple-input multiple-output (DMaMIMO) base stations at 28 GHz were investigated and with equal power, distributed base stations contribute 2 to 3 times less to exposure than collocated base stations.
