This letter presents a steerable phased-array antenna at C/X-band. The phase shifters used in the design, are implementing inkjet-printed barium strontium titanate (BST) thick-films. This method ...enables low-voltage tuning and low fabrication cost. The phase shifter is tuned by integrated metal-insulator-metal varactors, whose electrodes are fabricated by photolithography and inkjet-printed dielectric layer. A tunability of 46% at 8 GHz is achieved by applying 50 V across a 1.2- μm-thick BST film. The 11-unit-cells loaded-line tunable phase shifter achieves a figure of merit above 40°/dB from 7 to 8.5 GHz. Dielectric resonator antenna, fabricated from bulk-glass ceramic, has been implemented as radiating element with a stacked architecture for wide bandwidth and high gain. A beam steering of ±30° has been measured with a 1 ×4-element phased array in the anechoic chamber.
In the field of oxide electronics, there has been tremendous progress in the recent years in atomic engineering of functional oxide thin films with controlled interfaces at the unit cell level. ...However, some relevant devices such as tunable ferroelectric microwave capacitors (varactors) based on BaxSr1−xTiO3 are stymied by the absence of suited compatible, very low resistive oxide electrode materials on the micrometer scale. Therefore, we start with the epitaxial growth of the exceptionally highly conducting isostructural perovskite SrMoO3 having a higher room-temperature conductivity than Pt. In high-frequency applications such as tunable filters and antennas, the desired electrode thickness is determined by the electromagnetic skin depth, which is of the order of several micrometers in the frequency range of a few gigahertz. Here, we report the pulsed laser deposition of a fully layer-by-layer grown epitaxial device stack, combining a several micrometers thick electrode of SrMoO3 with atomically engineered sharp interfaces to the substrate and to the subsequently grown functional dielectric layer. The difficult to achieve epitaxial thick film growth makes use of the extraordinary ability of perovskites to accommodate strain well beyond the critical thickness limit by adjusting their lattice constant with small shifts in the cation ratio, tuned by deposition parameters. We show that our approach, encompassing several orders of magnitude in film thickness scale whilst maintaining atomic layer control, enables the fabrication of metal-insulator-metal (MIM) varactors based on 50–100 nm thin BaxSr1−xTiO3 layers with high tunability above three at the Li-ion battery voltage level (3.7 V).
A novel package integrated solution for gallium nitride high-electron-mobility transistors with an electronically two-dimensional reconfigurable L-section matching network is presented. Thick-film ...barium-strontium-titanate (BST) varactors are used to realise a tunability of the load impedance of 1:2 in resistive and 1:1.5 in reactive parts, respectively, applying tuning voltages of up to 200 V. The tuneable module achieves a peak output power of 43.2 dBm (20.9 W). Comparison with simulated results using field simulations and a large-signal model shows good agreement in terms of output power and power added efficiency and thus proves the concept of using metal–insulator–metal BST varactors for reconfigurability.
This paper presents for the first time, an electrically tunable dielectric line based on fiber topology. A fiber segment is filled with liquid crystal (LC) for continuous tuning of the differential ...phase between 0° to 90° by an applied biasing voltage of up to ±500 V. This phase shifter is aimed to be implemented into a RF switch (Single-Pole Double-Throw, SPDT), to switch between the calibration loads and the antenna of a radiometer at 100 GHz. A subwavelength topology was chosen, where compared to classical dielectric waveguides, air is acting as cladding material, ensuring a low loss propagation comparable to hollow waveguides. The phase shifting section has a total length of 26mm and provides a maximum differential phase shift of more than 107° and 115° at 100GHz for electric and magnetic biasing, respectively. Accompanied by insertion losses between 2.5 dB to 3.0 dB, the phase shifter shows a figure of merit at 100GHz of 42 °/dB for electric and 44 °/dB for magnetic biasing.
A tunable frequency selective surface (FSS) with beam steering capability is presented. The FSS is used as a transmitarray with a bandpass characteristic in Ku-band. The periodic sub-wavelength (λ 0 .../25) unit-cells are composed of capacitive and inductive structures creating a bandpass for an incident wave. By patterning the capacitive elements on a screen-printed barium-strontium-titanate (BST) thick-film ceramic, the resonant frequency of the FSS can be tuned. This technology offers a simple and cost effective way for integrating varactors into the FSS and is particularly attractive for microwave circuits with a high varactor density. A prototype is fabricated including two capacitive layers with an overall size of 40 mm × 40 mm. Each layer includes a total of 1600 integrated BST varactors that are fabricated by using a patterning and metallization process. A transmitted wave passing through the FSS will experience a phase shift, which can be tuned by tuning the passband. This allows steering the transmitted wave to a certain direction by applying a phase gradient along the FSS interface. A phase shift range of 360° can be covered by cascading several FSS panels. The prototyped tunable FSS demonstrates the feasibility of the proposed technology and its potential for beam steering.
As the ionic conductivity of solid-state lithium ion conductors rises, knowledge of the detailed conductivity mechanisms is harder to obtain due to the limited frequency resolution of the traditional ...impedance spectrometers. Moreover, the data is easily affected by the local microstructure (i.e. pores, grain-boundaries) and the preparation conditions. The aim of this work is to demonstrate the feasibility of the coaxial reflection technique as a reliable tool to study fast ionic conductors (i.e. > 10−4 S cm−1). Especially the relative permittivity can be determined more accurately at room temperature. For the first time the electrical performance of LATP and LLZO manufactured via a scalable top-down glass-ceramic route is evaluated. The density turns out to be a key parameter influencing both relative permittivity and resulting conductivities. For a 100% dense LATP sample the coaxial reflection technique reveals a high grain-core conductivity of 6 × 10−3 S cm−1 similar to the conductivity of ideal single crystals.
A low-cost phased-array antenna at 10 GHz is presented for a scan angle of ±50°. The array employs continuously tunable phase shifters based on a screen printed barium-strontium-titanate thick-film ...ceramic. Due to the use of artificial transmission line topology, the proposed phase-shifter design has a very compact size (3 mm × 2.8 mm) for 342° total phase shift. In the frequency range from 8 to 10 GHz, it exhibits a figure of merit >;52°/dB, which is among the best of phase shifters based on ferroelectric thick films. In a prototyped phased array, the RF circuit consists of a feeding network, phase shifters, and antenna elements, which are integrated into one planar metallization layer. Furthermore, a simple way for routing bias lines for phase shifters is demonstrated using high resistive electrodes. Using screen printed thick films and applying a simplified fabrication process for the RF and bias circuitry can reduce the total expense of phased arrays considerably.
The composite system Ba0.6Sr0.4TiO3/Mg3B2O6 (BST/MBO) was investigated in regard to the influence of sintering temperature and composition on the dielectric properties. Dilatometry measurements were ...carried out at up to 1200 °C. At 1050 °C, all composites with an MBO content of 22.0 vol% or more showed densities over 90 % of the theoretical value. An in-situ XRD study was conducted at up to 1200 °C. The formation of Mg2TiO4 was detected starting at 1120 °C. These data sets were used to make a set of compositions ranging from 17.8–79.7 vol% MBO. At 1050 °C, the element distribution at the BST/MBO interfaces was investigated via EDX and ToF-SIMS. It was observed that titanium migrates from the BST into the MBO, mostly in the interface region. The microstructure of the different compositions was determined via SEM and image analysis. Traces of a third phase were found even for samples sintered at 1050 °C. The dielectric properties of the samples were measured at 13.56 MHz and compared to the expected behavior from the literature. It was found that compositions in the middle of the spectrum showed reduced permittivity, loss, and tunability, resulting in an overall increase in the material quality factor when compared to the chosen model. This was attributed to the passivation of the BST at the interfaces.
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