# Comprehensive Review of RF MEMS Switches in Satellite Communications
## 4 Application in Reconfigurable Antennas
Figure 13a shows a MEMS-modulated scanning beam metamaterial antenna based on surface micromachining processes [174]. The antenna achieves an electromagnetic homogeneous waveguide with periodic metamaterial modules of unit lengths less than \(\lambda_{g}/5\). MEMS switches are integrated into each unit to modulate the phase constant \(\beta\), thus achieving scanning beams at a fixed frequency of around 8 GHz. Patch antennas are another widely used antenna type in wireless communication, particularly in base stations. However, their application in cognitive radio systems is limited due to their narrow bandwidth. [PERSON] et al. [175] provided a method using particle swarm optimization to design a reconfigurable antenna with RF MEMS switches for potential applications in cognitive radio systems. By using MEMS switches shown in Figure 13b to dynamically change the slot size, a bandwidth nearly double that of patch antennas can be achieved. The linearity of antennas is also very important for the successful operation of tunable front-ends, as signal correction is not possible after data transmission [176; 177]. Although there have been many demonstrations of frequency-tunable antennas in the past, there has been relatively less research in terms of linearity measurements and data transmission capabilities. [PERSON] et al. [178] used a switch-assisted band in a compact planar inverted F antenna (PIFA), with the antenna's center frequency tunable between 1.52 GHz and 2.25 GHz. The RF MEMS switch shown in Figure 13c is used to connect and disconnect the auxiliary band, thereby maintaining power handling capability and antenna linearity. Additionally, antenna technology for LEO (low Earth orbit) satellites is also progressing [179; 180]. Recently launched LEO satellites for Earth observation are equipped with advanced scientific instruments to gather a large amount of data. However, high-speed  
Figure 13: (**a**) The MEMS-modulated scanning antenna [174]. Reprinted/adapted with permission from [174], 2016, IEEE. (**b**) Optimized E-shaped patch antenna with RF MEMS switches [175]. Reprinted/adapted with permission from [175], 2014, IEEE. (**c**) Photograph of the antenna and its MEMS biasing network [178]. Reprinted/adapted with permission from [178], 2016, IEEE. (**d**) The novel multiple-beam antenna for satellite applications [168]. Reproduced courtesy of the Electromagnetics Academy. transmission of all collected data to Earth has become a challenge, mainly due to the relatively short time a single ground station can receive data from a transiting LEO satellite. The new multi-beam antenna shown in Figure 13d [168] can be used for a transparent high-speed data relay system. This system connects multiple LEO satellites to a single ground station through a satellite located in the geostationary orbit (GEO). The antenna switches between different sub-arrays of a larger multi-feed array using a reconfigurable switch matrix based on RF MEMS switches, to track LEO satellites. By combining digital beamforming with beam switching, the radiating characteristics of the antenna can be further improved [181; 182].