## 3 Passive Phased Arrays with Integrated Metallic and Dielectric Waveguide Phase Shifters
### Electronic Steerable Horn Antenna Array  
For a relay satellite in geostationary orbit, establishing a link between moving low-Earth orbit satellites and a fixed ground station on Earth according to Figure 1, a light-weight Tx/Rx electronic beam-steering horn antenna array was aimed to design for down- and uplink in the frequency bands of 23 to 23.5 GHz and 27 to 27.5 GHz, respectively, within the project Lightweight InterSatellite Antenna-Electronical Steering (LISA-ES) funded by the German Aerospace Center (DLR) [75; 76; 176]. The desired scanning range is \(\pm 11^{\circ}\), aiming for a phase change rate of at least \(5^{\circ}\)/s to track the LEO satellite. For the final application, a \(16\times 16\) horn antenna array according to Figure 14, i.e., with 256 phase shifters for one polarization, is aimed to implement into the satellite. To achieve beam-steering capabilities, partially the LC-filled waveguide phase shifters sketched in Figure 14 aimed to plug into each branch of the rectangular waveguide feeding network for robustness, reliability, and long lifetime, to each horn of the array. All components are built up of micro-machined low loss, which was hard plastic (Rexolite 1422) electroplated with Ag/Cu for minimum weight. The materials used are space approved, including the LC [75; 76; 176]. The first experiments in the lab have been carried out with waveguide phase shifters in a split-block design made of brass [68; 69]. To assure single-mode propagation in the LC-filled waveguide, smaller dimensions of \(a=5.5\) mm and \(b=2.2\) mm are used than those for regular waveguides in this frequency range. The design and measurement results with LC GT5-26001 over a frequency range from 21 to 35 GHz are given in [68; 69]. Over the frequency range from 23 to 27.5 GHz, the matching is better than \(-12\) dB. Only below 23 GHz does it go up to more than \(-10\) dB. The _IL_ is between \(-2\) and \(-4.0\) dB in this range, which was underestimated in the simulation, because waveguide losses could not be estimated precisely and the effects of the electrode sheets could not be taken into account in the simulations. The differential phase shift \(\Delta\varphi\) is above \(450^{\circ}\) for electrical biasing; hence, the FoM was about \(120^{\circ}\)/dB in the desired frequency range and \(130^{\circ}\)/dB in the frequency range of 27 to 32 GHz. The response times of this phase shifter were estimated to be between one and two minutes at room temperature. Since the phase shifter is designed for a temperature-controlled antenna at \(60~{}^{\circ}\)C, improvements in the order of magnitude of 10 to 12 is expected for the response time. Based on these promising results, a light-weight \(4\times 4\) horn antenna array prototype with plug-in LC-based phase shifters is realized for individual measurements [75; 76]. Each waveguide phase shifter with a length of 12 cm consists of an LC-filled Rexolite container, including the biasing electrodes, which is enclosed by a galvanically deposited silver-primed copper cladding of 0.5 mm thickness, and additional aluminum flanges with screws with a total weight of 12 g only. For biasing the LC-phase shifter, custom-built electronics provide up to 513 voltage channels. One provides a fixed voltage pair of \(\pm 164\) V, while the other channels are tunable between \(\pm 164\) V. In this way, each phase shifter can be individually tuned to a desired differential phase shift. The final outcome of various design iterations for environmental and RF-performance tests in [76] are as follows. In the frequency range from 23 to 27.5 GHz, reflection is below \(-13.7\) to \(-18.7\) dB in the lower band and below \(-11.1\) to \(-11.7\) dB in the upper band. The measured maximum differential phase shift is about \(450^{\circ}\) as predicted by simulations. However, the measured insertion loss varies between \(-4\) and \(-6\) dB in the frequency range above, and it is larger than expected from simulations.