Microwave Liquid Crystal Enabling Technology for Electronically Steerable Antennas in SATCOM and 5G Millimeter-Wave Systems  
[PERSON]  
1 Institute for Microwave Engineering and Photonics, Technische Universitat Darmstadt, 64283 Darmstadt, Germany 1  
[PERSON]  
2 ALCAN Systems GmbH, Grafenhauser Strasse 85, 64293 Darmstadt, Germany;  
[EMAIL_ADDRESS] (A.G.); [EMAIL_ADDRESS] (C.W.) Corspendence: [EMAIL_ADDRESS] Tel. : +49-15155881  
and key technologies are described in some detail in Appendix A. There are two future scenarios. Figure 1 illustrates a satellite platform scenario of a Low Earth Orbit (LEO) satellite constellation for communication links with mobiles on Earth (mobile link), where ground/user terminals might have access via flat-panel beam-steering antenna arrays, e.g., integrated into the rooftop of automotives (left). Additionally, a relay satellite in the GEostationary Orbit (GEO) is operating to establish a permanent link between a fixed ground station on Earth via a parabolic dish antenna (feeder link) and moving LEO satellites (inter-satellite link), e.g., with an electronic beam-steering horn antenna array to track an LEO satellite [1; 2]. Figure 2 (left) illustrates the 5G cellular network architecture with different cells (layers) [3; 4]: (1) macro cells (coverage layer) with high mounted sector antennas to cover large areas for the use cases in all three usage scenarios according to Appendix A, i.e., enhanced/extreme Mobile BroadBand (eMBB), massive Machine-Type Communications (mMTC), and Ultra-Reliable and Low-Latency Communications (URLLC), usually with relative low capacity, (2) micro and pico cells (coverage and capacity layer) with small antennas often below rooftops for additional capacity and coverage also for use cases in all three usage scenarios, and (3) small pico and femto cells (super data layer) with Multiple Input Multiple Output (MIMO) antennas (see Figure 2 (right)), particularly for the use cases in usage scenario eMBB with very high data rates. To enable these high data rates, the operating frequency will be shifted into the mm-wave range, whereas the first two layers are operating in the sub-6 GHz range (see spectrum recourses in Appendix A). This evolution of wireless communications is primarily driven by an ever-growing demand for higher data rates in order to meet the needs for increasing the capacity per subscriber and the  
Figure 1: Satellite platform scenario of a low Earth orbit satellite constellation to communicate with mobiles, using a relay satellite in the geostationary orbit for an inter-satellite link. Figure 2: 5G network architecture (**left**). Coverage (footprint) of Electronically Steerable Antennas (ESAs) and multi-beam antennas at certain distance \(d\), resulting in an area diameter of \(a\approx d\cdot HPBW\) for small \(HPBW\) (**right**). HPBW: half-power beamwidth. increasing number of subscribers (see Appendix A), i.e., to keep up with the remarkable speed-up of fiber optic networks. This demand on extremely high data rates and hence bandwidth leads inevitably to increasing operating frequencies of wireless communication and access systems up to the mm-wave range, where still large frequency resources are available. However, power link budget considerations in particular, which are dominated by the free-space propagation losses at these high frequencies (see Figure 3, left) require large (in terms of wavelength), highly directive, high-gain antennas to focus the narrow beam from a user terminal or mobile station toward the desired hub (satellite, access point, relay, or base station). Traditionally, this is done with a static beam formed, e.g., by a simple parabolic dish. The larger the antenna, the higher the gain, the narrower the beam for a certain frequency. This can be seen from Figure 3 (right) for an antenna example with quadratic aperture of size A = B versus frequency, e.g., a horn antenna or a microstrip patch array. The parameter is the gain G of the antenna and corresponding half-power beamwidth (HPBW).