Radio Technologies for Broadband Connectivity in a Rapidly Evolving Space Ecosystem

1.      L. Dufour, F. Guinot, G. Goussetis, L. Datashvili, “Origami deployable reflector for small satellites”, 3rd International Conference on Advanced Lightweight Structures and Reflector Antennas, Tbilisi, Georgia, 19-21 September 2018 – BEST PAPER AWARD BY EURAAP

 Abstract: There has been a growing interest in the recent years in high gain reflector antennas for small satellites. This paper presents a deployable antenna reflector concept for small satellites which introduces new ways to fold an antenna reflector (a doubly curved surface), taking inspiration from the field of origami. A methodology to design faceted origami patterns approximating any reflector shape is presented, as well as discussions on the impact of the curvature on the folding.

2.      L. Datashvili, N. Maghaldadze, M. Friemel, L. Dufour, L. da Rocha-Schmidt, D. Andrade, T. Luo, ”Densely Stowable and In-Orbit Deployable Space Antennas for Very Small Satellites.”, Proceedings of the 3rd International Conference ”Advanced Lightweight Structures and Reflector Antennas”, Tbilisi, Georgia, 19–21 September 2018

 Abstract: Key criteria for Earth observation (EO) from space are the proper wave lengths (e.g. IR, visual optics, radar, etc.) as well as the spatial and temporal resolution. There is an increasing trend to cover such criteria with (clusters of) properly positioned small satellites in lower earth orbit, with the latter being also beneficial for achieving good resolution. The resolution and data volume and thus also the quality and surface precision of the used reflectors are not only essential for the quality of the EO data, but also for the data downlink when transmitting relatively high amounts of data while being in contact with related ground stations. The main focus of this paper is given to different small densely stowable and after deployment precise reflector designs, which can be derived from the FlexRS® technology of LSS. These are for example radially deploying and also umbrella type reflectors, where both types are mainly based on shell membranes made from carbon-fiber reinforced silicone (CFRS) and in other cases also from knitted metal mesh like gold-plated Molybdenum. Laboratory models for shell-membrane designs have been also established and many deployment tests and also shape accuracy measurements have been carried out.

3.      F. Vidal, H. Legay, G. Goussetis, M. Garcia Vigueras, S. Tubau, J.-D. Gayrard, “Development of a Modular Simulation Tool for Flexible Payloads Design and Benchmark with an Application to LEO Satellite Payload Architectures for a Ka-band Broadband Mission,” 4th ESA Workshop on Advanced Flexible Telecom Payloads, ESTEC, 4-8 March 2019

Abstract: This paper presents a tool that is being developed to assist the design of flexible payloads and to benchmark various payloads and antenna architectures on their ability to match changing non-uniform user traffic. The methodology is the following: first the selected payloads that include a variety of antenna subsystems are sized to produce the same throughput for a uniform distribution of users, then they are statistically characterised for a wide range of traffic scenarii with uniform to sparse user distributions. An indicator is proposed to characterize the non-uniformity of user distributions, the variation of the capacity versus this user distribution indicator is then derived. A resource allocation tool was specifically developed for this assessment. This tool will be mostly beneficial for the high level trade-offs, and will compare the payload and antennas solutions on their flexibility characteristics as well as on their complexity. As a first use-case, a megaconstellation scenario in LEO with multiple beam coverage in Ka-band is considered. 2 passive payloads with fixed frequency allocations to beams and one including beam-hopping are described and benchmarked. The statistic representation of the throughput with respect to the asymmetric distribution indicator clearly highlights the benefits of beam hopping.

4.      S. Mercader Pellicer, F. Rigobello, G. Goussetis, L. Dufour, D. Bresciani, H. Legay N. Fonseca, “Dual Ka-Band Multiple Beam Reflector Antenna for Western European Coverage,” 13th European Conference on Antennas and Propagation, Krakow, 31 March-5 April, 2019

Abstract: This paper presents a dual-band multiple beam reflector antenna for a Western European coverage. The dual configuration comprises a wire grid sub-reflector and a polarising main reflector that converts the linearly polarised incidence into circular polarisation with orthogonality between bands. The good performance of the wire grid and the polarising main reflector ensure far-field axial ratio values at the -3 dB region below 1 dB on average without any previous optimisation.

5.      Leri Datashvili, Nikoloz Maghaldadze, Louis Dufour, “Structural Solutions of Deployable Antennas for Small Satellites”, 13th European Conference on Antennas and Propagation, Krakow, 31 March-5 April 2019

Abstract: With the generalization of the use of small satellites for Earth observation and telecommunication missions, there is an increasing need for deployable antennas for small platforms, and in particular deployable reflector antennas. This paper presents different research and development focuses in the field of small densely stowable reflector designs, with surface accuracy allowing their use up to Ka-band

6.      S. Tubau, C. Stoumpos, J.-P. Fraysse, A. Cottin, R. Sauleau, P. Potier and H. Legay, ‘Design of a Compact Four-Way Dual Polarization Orthomode Power Divider for Multiport Radiating Elements’,  13th European Conference on Antennas and Propagation, Krakow, 31 March-5 April 2019.

Abstract: The concept and design of a novel compact power divider exhibiting dual-polarization and its use as a feeder for a Fabry-Perot cavity antenna comprising 4 input ports is presented. The dual and in-phase polarization on each of the four circular waveguides is achieved by using 4 five-port turnstile junctions accompanied by two 8-by-1 power division structures. The power divider ends up to two ports (each for one polarization) so that it can be used as a feeding network for an antenna array. The design is fully metallic, a feature that makes this feeder an ideal candidate for satellite applications. The design band is 3.65 to 3.95 GHz, presenting a Return Loss better than 20 dB and an input-output isolation (orthogonal modes) better than 30 dB. The exciter is further connected to Fabry-Perot cavity antenna and the simulation results of the total feed are presented.

7.      F. M. Sun, M. Jesús Cañavate Sánchez, A. Segneri, Y. Ding, G. Goussetis, S. McLaughlin, “Optimising DVB-S2(X) links in nonlinear environments,” Microwave Theory and Techniques Workshop, ESA – ESTEC, 2-4 April 2019

Abstract: Satellite communication standards such as the second-generation digital video broadcasting for satellites, i.e., DVB-S2(X), exploit phase-shift keying (PSK) and amplitude and phase-shift keying (APSK) modulation schemes as they are more robust against nonlinearity than quadrature amplitude modulations (QAMs). However, the system performance of satellite communication remains profoundly influenced by the presence of the nonlinear high power amplifiers (HPA). In this contribution, we analytically and numerically study the end-to end distortion of the APSK constellation from the digital IQ signal at the transmitter across to the nonlinear channel and back to the recovered digital IQ signal at the receiver. We demonstrate that the distortion depends not only on the input back-off (IBO) of the HPA but, critically, also on the roll-off of the matched digital root raised cosine (RRC) bandwidth-limiting filters used at transmitters and receivers. Consequently, we derive informed guidelines for the adaptive operation of satellite links.

8.      C. Benteyn, E. Fourn, R. Gillard, G. Goussetis, E. Girard, L. Datashvili, 'Réseaux réflecteurs reconfigurables mécaniquement', 21st Journées Nationales Micro-ondes, Caen, France, 14-17 May 2019

Abstract: Plusieurs propositions de concepts ont été étudiées pour la reconfigurabilité d’un réseau-réflecteur que celle-ci soit passive ou active, RF ou mécanique. Un nouveau concept est présenté ici et se base sur la déformation du plan de masse par l’utilisation d’actionneurs. La modification de la distance substrat/plan de masse permet de changer la loi de phase avec un seul panneau réflecteur et offre ainsi une reconfigurabilité mécanique de l’antenne. Dans ce document sont présentées : la modélisation du comportement des cellules réfléchissantes par rapport à la distance substrat/plan de masse et la méthodologie de conception du système global.

9.      S. Mercader Pellicer, G. Goussetis, G.M. Medero, H. Legay, D. Bresciani, N.J.G. Fonseca, “Cross-Polarization Reduction of Linear-to-Circular Polarizing Reflective Surfaces,” IEEE Antennas and Wireless Propagation Letters, Vol. 18, No. 7, pp. 1527-1531, July 2019

Abstract: This letter proposes an efficient design process to reduce the cross-polarization of linear-to-circular reflection polarizers illuminated by practical feeds. In particular, we propose a two-step process, where firstly a geometrical optimization of the unit-cell is applied along one plane of the reflector, followed by a progressive rotation of the unit-cell in the orthogonal plane. An offset flat polarizer comprised of dipole unit-cells and fed by a standard gain horn has been used to illustrate the proposed process. Significant improvements in cross-polarization discrimination are demonstrated by simulation. Two breadboards have been manufactured and their response is compared in order to demonstrate the validity of the design process. Good agreement with measurements is observed corroborating the proposed technique

10.  T. Ströber and M. Ettorre, "2D Physical Optics Analysis of the Focal Region of Parallel-Plate Waveguide Lenses", IEEE International Symposium on Antennas and Propagation and USNC-URSI Radio Science Meeting, Atlanta, USA, 7-12 July 2019

Abstract: A physical optics (PO) method for computing the focal-region fields of a parallel-plate waveguide (PPW) lens is presented. A simplified delay line model is used to represent the delay section between inner and outer lens profile. The lens is analyzed by assuming a plane wave incident on the outer contour. For a given lens geometry, the resulting maximum field loci at different angles of incidence are reported. The close agreement with full-wave results by a commercial simulator validates the applicability of the underlying two-dimensional (2D) lens model. The developed tool is several orders of magnitude faster than the general purpose full-wave simulation and therefore presents an efficient auxiliary tool for the design of lens feed networks.

11.  A. Guarriello, R. Loison, G. Goussetis, D. Bresciani, H. Legay, “Phoenix cells reduced database construction for efficient reflectarray synthesis,” IEEE International Symposium on Antennas and Propagation and USNC-URSI Radio Science Meeting, Atlanta, USA, 7-12 July 2019

Abstract: Reflectarray antennas are becoming a popular technology, in particular for what concerns space applications. In this paper a technique for the synthesis of low profile reflectarray for space application is proposed and demonstrated in the context of an S-band design. It consists of the construction of a reduced bijective database, obtained by selecting a very limited set of Phoenix cells with minimal frequency dispersion. The geometrical continuity requirement between cells presenting close phase shifts has to be ensured as well. This kind of database is particularly applicable to narrowband applications, which would include reflectors for scientific space missions.

12.  S. Tubau, F. Vidal, H. Legay, B. Palacin, G. Goussetis, “Novel Multiple Beam Antenna Farms For Megaconstellations,” 40th ESA Antenna Workshop, ESA-ESTEC, Nordwijk, The Netherlands, 8-10 October 2019

Abstract: Innovative antenna solutions based on quasi-optical beamformers have recently been developed and are identified as competitive antenna contenders for telecommunication systems based on LEO constellations of satellites. They were successfully benchmarked with more conventional antenna solutions. This paper presents a payload of reduced complexity that associates a passive antenna farm producing a 96 beams coverage with isoflux characteristics and beam hopping for introducing flexibility and matching to changing non-uniform user traffic.

13.  S. Mercader-Pellicer, G. Goussetis, D. Bresciani, H. Legay, N.J.G. Fonseca, “Angularly Stable Linear-to-Circular Polarising Reflectors for Multiple Beam Applications,” 40th ESA Antenna Workshop, ESA-ESTEC, Nordwijk, The Netherlands, 8-10 October 2019

We propose a concept to improve the angular stability of reflection linear to circular polarisers. The value of this concept is demonstrated by means of a prototype involving an innovative multibeam antenna architecture. The far-field performance of this prototype is compared by simulation with the performance of another prototype designed without the proposed concept. Improvements by simulation up to 2 dB in the farfield axial ratio (AR) within the 3dB-beamwidth are achieved. A prototype with the proposed concept is also under manufacturing.

14.  L. Bai, C.-X. Wang, Q. Xu, S. Ventouras, G. Goussetis, “Prediction of Channel Excess Attenuation for Satellite Communication Systems at Q-band Using Artificial Neural Network,” IEEE Antennas And Wireless Propagation Letters, Vol. 18, No. 11, pp. 2235-2239, November 2019

Abstract: This paper proposes the use of an artificial neural network (ANN) for estimating the fading of a Q-band (39.402 GHz) satellite channel exploiting knowledge of its previous state as well as the present weather conditions. The ANN is trained using weather data and propagation measurements at Q-band obtained during a period of nine months by the Aldo Paraboni receivers of RAL Space at Chilbolton. Subsequently, the estimation obtained by the ANN is compared with actual propagation measurements on data obtained over a period of three months. Statistical analysis demonstrates agreement between the ANN estimation and the measurement within a 1 dB range with a probability exceeding 98.8%. The significance of this work lies with the opportunities it raises to deliver real-time fading estimations using low-cost weather sensors combined with feedback on the channel state from the return link, which can be used in the deployment of propagation impairment mitigation techniques (PIMTs)

15.  P. Bantavis, C.G. Gonzalez, C. Diallo, R. Sauleau, G. Goussetis, S. Tubau, H. Legay, “All-Metal Graded Index Gutman Lens Antenna - A More Compact Luneburg Lens,” European Conference on Antennas and Propagation (EuCAP), Copenhagen, Denmark, 15-20 March 2020

Abstract: The present work introduces an all-metal Gutman Lens antenna in a parallel plate waveguide (PPW) technology for space applications in Ku band. The novelty of this work as it is compared to the Luneburg Lens is illustrated as follows. It provides up to 35% more compact size compared to the Luneburg. Then, higher number of feeds (single ridge waveguides) are integrated leading to improved overlapping between the patterns. Finally, the matching of the antenna is realized with a 3 step transition from a PPW filed with periodic metal posts to an SMA 50 ohm connector.

16.  C. Stoumpos, J.-P. Fraysse, S. Tubau, G. Goussetis, R. Sauleau and H. Legay, "A Compact and Broadband Four-Way Dual Polarization Waveguide Power Divider for Antenna Arrays," 2020 14th European Conference on Antennas and Propagation (EuCAP), Copenhagen, Denmark, 2020

Abstract: The design and optimization of a novel compact and highly efficient power divider exhibiting dual-polarization in an in-phase 2×4 scheme (4-way) is presented. The two fundamental orthogonal modes TE10 and TE01 arrive in-phase on each of the four square waveguides for each polarization by the utilization of four 3-port turnstile junctions accompanied by four E-plane and two H-plane power division structures. The power divider ends up to two commercial waveguide (WR75) ports (each for one polarization). The presented passive component can be used as a dual-polarized feeding network for a 2×2 antenna array or any four-port radiating element with square input waveguides and aperture sizes above 2.4λ that are commonly targeted for focal array or direct radiating elements at GEO applications. The power divider is fully metallic, a fact that makes it an ideal candidate for satellite applications. The design band is Ku-Tx (10.7-12.75 GHz), presenting a Return Loss better than 20 dB and an input-output isolation of the orthogonal modes better than 30 dB. The exciter is also subjected to sensitivity analysis for estimating its manufacturing tolerances, exhibiting a robust behavior to dimensional variations, while its losses are also evaluated around 0.1 dB when aluminum parts are assumed. Finally, a compact topology of a 2.5λ aperture size array in a 2×2 scheme was designed and optimized where the level of aperture efficiency was the principal design goal. The array is after connected to the exciter to obtain the final feed system.

17.  P. Bantavis, C. Garcia Gonzalez, R. Sauleau, G. Goussetis, S. Tubau, H. Legay, “A broadband graded index Gutman lens with wide field of view utilizing artificial dielectrics – A design methodology,” Optics Express, Vol. 28, Issue 10, pp. 14648-14661, October 2020

Abstract: A novel all-metal graded index Gutman lens is proposed. It exploits an interleaved metasurface unit-cell with glide symmetry that can provide high values of equivalent refractive index with low frequency dispersion. The result is a compact lens with broadband performance and wide field of view up to ±70◦. The proposed lens exhibits low loss, directive beams and is an appealing candidate for space applications. The design approach introduced can be applied to other graded index lenses with circular symmetry using rectangular or circular periodic structures.

18.  F. Vidal, H. Legay, G. Goussetis, T. Ströber, J.-D. Gayrard, “Benchmark of MEO Multibeam Satellite Adaptive Antenna and Payload Architectures for Broadband Systems,” 10th Advanced Satellite Multimedia Systems Conference, 20 – 21 October 2020

Abstract: In the context of a competitive 5G environment, satellite systems must be able to provide cost-effective solutions to complement terrestrial networks. In a preliminary paper, the achievable capacities of diverse LEO satellite payloads were computed as a function of a parameter characterising the non-uniformity of the users distribution in the satellite field of view. As the non-uniformity parameter increases, the capacities of the various payloads benchmarked decrease because of inter-beam interference and shortage of frequency resource. A way to mitigate this capacity loss is to use flexible payloads with adaptive capabilities such as beam steering or flexible resource allocation. This paper proposes to extend the study to MEO payload and antenna architectures and benchmark them with respect to the capacity they can achieve and the power they require. A Circular Direct Radiating Array with Digital Beam Forming, a Sparse Direct Radiating Array with Digital Beam Forming as well as an architecture implementing Hybrid Beam Forming are analysed in terms of effective capacity achieved on different scenarios of users distributions with varying non-uniformities. The application of these results on a realistic scenario of user distribution concludes on the most promising payload architecture

19.  F. Vidal, H. Legay, G. Goussetis, “Joint Power, Frequency and Precoding Optimisation in a Satellite SDMA Communication System,” 10th Advanced Satellite Multimedia Systems Conference, 20 – 21 October 2020

Abstract: State-of-the-art satellite processors include the capacity to offer full digital beamforming. Digital beamforming used jointly with an active antenna allows a full power, frequency and beamforming flexibility. This flexibility must be utilised with efficient and fast computing resource allocation algorithms, especially in a MEO use-case. As MEO satellites move with respect to Earth contrary to GEO satellites, they experience very diverse user distributions and must dynamically adapt the resources allocated to each user. This paper proposes an algorithm based on SDMA which leverages the payload flexibility with a joint power, frequency and beamforming optimisation. The algorithm provides a fair resource allocation to users, accounting for their respective required spectral efficiency

20.  S. Rotenberg, S.K. Podilchak, P.D. Hilario, C. Mateo-Segura, G. Goussetis, J. Lee,” Efficient Rectifier for Wireless Power Transmission Systems,” IEEE Microwave Theory and Techniques, Vol. 68, No. 5, pp. 1921-1932, May 2020

Abstract: This paper describes a full-bridge rectifier and a receiving antenna array for operation within an innovative wireless power transmission (WPT) system. A high-power transmitter using circularly polarized free-space waves and based on retrodirective antenna array technology, is also employed to boost the overall received RF power at the input of the rectenna. To the authors’ best knowledge, the proposed rectifier circuit and active antenna configuration is the first demonstration of a high power beam tracking system for WPT scenarios, being different from previously reported near-field coupling and other lower power harvesting schemes. The main focus of our present work is the rectifier design, its bench-top measurements, and operation in such a retrodirective, self-tracking microwave system. A novel approach based on in-phase multitone input signals is also developed to improve rectifier efficiency. The rectifier size is 4.5 cm by 2 cm and can offer more than 86% and 75% RF-to-DC rectification efficiency at 27 dBm for an input signal at 1.7 GHz and 2.4 GHz, respectively. This rectifier circuit component can also be employed in other communication applications or WPT systems. For example, to convert to dc received RF signals or power in the radiating near- and far-field in order to wirelessly charge the batteries of home electronics such as smartphones, tablets or IoT devices.

21.  A. Costouri, J. Nessel, G. Goussetis, “Validation of a Digital Noise Power Integration Technique for Radiometric Clear Sky Attenuation Estimation at Q-Band,” IEEE Transactions Antennas and Propagation, Vol. 68, No. 9, pp. 6743-6751, Sept 2020

Abstract: This paper presents the validation of a digital signal processing technique that can be used to estimate radiometric sky brightness, and hence, atmospheric absorption, within existing digital receivers at little/no additional cost. To demonstrate this, a receiver was constructed that simultaneously records the beacon signal power from the Alphasat Aldo Paraboni technology demonstration payload, as well as the integrated noise power in the adjacent band. Calibration of the digital radiometer is performed using a combination of hot-cold and tip-curve calibration procedures. Atmospheric fading is then obtained by observing the beacon as well as the radiometric signals. This enables the concurrent estimation and comparison of fading obtained by the two techniques and provides a means to calibrate the received beacon power level to obtain total atmospheric attenuation. It is shown that for low levels of fading, up to a few dB, the two techniques provide good agreement. This approach can therefore provide a low-cost option for geostationary mm-wave satellite channel measurements in the low fading regime, which can be useful in the design and operation of the feeder links in emerging satcom systems.

22.  L. Dufour, L. Datashvili, F. Guinot, H. Legay, G. Goussetis, " Origami Deployable Reflector Antenna for CubeSats,” American Institute of Aeronautics and Astronautics (AIAA) SciTech 2021 Forum, 11–15 & 19–21 January 2021 

Abstract: Compact, deployable reflector antennas on CubeSats are now a key enabling technology for many telecommunication and scientific missions. This paper presents a novel concept for center-fed deployable reflector antennas for CubeSat using carbon-fiber reinforced elastomer materials and origami techniques for doubly-curved surfaces, called the roll-ribs reflector concept. The origami design methodology and the reflector concept optimization process are illustrated through the design of a 0.5 m, Ka-band front-fed Cassegrain reflector antenna folding into 1.3 U, with a deployable origami reflector and a deployable subreflector. The reflector antenna concept presented in this paper uses the FlexRS® materials family developed by Large Space Structures GmbH, and the origami folding methodology is coined OriFlex®. A demonstrator is built and tested for folding and deployment, and RF performance.

23.  F. Vidal, H. Legay, G. Goussetis, M. Garcia Vigueras, S. Tubau, J.-D. Gayrard,”A Methodology to Benchmark Flexible Payload Architectures in a Megaconstellation Use-case,” International Journal of Satellite Communications and Networking, Vol. 39, No. 1, pp. 29-46, January 2021

Abstract: This paper proposes a methodology to benchmark satellite payload architectures and find the optimal trade-offs between high flexibility and low complexity. High flexibility would enable the satellite to adapt to various distributions of user terminals on the ground and fulfill the data rate demand of these users. Besides, low complexity is required to keep satellite networks competitive in the context of emerging 5G networks. To estimate the flexibility of a payload, an indicator to characterize the non-uniformity of user distributions is proposed. Each benchmarked payload may be characterized by a graph relating the throughput to this parameter further denoted µ. The payload provides the same throughput trends for different scenarios of user distributions with the same µ parameter. As a consequence, the average capacity of the system may be estimated by i) calculating the probability distribution of µ over the orbit, ii) integrating the throughput based on this payload response. It thus results in a straightforward way for benchmarking payloads directly on an estimation of the averaged capacity, accounting for the user distribution over the earth. A simulation platform has been developed to characterize the payload throughput including the implementation of a resource allocation algorithm that accounts for constraints of various payloads. Using this definition and the developed tool, we benchmark a bent-pipe architecture, a beam hopping architecture and a hybrid beam-steering architecture for a LEO megaconstellation use case. The methodology showcases the interest for investigating different payload architectures depending on realistic traffic scenario analysis.

24.  F. Vidal, H. Legay, G. Goussetis, J-P. Fraysse, "Joint Precoding and Resource Allocation Strategies Applied to a Large Direct Radiating Array for GEO Telecom Satellite Applications,” European Conference on Antennas and Propagation (EuCAP), 22-26 March 2021

Abstract: The ever-rising demand for very high throughput satellites drives the requirements toward larger antennas benefiting from increased directivities and narrower beams. Narrow beams allow frequency reuse across the coverage and capacities as high as Tbps can be achieved. To flexibly allocate this capacity, an active deployable direct radiating array is an attractive solution with power flexibility and in-orbit coverage reconfiguration. This solution, however, requires very high numbers of radiating elements compared to more conventional reflector based solutions. Moreover, digital only beamforming is power hungry due to the processing of large frequency bandwidths for each radiating element. Novel beamforming approaches must be investigated to save onboard power. A hybrid beamforming architecture based on analog beamforming at sub-array level and digital beamforming reduces the power consumption of the digital core. A disadvantage of hybrid beamforming is the appearance of grating lobes in the satellite field of view. A system approach to mitigate grating lobes is proposed. This strategy is based on the joint use of precoding and smart resource allocation. The impact of the non-uniformity of users distributions on capacity is also assessed

25.  C. Stoumpos, J.-P. Fraysse, G. Goussetis, R. Sauleau, C. G. González, T. Pierré and H. Legay, "Four-Way Orthomode Waveguide Power Dividers: Subtractive and Additive Manufacturing," 15th European Conference on Antennas and Propagation (EuCAP), 22-26 March 2021

Abstract: This paper presents two waveguide power dividers in a planar 4-way equiphasic dual-polarization power division configuration operating in the transmit Ku-band (10.7-12.75 GHz). Both concepts are primarily targeted as excitation networks for multiple accesses radiating elements or antenna arrays. The presented solutions are characterized by two different variants that accommodate for different manufacturing processes, namely subtractive manufacturing (SM) and additive manufacturing (AM). Their principal operations are described and finally their RF performance is presented and compared experimentally inter alia. The principal objective is to demonstrate the mechanical complexity of this type of microwave components and how 3Dprinting enables its efficient realization via co-design.

26.  C. Stoumpos, J.-P. Fraysse, G. Goussetis, R. Sauleau, C. G. González and H. Legay, "Compact and Highly Efficient Single and Dual Polarized Aperture Antennas with Integrated Multiport Overmoded Excitation," 15th European Conference on Antennas and Propagation (EuCAP), 22-26 March 2021

Abstract: This paper presents a new type of radiating horn-like radiating element which exploits a two- or four-port integrated overmoded power division depending on the aperture type and the requirement for single- or dual polarization. The general concept is illustrated by two design examples which are proposed in this paper at Ku-Tx band (10.7 – 12.75 GHz); a single-polarized two-access rectangular aperture pyramidal horn and a dual-polarized four-access square aperture horn feed antenna. The generic operational principles call for a power divider which feeds two or four suitably flared waveguide sections which are further connected to a bi- or quad-furcated surface discontinuity for the combination of the incoming fields. Finally, a common waveguide region on top completes the total topology. This type of radiating elements exhibits a compact profile, while at the same time achieves high aperture efficiency (over 90%) due to robust materialization of the desired aperture modal content over a bandwidth of 20%.

27.  T. Ströber, M. Ettorre, G. Goussetis, H. Legay, S. Tubau, “A Parallel-Plate Lens for Mechanical Wide-Angle Beam Scanning,” 15th European Conference on Antennas and Propagation (EuCAP), 22-26 March 2021

Abstract: This paper presents a parallel-plate waveguide lens for wide-angle mechanical beam steering. A previously developed ray-tracing procedure is used for designing the quasi-optical system. The feed system is based on gap waveguide technology enabling a simple and rapid mechanical actuation. Validation of the proposed concept is given by numerical results for a Ka-band lens design. A high scanning performance over an angular range of +− 50◦ with a worst-case scan loss of about 3 dB is achieved. The simulated return loss is greater than 15 dB in the 27.5–31 GHz band. The proposed lens beamformer is an attractive ground segment solution for future Satcom applications

28.  F. Vidal, H. Legay, G. Goussetis, A. Segneri, “A System Approach to enable Digital Beamforming with Direct Radiating Arrays: the joint use of Precoding and Sparse Arrays,” International Journal of Satellite Communications and Networks, in press

Abstract: Digital beamforming with an active array antenna has become, these past years, the holy grail for flexible satellite payloads. This architecture enables a power, frequency and beam steering flexibility that meets the requirements of a wide range of user terminal distributions. Matching these distributions may be challenging, especially if user terminals are co-located. In this case, narrower beams are needed to utilize high frequency reuse factors while avoiding interbeam interference. Small beamwidths, however, require large antenna diameters, which implies for conventional antenna arrays many radiating elements and subsequently an increased complexity. A way to reduce the number of radiating elements is to resort to sparse arrays with an irregular layout of radiating elements. A disadvantage of this type of antenna is their high side lobe levels when scanning the beams. A robust on-board precoding strategy based on the knowledge of the users’ positions, and the antenna gain over the coverage, is proposed to mitigate the interference arising from high side lobe levels. A Circular Direct Radiating Array and a Sparse Direct Radiating Array based on a sunflower design are compared with respect to the sum rates they can achieve, and the complexity of the processor required to perform full digital beamforming

29.  T. Ströber, S. Tubau, E. Girard, H. Legay, G. Goussetis, M. Ettorre, “Shaped Parallel-Plate Lens for Mechanical Wide-Angle Beam Steering,” IEEE Transactions Antennas and Propagation, in press

Abstract: A parallel-plate lens beamformer for continuous wide-angle scanning is presented. The design is based on a compact two-lens system with extended scanning range. An optimization process based on a previously developed geometrical optics technique is used to shape the quasi-optical system. The mechanical feed system relies on the non-contact characteristic of groove gap waveguides, offering large bandwidth, low profile and mechanical ruggedness. The proposed concept is validated with an all-metal prototype of a 20.5-λ lens operating in the uplink Ka-band (27.5 – 31 GHz). Good agreement between the simulated and measured performance is obtained. The return loss is greater than 12 dB over the entire frequency band and beyond. The measured broadside gain is 24 dB at the design frequency of 29.25 GHz and the scan loss is about 2.7 dB when scanning out to 50° (14 beamwidths). A good pattern stability is achieved over the entire frequency band. The estimated radiation efficiency ranges from 78 to 91%, depending on the feed position. The proposed beamformer presents a promising ground-segment solution for future Ka-band satellite applications.

30.  T. Ströber, H. Legay, G. Goussetis, M. Ettorre, “Multiple-Beam Synthesis for Shaped Parallel-Plate Waveguide Lenses,” IEEE Antennas and Wireless Propagation Letters, submitted

Abstract: This letter describes a design method for shaped parallel-plate lenses with enhanced scanning range. Conjugate field matching is employed to derive optimal feed contours for a lens with an analytically defined shape, thus avoiding timeconsuming optimization procedures. A previously proposed raytracing technique and physical optics (PO) are used to determine the focal-region distribution on receive. Numerical results for a lens with an aperture of 20λ demonstrate a scanning range of +− 40° (13 beamwidths) with scan losses below 1.4 dB and sidelobe levels below –14 dB. Full-wave simulations validate the proposed design concept.

31.  P.D. Hilario Re, D. Comite, S.K. Podilchak, C.A. Alistarh, G. Goussetis, M. Sellathurai, J. Thompson, J. Lee, “FMCW Radar with Enhanced Resolution and Processing Time by Beam Switching,” IEEE Open Journal Of Antennas And Propagation, in press

Abstract: We present the design of a novel K-band radar architecture for short-range target detection. Applications include direction finding systems and automotive radar. The developed system is compact and low cost and employs substrate-integratedwaveguide (SIW) antenna arrays and a 4×4 Butler matrix (BM) beamformer. In particular, the proposed radar transmits a frequency modulated continuous-wave (FMCW) signal at 24 GHz, scanning the horizontal plane by switching the four input ports of the BM in time. Also, in conjunction with a new processing method for the received radar signals, the architecture is able to provide enhanced resolution at reduced computational burden and when compared to more standard single-input multipleoutput (SIMO) and multiple-input multiple-output (MIMO) systems. The radar performance has also been measured in an anechoic chamber and results have been analyzed by illuminating and identifying test targets which are 2◦ apart, while also making comparisons to SIMO and MIMO FMCW radars. Moreover, the proposed radar architecture, by appropriate design, can also be scaled to operate at other microwave and millimeterwave frequencies, while also providing a computationally efficient multi-channel radar signal processing platform.

32.  M.V. Kuznetcov, S.K. Podilchak, M. Poveda-Garcıa, P. Hilario, C.A. Alistarh, G. Goussetis, J.L. Gomez-Tornero, “Planar Dual-Frequency SIW Leaky-Wave Antenna with Broadside Radiation for CubeSat Applications,” IEEE Antennas and Wireless Propagation Letters, submitted

Abstract: This letter presents a substrate-integrated waveguide (SIW) leaky-wave antenna (LWA) for CubeSat applications. The antenna utilizes middle-point feeding and shorting walls to achieve broadside radiation in the far-field at two distinct frequencies. In particular, this dual-frequency behavior is related to the transition from a pure leaky-wave (LW) at lower frequencies (with a relatively higher leakage radiation rate), to hybrid radiation (at higher frequencies) due to LW radiation and structure resonance. This higher-frequency response is generated by the shorting vias at the lateral ends of the SIW antenna and a lower LW attenuation constant. Given these conditions, the developed prototype is well matched (jS11j ≤ -10 dB) from 23.2 to 23.5 GHz and 24.8 to 25.2 GHz with realized gains of 8 dBi and 6 dBi, respectively. Maximum efficiency (including connector) is around 87%. Such dual-frequency operation could enable uplink and down-link operation in the K-band. Overall dimensions of the antenna are 2λ0 x 2.6λ0 (at the lower frequency). Possible placement on CubeSats can be underneath solar panels, thus increasing the available surface area for solar power harvesting. Also, to the best knowledge of the authors, no similar dualfrequency SIW-LWA has been previously reported

33.  C. Stoumpos, J.-P. Fraysse, G. Goussetis, R. Sauleau, C. G. González and H. Legay, "A Highly Efficient Broadband Pyramidal Horn Antenna with Integrated Power Division," IEEE Transactions on Antennas and Propagation, submitted

Abstract: The concept and development of a highly efficient pyramidal horn is presented here. The radiating element comprises a rectangular radiating aperture fed by two smaller flared square waveguide sections via a bifurcated H-plane surface discontinuity. For the simultaneous feeding of the 2-port radiating element, the total antenna includes a compact H-plane power divider. Design principles are given and illustrated by means of an example involving an antenna with aperture size of about 2.8λ0×1.4λ0 (λ0 being the free-space wavelength at the central frequency of operation). The antenna exhibits very high aperture efficiency levels (above 95%) over the entire Ku-Tx band (10.7 – 12.75 GHz), as well as a compact profile (4.1λ0). The measured results of the prototype manufactured through milling verify experimentally the performance predicted numerically.

34.  M. Sun, G. Goussetis, K. Xu, Y. Ding, S. McLaughlin, A. Segneri, M.J. Canevate Sanchez, “Joint Digital Analogue DVB-S2(X) Link Optimization in Non-linear Channel,” IEEE Transactions on Broadcasting, submitted

Abstract: Future broadband satellite communication (SatCom) systems require high throughput of data transmission, which calls for higher frequency band operations. Adaptive coding and modulation (ACM) has been considered as a means to obtain further performance improvement at these frequencies. However, ACM in the current DVB-S2 and DVB-S2(X) standards does not take into account the effects that arise from the non-linear link with memory, which is generated by the combination of the high-power amplifier (HPA) and the digital root raised cosine (RRC) filters. This paper transfers the non-linear characteristics of the SatCom link into an equivalent full-linear link with an additive noise source for BER analysis. With this equivalent modeling, an approach of selecting/adapting the optimum coding, modulation scheme and associated system configurations for a given channel fading level is proposed. Both simulation and measurement performance are presented to validate the proposed method.

35.  A. Guariello, D. Bresciani, R. Loison, H. Legay, “Structural/RF co-design and optimization of a 6m deployable contour beam double circular polarization reflectarray in S-band,” IEEE Transactions Antennas and Propagation, in preparation

Abstract: This paper presents a feasibility study, the design and analysis of large flat panels deployable RAs. More in particular, it details the coupled mechanical/RF design of a 6 m 9 facets RA that withstand severe thermal gradient along the RA thickness. The RA mechanical/RF coupled design is performed for two configurations surveyed, i.e., a self-standing deployable RA, subject to severe TED deformation, and a mechanically supported low profile RA, more thermoelastically stable. The RF design of the deployable RA is addressed in order to obtain comparable performances with respect to a reference 6 m metallic reflector previously designed, and which would be not suitable to be stowed in the launcher fairing. The performances are evaluated with respect to the far-field components on the Co-polarization and X-polarization for a RA working in double circular polarization (Tx-Rx)

R. Joshi, E. Faridah Nor Mohd Hussin, P. Jack Soh, M. Faizal Jamlos, H. Lago, A. Abdullah Al-Hadi, S.K. Podilchak, “Dual-Band, Dual-Sense Textile Antenna With AMC Backing for Localization Using GPS and WBAN/WLAN,” IEEE Access, Vol. 8, 2020

Abstract: A wearable textile antenna with dual-band and dual-sense characteristics is presented in this work. It operates at the 2.45 GHz band for WBAN and WLAN applications, and at the 1.575 GHz band for Global Positioning System (GPS) applications. An antenna backing based on an artificial magnetic conductor (AMC) plane operating at 2.45 GHz band is introduced to reduce the backward radiation and to improve antenna gain. It consists of a 3×3 array of square patch unit cells, where each unit cell is integrated with four square slits and a square ring. A square-shaped patch is then located on top of the substrate as its radiator. To enable dual-band operation, two corners of this radiator are truncated, with each of the four corners incorporated with a rectangular slit to enable its circular polarization characteristic in the GPS band. Simulation and experimental results are in good agreement and indicate proper antenna operation with linear polarization in the 2.45 GHz band and circular polarization in the 1.575 GHz band, with realized gain of 1.94 dBi and 1.98 dBic, respectively.

1.   .   D.R. Prado, J.A Lopez-Fernandez, M. Arrebola, G. Goussetis, “On the Use of the Angle of Incidence in Support Vector Regression Surrogate Models for Practical Reflectarray Design,” IEEE Transactions Antennas Propagation, Vol. 69, No. 3, pp. 1787-1792, March 2021

Abstract: A common approach in the literature when obtaining surrogate models of reflectarray unit cells is to include, among other variables, the angles of incidence as input variables to the model. In this work, we use support vector regression (SVR) to compare this approach with a new strategy which consists in grouping the refletarray elements under a small set of angles of incidence and train surrogate models per angle of incidence pair. In this case, the dimensionality of the SVR decreases in two with regard to the former approach. In both cases, two geometrical variables are considered for reflectarray design, obtaining 4-D and 2-D SVRs, respectively. In contrast to the common approach in the literature, the comparison between the 4-D and 2-D SVRs shows that a proper discretization of the angles of incidence is more competitive than introducing the angles as input variables in the SVR. The 2-D SVR offers a shorter training time, faster reflectarray analysis, and a similar accuracy than the 4-D SVR, making it more suitable for design and optimization procedures.

Prediction of Channel Excess Attenuation for

Satellite Communication Systems at Q-band Using

Artificial Neural Network

Lu Bai, Cheng-Xiang Wang, Fellow, IEEE, Qian Xu, and Spiros Ventouras, George Goussetis, Senior

Member, IEEE