Search

Information and communication technologies (ICT) are the foundation of growth and development in the modern global economy. They are striving to bring robust connectivity to all corners of the globe, driving both innovation and ways in which technologies can be used to improve economic and social development towards a smart society. New means of connectivity plus enhanced architectures promise improved coverage, greater capacity, higher data rates, more efficient use of spectrum resources, lower latency, higher system reliability, and more flexibility for effective provision of information and communication services. These activities can be summarized under the development of the 5th generation of mobile communication systems (5G). Innovative wireless technologies will be a key component in this development, which allow new applications summarized under the term of Internet of Everything including the Internet of Things (IoT), Machine-to-Machine (M2M) communications, smart cities, smart manufacturing, intelligent transportation systems, and inter-connected cars. Key differentiators of 5G to provide future wireless connectivity are: (1) 10-fold decrease in latency down to 1 ms, (2) 10-fold data throughput with multi-Gbps peak rates, and (3) 100-fold traffic capacity, e.g. by network densification with local femto cells. Efficiency is one major aspect within the development of 5G systems with massively deployed new communication nodes. To advance beyond conventional terrestrial 4G communication systems such as Long Term Evolution (LTE) and LTE-Advanced, groundbreaking disruptive systems and hardware concepts are required to comply with all promises by 5G.

A finite element method (FEM)-based simulation approach to predict the tunability in composite materials was developed and tested with analytical data. These tests showed good prediction capabilities of the simulation for the test data. The simulation model was then used to predict the tunability of a network-structured composite, where the dielectric phase formed clusters in a paraelectric network. This was achieved by simulating a reciprocal core-shell unit cell of said network. The simulation showed a high tunability for this network model, exceeding the tunability of the analytically evaluated layered, columnar, and particulate model. The simulation results were experimentally verified with a Ba₀.₆Sr₀.₄TiO₃/Mg₃B₂O₆ (BST/MBO) composite, where core-shell granulates were made with a two-step granulation process. These structured samples showed higher tunability and dielectric loss than the unstructured samples made for comparison. Overall, the structured samples showed higher tunability to loss ratios, indicating their potential for use in tunable radio frequency applications, since they may combine high performance with little energy loss.

This work presents a method for reducing acoustic resonances in ferroelectric barium strontium titanate (BST)-based bulk ceramic varactors, which are capable of operation in high-power matching circuits. Two versions of parallel-plate varactors are manufactured here: one with pure BST and one with 10 vol-% magnesium borate, Mg₃B₂O₆ (MBO). Each varactor includes a 0.85-mm-thick ferroelectric layer. Acoustic resonances that are present in the pure BST varactor are strongly suppressed in the BST-MBO varactor and, hence, the Q-factor is increased over a wide frequency range by the addition of small amounts of a low-dielectric-constant (LDK) MBO. Although the tunability is reduced due to the presence of non-tunable MBO, the increased Q-factor extends the varactor’s availability for low-loss and high-power applications.

Modern communication platforms require a huge amount of switched RF component banks especially made of different filters and antennas to cover all operating frequencies and bandwidth for the targeted services and application scenarios. In contrast, reconfigurable devices made of tunable components lead to a considerable reduction in complexity, size, weight, power consumption, and cost. This paper gives an overview of suitable technologies for tunable microwave components especially for SatCom applications. Special attention is given to tunable components based on functional materials such as barium strontium titanate (BST) and liquid crystal (LC).

In this paper, the gap waveguide technology is examined for packaging liquid crystal (LC) in tunable microwave devices. For this purpose, a line based passive phase shifter is designed and implemented in a ridge gap waveguide (RGW) topology and filled with LC serving as functional material. The inherent direct current (DC) decoupling property of gap waveguides is used to utilize the waveguide surroundings as biasing electrodes for tuning the LC. The bed of nails structure of the RGW exhibits an E-field suppression of 76 dB in simulation, forming a completely shielded device. The phase shifter shows a maximum figure of merit (FoM) of 70 °/dB from 20 GHz to 30 GHz with a differential phase shift of 387° at 25 GHz. The insertion loss ranges from 3.5 dB to 5.5 dB depending on the applied biasing voltage of 0 V to 60 V.

This paper presents an overview of fully dielectric antenna arrays with integrated dielectric power dividers developed at Technische Universität Darmstadt as an extension of previous work. The power dividers are based on the principle of multimode interference and offer one- and two dimensional power division in a single step,which allows the realization of small and lightweight devices. In order to prove the concept, 1 ×4 and 4× 4 fully dielectric antenna arrays with integrated power dividers milled from Rexolite are designed, realized and characterized, operating between 90 GHz and 105 GHz. To assess miniaturization and beamsteering capabilities, three 1 × 4 arrays composed of different materials, Rexolite, Preperm L300 and Preperm L440, are compared regarding gain, size,weight and element spacing. Depending on array size and material, gain is between 12.5 dBi and 22 dBi, accompanied with sidelobe levels below –7.5. All demonstrators are realized by milling, but the designs show the potential to be 3D printed or injection molded for large scale manufacturing.

A passive wireless temperature sensor with identification capabilities based on a phase modulation scheme is discussed in this paper. The approach presented utilizes a pulse backscatter technique based on slow wave (metamaterial) transmission lines. The focus of the work are the material engineering for the temperature-sensitive element and the integration of this element into a passive phase modulation circuit and the entire sensor tag. The approach makes use of temperature-sensitive bariumstrontium-titanate thick film capacitances. The discussed principle has been experimentally verified with a prototype.

The paper is focused on the influence of the morphology of barium strontium titanate (BST) thick-films on their effective dielectric properties. Therefore two BST thick-films are made with a minor deviation in sinter temperature, and hence their mean grain size of the films and their sintering necks. By modeling the meso-structure using a Nonlinear 3D Finite-Difference Time-Domain field solver the assumed effect of the morphology on the effective dielectric properties are confirmed. The simulation results show the potential for a further improvement of the dielectric tunability of BST thick-films.

In this paper we present the impact of acoustic resonances excited by electrostriction in BST thin-films on the Q-factor of a varactor in the GHz range. By changing the process-parameter substrate to target distance while sputtering the thin-films, we observe a change in the acoustic resonance frequencies. To characterize the material properties which determine the acoustic resonance frequencies a model based on a 1D acoustic transmission line is used. The extracted material properties results in a proportional dependency to the changed process parameter. For verification of the acoustic transmission line model 3D simulations have been performed which show good agreement to the line model for lower resonance frequencies, where the difference at higher frequencies becomes significant due to additional higher order modes.

Tunable Liquid Crystal (LC)-based microwave components are of increasing interest in academia and industry. Based on these components, numerous applications can be targeted such as tunable microwave filters and beam-steering antenna systems. With the commercialization of first LC-steered antennas for Ku-band e.g., by Kymeta and Alcan Systems, LC-based microwave components left early research stages behind. With the introduction of terrestrial 5G communications systems, moving to millimeter-wave communication, these systems can benefit from the unique properties of LC in terms of material quality. In this paper, we show recent developments in millimeter wave phase shifters for antenna arrays. The limits of classical high-performance metallic rectangular waveguides are clearly identified. A new implementation with dielectric waveguides is presented and compared to classic approaches.

A passive wireless temperature sensor with identification capabilities based on a phase modulation scheme is discussed in this paper. The approach presented utilizes a pulse backscatter technique based on slow wave (metamaterial) transmission lines. The focus of the work are the material engineering for the temperature-sensitive element and the integration of this element into a passive phase modulation circuit and the entire sensor tag. The approach makes use of temperature-sensitive bariumstrontium-titanate thick film capacitances. The discussed principle has been experimentally verified with a prototype.

For the realization of tunable matching networks, different approaches based on functional materials or micromechanical devices with varying performances has been presented in the past. The dynamic control of these devices requires the measurement of the transmitted power. This paper evaluates different methods for adequate power measurement within the context of mobile communication devices in the frequency range of 500 MHz to 5 GHz. The circuits are analyzed and compared concerning their insertion loss, integrability, size and multiband-capability.

The paper is focused on the influence of the morphology of barium strontium titanate (BST) thick-films on their effective dielectric properties. Therefore two BST thick-films are made with a minor deviation in sinter temperature, and hence their mean grain size of the films and their sintering necks. By modeling the meso-structure using a Nonlinear 3D Finite-Difference Time-Domain field solver the assumed effect of the morphology on the effective dielectric properties are confirmed. The simulation results show the potential for a further improvement of the dielectric tunability of BST thick-films.

In this paper we present the impact of acoustic resonances excited by electrostriction in BST thin-films on the Q-factor of a varactor in the GHz range. By changing the process-parameter substrate to target distance while sputtering the thin-films, we observe a change in the acoustic resonance frequencies. To characterize the material properties which determine the acoustic resonance frequencies a model based on a 1D acoustic transmission line is used. The extracted material properties results in a proportional dependency to the changed process parameter. For verification of the acoustic transmission line model 3D simulations have been performed which show good agreement to the line model for lower resonance frequencies, where the difference at higher frequencies becomes significant due to additional higher order modes.