Scientific Publications

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expandTemperature-dependent Characterization of Power Amplifiers Using an Efficient Electrothermal Analysis Technique
P. Taghikhani, K. Buisman, M. Versleijen, J.-R. Perez-Cisneros and C. Fager; IEEE Transactions on Microwave Theory and Techniques. December 2021

Abstract: In this paper, we propose an efficient methodology for the electrothermal characterization of power amplifier (PA) integrated circuits. The proposed electrothermal analysis method predicts the effect of temperature variations on the key performances of PAs, such as gain and linearity, under realistic dynamic operating conditions. A comprehensive technique for identifying an equivalent compact thermal model, using data from 3-D finite element method thermal simulation and nonlinear curve fitting algorithms, is described. Two efficient methods for electrothermal analysis applying the developed compact thermal model are reported. The validity of the methods is evaluated using commercially available electrothermal computer-aided design (CAD) tools and through extensive pulsed RF signal measurements of a PA device under test. The measurement results confirm the validity of the proposed electrothermal analysis methods. The proposed methods show significantly faster simulation speed comparing to available CAD tools for electrothermal analysis. Moreover, the results reveal the importance of electrothermal characterization in the prediction of the temperature-aware PA dynamic operation.


expandDevelopment of innovative substrate and embedding technologies for high frequency applications
D. Manessis, S. Kosmider, L. Boettcher, M. Seckel, K. Murugesan, U. Maaß, I. Ndip, A. Ostmann, R. Aschenbrenner, M. Schneider-Ramelow, K-D. Lang; 23rd European Microelectronics and Packaging Conference & Exhibition (EMPC). Online. September 2021

Abstract: This paper brings into light all the new developmental work performed in the wide domain of high frequency PCBs for the realisation of innovative metasurfaces at 5GHz as well as compact highly integrated 5G antenna-in-modules at 40 GHz. There is a fast growing demand in high frequency market that justifies the intense R&D work also on microwave and especially mmWave technologies, comprising both “beyond the state-of-the-art high frequency PCBs” and advanced PCB integration concepts. In this context, this paper intends to highlight new knowledge in materials, processes as well as thermal dissipation concepts, that have been derived from various R&D projects, but especially in the framework of the FET-EU “Visorsurf” and the EU-Serena projects. In specific, R&D work will be shown on the emerging concepts of metamaterials that can be software programmable and adapt their properties. The Visorsurf main objective is the development of a hardware platform, the Hypersurface, whose electromagnetic behavior can be programmatically defined. The key enablers for this are the metasurfaces whose electromagnetic properties depend on their internal structure. The Hypersurface hardware platform will be a 4-layer build-up of high frequency PCB substrate materials with the metasurfaces on the top and custom electronic controller nodes at the bottom of the PCB hardware platform. This paper will elaborate on how innovative PCB processes have been tailored to high frequency substrates for the manufacturing of the first 4-layer Hypersurface PCB hardware platform with a size of 300mmx300mm. In a complimentary way, the paper will describe in detail new chip embedding concepts in the same family of high frequency PCB substrates toward the realization of highly miniaturized advanced packages for 5G mmWave applications at 40 GHz. These concepts show vividly the potential of PCB embedding technologies as the mean for heterogeneous integration in high frequency advanced packages/modules. The paper discusses in detail all process chain developments in high frequency PCBs for the embedding of GaN and SiGe chips in PCBs, their interconnection path concept, the embedding of passives, the fabrication of the antenna module and its stacking on a high power or low power PCB module for the final formation of a 6-layer antenna-in-module package which could be separately assembled on the system board. Furthermore, the paper will present for the first time innovative thermal dissipation concepts for the “Serena” antenna module, with the prevailing scenario of thermal vias to the bottom of the GaN and SiGe chips for direct heat removal. All processes for realization of high frequency substrates and embedded 5G 40 GHz antenna modules will be discussed in detail.


expandE/W-Band CPW-based Amplifier MMICs Fabricated in a 60 nm GaN-on-Silicon Foundry Process
R. Malmqvist, R. Jonsson, A. Bernland, M. Bao, R. LeBlanc, K. Buisman, C. Fager, K. Andersson; European Microwave Integrated Circuits Conference 2020. Utrecht/The Netherlands. January 2021

Abstract: This paper presents an experimental evaluation of two co-planar waveguide (CPW) based E/W-band amplifier MMICs realised in a 60 nm GaN-on-Si foundry process. A onestage amplifier and a two-stage amplifier realised in this process have a measured maximum gain of 8 dB and 16 dB at 73-74 GHz, respectively. The two amplifiers have a measured gain of 3 dB and 7 dB at 93 GHz when the drain voltage (Vd) is 10 V and the drain current (Id) is 15 mA per stage. The two-stage amplifier has a measured noise figure (NF) of 2.7-3.8 dB and 2.9-4.1 dB at 90-95 GHz when the Id is 10 mA and Vd is 5 V and 10 V, respectively. The measured NF of this amplifier is equal to 4-6 dB at 92-95 GHz when an Id of 10-20 mA is used in each stage with same drain bias.


expandImplementation Challenges and Opportunities in Beyond-5G and 6G Communication
U. Gustavsson, P. Frenger, C. Fager, T. Eriksson, H. Zirath, F. Dielacher, C. Studer, A. Pärssinen, R. Correia, J. N. Matos, D. Belo, N. B. Carvalho; IEEE Journal of Microwaves. Online. January 2021

Abstract: As 5G New Radio (NR) is being rolled out, research effort is being focused on the evolution of what is to come in the post-5G era. In order to meet the diverse requirements of future wireless communication in terms of increased capacity and reduced latency, technologies such as distributed massive Multiple-Input Multiple-Output (MIMO), sub-millimeter wave and Tera-hertz spectrum become technology components of interest. Furthermore, to meet the demands on connectivity anywhere at anytime, non-terrestrial satellite networks will be needed, which brings about challenges both in terms of implementation as well as deployment. Finally, scaling up massive Internet-of-Things (IoT), energy harvesting and Simultaneous Wireless Information and Power Transfer (SWIPT) is foreseen to become important enablers when deploying a large amount of small, low-power radios. In this paper, we will discuss some of the important opportunities these technologies bring, and the challenges faced by the microwave and wireless communication communities.



expandA Novel Packaging and System-Integration Platform with Integrated Antennas for Scalable, Low-Cost and High-Performance 5G mmWave Systems
I. Ndip, K. Andersson, S. Kosmider, T. Le, A. Kanitkar, M. van Dijk, K. Murugesan, U. Maaß, T. Löher, M. Rossi, J. Jaeschke, A. Ostmann, R. Aschenbrenner, M. Schneider-Ramelow, K. Lang; 2020 IEEE 70th Electronic Components and Technology Conference (ECTC 2020) . Online. June 2020

Abstract: In this work, we present a novel packaging and system-integration platform with integrated antennas (antenna-in-package, AiP, platform) for 5G millimeterwave (mmWave) systems. We illustrate the application of the platform for the development of miniaturized, scalable, low-cost and high-performance 5G mmWave systems for new radio (NR) base stations. RF characterization of the dielectric material of the platform and the integrated mmWave antennas as well as thermal investigations of the platform are presented. The process steps required for the fabrication of the platform are discussed, and an example of a mmWave chip embedded in the platform is shown.


expandPCB Embedding Technology for 5G mmWave Applications
Stefan Kosmider, Kavin Murugesan, Te Huyen Le, Uwe Maaß, Marco Rossi and Lars Boettcher; 16th Annual Device Packaging Conference (DPC 2020) . Fountain Hills/Arizona/USA. March 2020

Abstract: The roll out of 5G networks has already started worldwide and in the near future it is expected to dramatically reshape the wireless communication landscape. Nevertheless, a number of technical challenges still need to be addressed in the most recent packaging development approaches, such as the implementation of a large number of connections at high data rates, exhibiting high gain to compensate for the high free space loss at millimeter wave frequencies. Within the European funded project SERENA, partners from academia, research and industry are collaborating to address these topics and develop an integration platform, based on PCB embedding technology, capable of reducing size, power consumption and design time and complexity, while at the same time achieving increased performance, energy efficiency and transmitted output power. In particular, PCB embedding technology offers the potential to realize an integrated RF electronics module containing ICs for RF signal generation and antennas with very short interconnects in a single package, thus minimizing the signal path losses. In the framework of the SERENA project, new RF materials suitable for the embedding of components are applied in combination with high gain GaN and SiGe dies for the first time to implement a scalable System-in-Package operating at 39 GHz.


expandMulti-Physical Simulations and Modelling of an Integrated GaN-on-Si Module Concept for Millimetre-Wave Communications
Rasilainen, Kimmo; Buisman, Koen; Andersson, Kristoffer; Fager, Christian; 2020 IEEE 70th Electronic Components and Technology Conference. Online. June/July 2020

Abstract:This paper presents a multi-physical system-level simulation workflow to characterise the performance of a heterogeneously integrated communications module for mm-wave applications. Basic principles behind modelling different parts and properties of the module are explained. The workflow combines the electromagnetic properties of a patch antenna array operating at 39GHz with polynomial-based power amplifier (PA) models and thermal simulations of the structural heating. Effects of heating on the PA properties are also considered. The PA model is based on and compared with circuit simulations of a mm-wave transceiver chip, and the results are in good agreement. The proposed workflow can be used to describe and predict the performance of the module in different spatio-temporal use cases, and the approach also scales to larger arrays and more detailed simulation models.


expandOptimising GaN heterostructures for 5G
Markus Behet, Joff Derluyn, Stefan Degroote, Marianne Germain; Article in Compound Semiconductor Magazine. February 2020

Abstract:THE ROLL-OUT of 5G is great news for GaN. It is predicted to propel the market for RF devices made from this wide bandgap semiconductor to more than $2 billion by 2024, according to the French market analyst Yole Développement. The move from 4G to 5G should be seen as part evolution, part revolution. Grabbing the most attention is the availability of enhanced mobile services, resulting from faster speeds, ultra-low latency, and a reduction in power consumption. However, 5G will also bring further investment in traditional machineto-machine and internet-of-things applications, and open up new market opportunities in mission critical services, such as autonomous vehicles, drones and ‘telehealth’. It is even expected that 5G will act as a catalyst for transformative changes of work processes, and will establish a new set of rules for competitive economic advantages. So great are these changes that IHS Markit forecasts 5G to enable $13.2 trillion of global economic output in 2035.


expandPerformance Simulation of a 5G Hybrid Beamforming Millimeter-Wave System
Thomas Kühne, Xiaoshen Song, Giuseppe Caire, Kimmo Rasilaineny, Thi Huyen Lez, Marco Rossiz, Ivan Ndipz, and Christian Fager; International ITG Workshop on Smart Antennas (WSA 2020), Hamburg, Germany. February 2020

Abstract:Millimeter-wave systems are the next step to increase the data rate of 5G mobile communication networks. Hybrid analog-digital beamforming is one of the core technologies to enable millimeter-wave communication. Both the theoretical basics and the hardware design have been investigated in recent years. Current research projects like the European SERENA project strive to develop platforms to demonstrate the performance gain of complete systems. We present a simulation based analysis of a planned proof-of-concept system to evaluate the influence of design decisions and hardware impairments. We use a geometrybased stochastic channel simulator and simulate both certain hardware aspects and signal processing parts. We focus on the signal processing parts directly related to the hybrid architecture used for multi user MIMO precoding like the initial link acquisition and the data precoding. We use our own state-ofthe-art algorithms for these parts.



expandFully-/Partially-Connected Hybrid Beamforming Architectures for mmWave MU-MIMO
Xiaoshen Song, Thomas Kühne, Giuseppe Caire; Journal paper, published in IEEE Transactions on Wireless Communications in December 2019

Abstract:Hybrid digital analog (HDA) beamforming has attracted considerable attention in practical implementation of millimeter wave (mmWave) multiuser multiple-input multiple-output (MU-MIMO) systems due to the low power consumption with respect to its fully digital baseband counterpart. The implementation cost, performance, and power efficiency of HDA beamforming depends on the level of connectivity and reconfigurability of the analog beamforming network. In this paper, we investigate the performance of two typical architectures that can be regarded as extreme cases, namely, the fully-connected (FC) and the one-stream-per-subarray (OSPS) architectures. In the FC architecture each RF antenna port is connected to all antenna elements of the array, while in the OSPS architecture the RF antenna ports are connected to disjoint subarrays. We jointly consider the initial beam acquisition and data communication phases, such that the latter takes place by using the beam direction information obtained by the former. We use the state-of-the-art beam alignment (BA) scheme previously proposed by the authors and consider a family of MU-MIMO precoding schemes well adapted to the beam information extracted from the BA phase. We also evaluate the power efficiency of the two HDA architectures taking into account the power dissipation at different hardware components as well as the power backoff under typical power amplifier constraints. Numerical results show that the two architectures achieve similar sum spectral efficiency, while the OSPS architecture is advantageous with respect to the FC case in terms of hardware complexity and power efficiency, at the sole cost of a slightly longer BA time-to-acquisition due to its reduced beam angle resolution.



expandAn Analog Module for Hybrid Massive MIMO Testbeds Demonstrating Beam Alignment Algorithms
Thomas Kühne, Giuseppe Caire, International ITG Workshop on Smart Antennas (WSA 2018), Bochum, Germany. March 2018.

Abstract:Hybrid analog-digital beamforming for massive MIMO is an important technology for millimeter-wave communication systems. Current experimentation of massive MIMO is based mainly on full digital solutions and in the sub-6 GHz frequency range. The technology for millimeter-wave massive MIMO systems is not yet available to the broad research community. Due to high path loss, sparsity of the channel, and restrictions of the hardware in the millimeter-wave band, new challenges in signal processing arise. One of these problems is the initial link acquisition also called beam alignment (BA). We present a hybrid analog-digital massive MIMO sub-6 GHz testbed with 64 antennas. This testbed enables the investigation of challenges connected to a hybrid analog-digital architecture like the BA problem. We demonstrate multiple BA algorithms to show their advantages and disadvantages. The testbed is based on a self-developed analog module with a high resolution of phase and amplitude settings. Our module can be connected to standard software defined radios (SDRs) and supports different types of hybrid architectures


expandFully-Connected vs. Sub-Connected Hybrid Precoding Architectures for mmWave MU-MIM
Xiaoshen Song, Thomas Kühne, Giuseppe Caire; arxiv version of the ICC conference paper, October 2018

Abstract:Hybrid digital analog (HDA) beamforming has attracted considerable attention in practical implementation of millimeter wave (mmWave) multiuser multiple-input multiple-output (MU-MIMO) systems due to its low power consumption with respect to its digital baseband counterpart. The implementation cost, performance, and power efficiency of HDA beamforming depends on the level of connectivity and reconfigurability of the analog beamforming network. In this paper,weinvestigatetheperformanceoftwotypicalarchitectures for HDA MU-MIMO, i.e., the fully-connected (FC) architecture where each RF antenna port is connected to all antenna elements of the array, and the one-stream-per-subarray (OSPS) architecturewheretheRFantennaportsareconnectedtodisjoint subarrays. We jointly consider the initial beam acquisition phase and data communication phase, such that the latter takes place by using the beam direction information obtained in the former phase. For each phase, we propose our own BA and precoding schemes that outperform the counterparts in the literature. We also evaluate the power efficiency of the two HDA architectures taking into account the practical hardware impairments, e.g., the power dissipation at different hardware components as well as the potential power backoff under typical power amplifier (PA) constraints. Numerical results show that the two architectures achievesimilarsumspectralefficiency,buttheOSPSarchitecture outperforms the FC case in terms of hardware complexity and power efficiency, only at the cost of a slightly longer time of initial beam acquisition.