## 1 Introduction  
The interest in satellite communications has grown exponentially in recent years. With the massive deployment of non-geostationary orbit (NGSO) LEO/MEO satellite constellations, a great variety of high-speed and low-latency communication applications are showing up [1, 2, 3, 4]. The upcoming scenario is driving the development of new antenna front-ends capable of tracking one or more satellites while providing a high data rate and low-latency two-way communications. Traditionally, tracking GEO satellites has been a relatively easy task, since a parabolic antenna pointed towards the satellite position can provide good communication with the satellite transceiver, and mechanical steering could provide uninterrupted communication with the satellite. However, the antenna front-end configuration is not that simple for NGSO networks, where satellites are moving with respect to the land-terminal. Although tracking the satellite as it moves may seem easily solved with a mechanical structure that follows its movement, which is the basic principle of Satcom-on-the-move (SOTM), the satellite eventually crosses the horizon and the antenna must perform a handover to track a new satellite in the line of sight. Mechanical systems show very poor behavior at switching between satellites, with very slow responses that imply periodic losses of the communication link, thus greatly reducing their reliability. In this context, active antenna arrays with electronical steering are a great alternative to mechanical positioners. These terminals can achieve response times of the order of one millisecond to continuously track the satellite or to perform a satellite handover with a much faster response without the need for mechanical actuators. Another major advantage of these active antenna terminals is that they do not require a parabolic structure to achieve the needed directivity. Therefore, the use of these systems allows for the design of ultra-low-profile devices, which has driven the uprise of a great amount of new SOTM applications, such as unmanned aerial vehicle, connected cars, commercial flights, and other scenarios where satellite communications is the only choice. In particular, in recent years, great efforts have been made on the development of new Ka-band SOTM terminals for land mobile, maritime or aeronautical platforms that require low-profile antenna front-ends capable of providing high data rate and low latency of the order of 10 milliseconds from emerging LEO/MEO satellite networks, compared to the 300 or more milliseconds latency with GEO satellites. In this context, phased array antennas, also known as active electronically scanned arrays (AESAs), play an important role owing to their characteristics of low profile, size and weight, and high reliability because there are no moving parts to fail. AESAs can also steer beams in microseconds and support multiple, simultaneous, and independent beams [5; 6]. One key difficulty in the design of Ka-band Satcom front-ends is the compact and cost-effective integration in a single PCB of the antenna elements with the high number of active and passive radio frequency (RF) components such as low noise amplifiers (LNAs), power amplifiers (PAs), phase shifting devices, hybrid couplers, etc., that require not only good thermal handling but also considerable mounting space and adequate power consumption. The maturity reached by microwave monolithic integrated circuits (MMICs) and the latest advances in silicon technologies such as SiGe or CMOS have helped to address this challenge for a large-scale deployment [7; 8]. Nowadays, a way to solve the integration problem is placing the antennas on-chip, as in [9], where a W-band 4 \(\times\) 4 wafer-scale phased array has been developed and reported. However, it is important to note that this approach requires identical sizes for the chip and the antenna aperture to be efficient, making it very useful at frequencies above 60 GHz, and to drastically reduce the price of phased arrays.