## 4 Flat-Panel Beam-Steering Antennas with Low-Profile Phase Shifters with Fast Response
### Flat-Panel Beam-Steering Antenna Arrays
However, because of its low power consumption, potentially low costs for the phase shifter stack, low weight, and small form factor, it is also viable for 5G mm-wave systems, despite the \"slow\" beam-steering duration to scan the beam within \(\pm 60^{\circ}\) in about 10 ms seeming to be a limitation factor at first glance compared to much faster beamformer ICs. However, End-to-End (E2E) latency is not equivalent to the antenna beam-steering speed, as in most of the cases they are independent. Thus, in many URLLC use cases with E2E latency requirements  
Figure 36: Microwave Liquid Crystal (MLC)-based phased array layout for a basic module. Courtesy of ALCAN Systems GmbH. Figure 37: Microwave Liquid Crystal (MLC)-based receive (blue) and transmit (red) ESAs made up of a variable number of tiles, where each tile has a fixed number of radiating elements, depending on requirements. This visualization shows one possible configuration for a high-gain non-GEO antenna. Courtesy of ALCAN Systems GmbH. less than 1 ms, beam-steering is not required dynamically. Considering latency requirements of 10 ms for eMBB use cases such as broadband access in dense areas or indoor ultra-high broadband access, and assuming that users are moving by a car or walking, this beam-steering speed is sufficient to keep track and to fulfill E2E latency requirements. Even for high-speed mobile vehicles, e.g., trains and airplanes, the beam-scanning rate of about 12\({}^{\circ}\)/ms seems to be fast enough to maintain connection. Possible beam-steering scenarios and possible beam-forming architectures for mm-wave antenna arrays are given in [255]. Figure 38 above sketches the fully analog beam-steering antenna (single-beam ESA) for Point-to-Point (PtP) links as for satellite communications, where one RF chain is used for the entire array, offering the best performance in terms of cost and simplicity. Figure 38 below presents a hybrid analog/digital beam-steering antenna architecture with multi-beam capability (multi-beam ESA) for Point-to-Multipoint (PtM) links such as Massive-MIMO base stations. A multi-beam ESA is demonstrated under the public link [257]. Here, one RF chain is used per subarray, where a single RF chain comprises one PA, one LNA, and a T/R (Transmit/Receive) switch and shall be compliant with 5G power levels and TDD requirements [246; 255]. This hybrid architecture offers the best compromise between beam-forming flexibility and RF frontend cost/complexity. It requires less RF components compared to MMIC-based hybrid or fully digital beam-forming antenna solutions. Moreover, the power consumption is less. Thus, for an EIRP of about 50 dBm, the MLC technology-based \(8\times 8\) module, operating at the 28 GHz, consume less than 5.5 Watts compared to 20 Watts of an Si-based \(8\times 8\) array [247; 255]. This becomes more significant for larger arrays, since the MLC-based array does not increase linearly with increasing number of radiating elements, i.e., phase shifters. For example, in case of a \(16\times 16\) array with 4 beams and a minimum EIRP of 60 dBm, the MLC-based antenna has an overall power consumption of around 19 Watts compared to 65 Watts for antenna arrays based on silicon-based ICs [247]. Some usage scenarios are given in [255].