Antennas for low-cost Ka-band ground terminal devices

The ever-growing demand for high-speed data links together with the increasing congestion in the traditional microwave spectrum are pushing for the exploitation of higher microwave and millimeter-wave (mm-wave) frequencies, including the so-called Ka band. Major investments came along, especially in the satellite communications industry, raising the technological con-straints imposed on electronic equipment, mainly concerning performance, compactness and both reduced cost and weight. The great antenna size reduction achieved at Ka band has boosted the research towards satel-lite-on-the-move applications (SOTM), aiming the development of ground terminal antennas for both commercial and personal use. Such antennas must work simultaneously at downlink and uplink Ka bands with circular polarization and also have beam steering capabilities to keep a steady connection with the satellite. In addition, the target is also achieving a cost-effective low-profile antenna. The present thesis is focused on the design of feed antennas to be integrated in mechanical beam steering systems for the aforementioned application. Three different designs are here proposed and discussed. The first one, a wideband ridged horn antenna, was tested standalone and with a dielectric lens antenna. Once good results were achieved in both sce-narios, reducing its height would be the next goal. Thus, the second design is a cavity backed patch antenna. A comparison between both feed antennas is performed, highlighting the pros and cons of both solutions, either standalone or with the same dielectric lens antenna. Here, the first studies with a planar lens antenna are shown. Finally, the third device consists of a ridged cavity antenna with a cross-slot on its top aperture. This time, the feed was successful-ly tested with a transmitarray which allows achieving a more compact antenna system than the first one here presented. This thesis also analyzes two different manufacturing techniques, traditional milling technique and an innovative additive manufacturing (AM) technique based on metallized polymers called stereolithography (SLA). The present AM-SLA prototypes clearly illustrate the strong potential of this technology and pushes for its further assessment.

A Planar Feed for SOTM Ka-band Lens Antennas

Joana Rita Alves dos Santos Silva, Marc Esquius Morote, Maria Garcia Vigueras, Juan Ramon Mosig

Ka-band satellite technology has been drawing growing interest from public transportation industry to military applications, due to its advantages of higher speed links, smaller terminals and reduced costs. These well-recognized characteristics have also boosted the interest in exploiting the Ka-band devices for personal use in small boats or all-terrain vehicles. This paper presents a simple, low-cost and compact mobile ground terminal antenna useful for satellite communications on-the-move (SOTM) applications. The system operates in the downlink Ka band (19.7 – 20.2 GHz). It consists of a shaped dielectric lens fed by a circularly polarized (CP) patch antenna. The lens system allows a mechanical beam steering from 0° to 57° in relation to the zenith, with a scan loss below of 4.5 dB. A comparison is provided between this system and a previous one using the same lens but fed by a horn antenna, demonstrating the potential of planar structures as low profile feeders for SOTM lens antennas.

2015

Design of novel radiating elements for SATCOM phased arrays in Ku-Band

Baptiste Fernand Hornecker

The present thesis deals with the design of a planar antenna array for the communication between a civil aircraft (Dassault's Falcon) and an Inmarsat satellite. The final goal is to provide high speed Internet access in X/Ku-Band (8-12GHz / 12-18GHz), and possibly even in K/Ka- Band (18-27GHz / 17-40GHz). The study starts with the Ku-Band only, then evolves towards the transmission band and finishes with their Ka-Band counterparts. The main constraint of the thesis is that the final result should be a low profile antenna that will be easy to integrate below the fuselage of an aircraft. At the same time, the antenna has to provide a beam steering mechanism in order to track the position of the targetted satellite while the aircraft is moving. The usual way to achieve it is to implement some dedicated electronic chips below each radiating element of array. Dassault Aviation has its own alternate and more mechanical oriented solutions. Since the communication system is intended for top-notch business jets produced in small series, cost is not here a decisive criterion. This thesis assumes the existence of the beam-steering system and concentrates on a proof of concept and careful design of the antenna elements that will constitute the final array. They have to satisfy tight constraints in terms of size, return loss, mutual coupling with neighbors, efficiency, radiation pattern and dual circular polarization quality. Printed multilayer antennas have been retained as the best candidates, and themain parts of the thesis have been dedicated to their study. The thesis concludes with the presentation of an apparently completely unrelated and independant topic, namely the simulation of nanoscale 2D planar structures based on Graphene. The rationale for this last chapter is to provide a prospective study of the use of Graphene to create a variable capacitance. This component is always needed in the beamforming network of reconfigurable and scanning arrays. Our laboratory is developing a deep knowledge of the electromagnetic properties of Graphene-based devices and these varicaps could lead to very interesting applications in high frequencies, once the Graphene technology has definitely progressed. Thanks to electrostatics Green's functions, a variable capacitor based on Graphene has been simulated, and a Quantumeffect -the Quantum capacitance of Graphene- has been successfully tackled from a numerical point of view.

EPFL2016

Antennas for CubeSat Communication

Miroslav Veljovic

CubeSats are a type of small satellites (< 500 kg) that weigh several kilograms and consist of multiple Units (U) measuring 100 × 100 × 113.5 mm3. CubeSats emerged as a low-cost alternative to conventional large satellites, and have since demonstrated capabilities for communication, Earth observation, technology demonstration and many other. The primary goal of CubeSats, as it is the case with any miniaturized satellite, is to reduce the cost of orbital deployment. CubeSats are commonly launched as a secondary payload on large launch vehicles. One or several satellites are placed in a dedicated deployment system, which typically accommodates three CubeSat Units. The deployment system strictly limits the dimensions of any features on the CubeSat surface. CubeSat antennas perform the same functions as antennas on conventional satellites, such as telemetry and command, communication, navigation or inter-satellite links (ISL). However, most traditional antennas for small satellites are not suitable for CubeSats due to the profile constraints of the deployment system. Two approaches for antenna design are generally adopted. In the first, one or several low-profile antennas are placed on the CubeSat exterior. In the second, deployable antenna structures are used if the CubeSat platform does not offer sufficient dimensions. At low frequencies, the additional space is required to achieve a good radiation efficiency, whereas at high frequencies an increased antenna aperture provides a high gain. This thesis describes several antenna geometries, both low-profile and deployable, which enable several communication aspects of an Internet-of-Things (IoT) constellation of 3U CubeSats in the Low Earth Orbit (LEO). The main novelty of the proposed solutions is in their electromagnetic performance, as opposed to most CubeSat antenna designs where the mechanical design is the main achievement. The presented antennas succeed to exhibit a wide bandwidth or a specified radiation under strict size constraints. The thesis presents several wideband aperture-coupled patch antennas for TT&C and data downlink in S and X bands. A thoroughly investigated shielded-stripline feeding structure enables a wideband circular polarization (CP) with a unidirectional radiation, and demonstrates capabilities such as interference suppression of adjacent frequencies and efficient CubeSat integration. Patch-antenna arrays in L band are then presented, which radiate several independent beams for the capacity increase of an IoT machine-to-machine (M2M) communication system. The high permittivity of the antenna substrates lead to a strong coupling to the 3U CubeSat structure, emphasizing the importance of the antenna placement. Finally, different configurations of high-gain fixed-beam reflectarrays (RA) and transmitarrays (TA) are for the first time proposed for CubeSat ISL LEO communications in K band. Two novel unit cells are presented for RA and TA antennas, based on coupled loops and aperture-coupled patches, respectively. An axially corrugated CP horn antenna is designed as the feeding element for the arrays. A prototype of this antenna is fabricated using additive manufacturing in aluminum. The performance of all antennas, presented in this thesis, is validated by agreements between the calculation and 3D-simulation results and the VNA and anechoic-chamber measurements of several prototypes.