# Phased Array Antenna Analysis Workflow Applied to Gateways for LEO Satellite Communications
## 1 Introduction  
Low Earth Orbit (LEO) is presented as a complement to 5G communications, improving the bandwidth of mobile communications, giving global coverage, and allowing a wide range of Internet of Things (IoT) applications or high trust communications. 5G plays a key role in the development of high-density sensor networks. The 5G system increase data rates by 10 times that of the traditional Long-Term Evolution networks, to an average of 10 Gbps with a 1 ms round-trip latency. This high bandwidth can accommodate many connected devices per unit area under the IoT framework [1]. High data rate services are not available in rural places or onboard ships and aircrafts since terrestrial networks do not cover the whole world. SATCOM and SATCOM-on-the move (SOTM) are essential to achieve communications with global coverage. The idea of delivering internet connectivity from space has made a significant resurgence. Although some proposals for LEO mega-constellations of satellites emerged in the 90s, it is not until now that these projects are being implemented. Technical innovations of the past decades, such as increased performance resulting from the use of digital communication payloads, advanced modulation schemes, multi-beam antennas, and sophisticated frequency reuse schemes, as well as overall cost reductions from advanced manufacturing processes and reduced launch costs, have enabled the launch of mega-constellations of low-cost satellites [2]. Mega-constellations refer to a constellation composed of hundreds or thousands of satellites orbiting the Earth [3]. In particular, LEO refers to orbits between 500 and 1000 km, having reduced path loss and delay compared to Geostationary Earth Orbit (GEO), which is located 35,786 km above Earth's equator [4]. LEO is presented as a complement to5G communications, improving the bandwidth of mobile communications, giving global coverage and allowing a wide range of Internet of Things (IoT) applications or high trust communications. This system could also give internet service to remote areas [5]. Figure 1 illustrates a typical satellite communication system. The space segment consists of the satellites, and the ground segment will be composed of three different types of elements: the Tracking, Telemetry and Commands (TT&C) stations, the gateways, and the user terminals. The TT&C stations are responsible for monitoring the satellite in orbit and will be scarce in number and distributed across the world. The gateways are used to give users' terminals access to the Internet through the satellites. Contrary to what happens with conventional satellite systems, in this type of system a large number of gateway antennas distributed across the world near or co-located with Internet peering points are required. The development of large LEO and Medium Earth Orbit (MEO) constellations, planned by companies such as SpaceX, Telesat, OneWeb and Amazon will require ground terminals able to track multiple satellites working at Ku-Ka-bands. Parabolic dish antennas have been the defacto choice for SATCOM Earth antennas. They provide benefits such as high performance, low power consumption, and low cost. However, they have limitations, such as weight, size, lower efficiency [6] and its mechanically pointing. To communicate with LEO satellites, where orbital movement is faster than GEO, the pointing needs to change quickly. This is where phased array antennas have emerged as a solution. Relative phases of signal feeding of the patch antenna are varied to alter the radiation pattern so that the phased array points in a specific direction electronically without the physical movement of the antenna. Moreover, dish antennas become inefficient and costly when tens or hundreds of beams are required, as is the case of current LEO constellations where many tens of beams per satellite for Mobile Satellite Services (MSS) and hundreds of beams per satellite for wideband data systems are required [7].