## 4 Flat-Panel Beam-Steering Antennas with Low-Profile Phase Shifters with Fast Response
### Flat-Panel Beam-Steering Antenna Arrays
The switch-off response time depends strongly on the liquid crystal mixture, which is a new third-generation LC from Merck with a bit larger ratio of rotational viscosity over the elastic constant \(\frac{\gamma_{rot}}{K_{11}}\) than GT7, which was specifically synthesized for this application: with current design choices, it is in the range of 30 ms for an \(h_{LC}\) of about 4 um at room temperature. It should be noted that the switch-on response times are an order of magnitude faster and the overall performance is governed by the distribution of the phase change rate rather than a minimum or maximum value [179]. Therefore, it was not surprising that the empirical result for the beam-steering duration of phased arrays based on these phase shifter stacks was about 10 ms to scan the beam from \(-60^{\circ}\) to \(+60^{\circ}\) (beam-scanning rate of 12\({}^{\circ}\)/ms); i.e., it was less than the switch-off response time of 30 ms (maximum), which consolidates our experience. Again, use is made of the modular concept with several basic modules of \(8\times 8\) radiating elements with an appropriate size to meet the application's specific requirements. Each module is built up in different stacks, which mainly consist of a feeding network stack, a LC-phase shifter stack, and a radiator stack, where all parts are designed independently and in a modular fashion. Figure 36 shows the schematic of an antenna module. At the end of the assembly, a radom will cover the antenna on top and a Low-Noise Amplifier (LNA)/Power Amplifier (PA) with an Rx/Tx-modem as well as the control unit is placed behind the feeding network. Herein, the core LC-phase shifter stack consists of two glass sheets with the metallic structures and the alignment layers separated by spacers where the LC material is filled in between. It is fabricated with standard LCD processes by an LCD manufacturing  
Figure 35: (**a**) Ku-band TV reception demonstrator with ALCAN’s first-generation antenna to steer the beam between different GEO satellites, using a 100 μm LCD process for the phase shifter stack. (**b**) Horizontal and (**c**) vertical antenna pattern for a beam in the boresight direction (note the different angular scales) [253]. Courtesy of ALCAN Systems GmbH. company. This allows large-scale fabrication as well as virtually any aperture size, including segments or antenna groups, thus providing a cost advantage [179; 246]. This technology is entirely passive, and biasing requires only low power and takes advantage of existing LCD driver technology. Controlling up to 512 radiating elements will consume a power of less than 1/2 Watt, which represents a 30 times improvement over a standard semiconductor-based phase shifter [256]. Moreover, by leveraging the existing mass production capabilities of LCD production lines, as well as the low marginal cost of producing additional types of LC panels, ALCAN claims to be able to reduce the LC phase shifter costs by 100 times to around 300 $/m\({}^{2}\) compared to semiconductor-based phase shifter costs, which are estimated to be around 30.000 $/m\({}^{2}\) when using 30 cm diameter wafers [255; 256]. At present, an antenna prototype is aimed for satellite ground terminals, which are this time made up by stacking unit tiles, where each identical tile has a fixed number of radiating elements (typically 256, 512, or 1024). The Rx (blue) and Tx (red) aperture for non-GEO ground stations in Figure 37 will be operating in the Ka-band. The antenna will be mounted onto a roof and will provide more than 150 Mpbs throughput, while the power consumption without Low-Noise Block or Block UpConverter (LNB or BUC), and modem is below 30 W.  
At first, ALCAN's second-generation antenna was aimed for ground and user terminals of MEO/LEO satellite constellations only [179].