Andre Giere

Modeling and Applications of Ferroelectric-Thick Film Devices With Resistive Electrodes for Linearity Improvement and Tuning-Voltage Reduction

Low-cost planar high-Q ferroelectric-thick film varactors (Qap90) are realized and component architectures using resistive electrodes for dc bias are investigated. A basic model for planar capacitors with resistive electrodes in the gap is developed and verified by finite-difference time-domain simulations and measurements of interdigital capacitors with high-resistivity indium-tin-oxide bias electrodes in the gap. An optimized high-Q capacitor design based on a series connection of ferroelectric varactors with resistive bias decoupling is presented. The approach allows the increase of device linearity and the reduction of tuning voltages. Based on this technology, a continuously tunable high-power impedance-matching network for 1.875 GHz with tuning voltages below 60 V was developed, realized, and characterized by small- and large-signal measurements with up to 33-dBm input power. The device requires no external dc-block or RF decoupling and features separated RF and dc contacts. The output IP3 of up to 47.8 dBm verifies the excellent device linearity

Phase modulation scheme for chipless RFID- and wireless sensor tags

Inspired by state of the art surface acoustic wave (SAW) technique an approach for the realization of chipless microwave RFID tags based on electrical circuits is proposed. For information coding of the retransmitted signal a passive QPSK coding scheme and for wireless monitoring of physical quantities an analog phase modulation scheme are investigated. Key elements for the realization of tags are lumped element delay lines. Therefore properties of left- and right-handed lines are discussed with the view on the special application. Finally, the proposed principles have been experimentally verified with a prototype.

LH phase shifter using ferroelectric varactors

A tunable left handed (LH) transmission line used as continuously tunable phase shifter is presented. Using varactors based on barium-strontium-titanate (BST) thick films, a figure of merit FoM = 29deg /dB has been measured at 2.8 GHz. The bandwidth of the realized circuit using 3 unit cells reached 10%. The agreement of the presented result from simulation and measurement is good, the differences can be explained by tolerances of the used components. Additionally the simulations of a 180deg phase shifter based on the same components for the unit cell is presented. Simulated results of this phase shifter shows a bandwidth of 27% and a FoMmax = 31.5deg /dB

Suppression of harmonic radiation of tunable Planar Inverted-F Antenna by ferroelectric varactor loading

Low-cost ferroelectric varactors based on Barium-Strontium-Titanate (BST) thick-film technology have been implemented in a tunable Planar Inverted-F Antenna (PIFA). A prototype is realized and measured. The harmonic radiation is evaluated in detail. It is shown that, considerable RF voltage detunes the varactor and stimulates harmonic radiation in the varactor-loaded PIFA. It is discussed how such radiation can be suppressed by choosing the varactor’s tuning behavior. The passive BST thick-film varactors are proven to have advantages in reducing the harmonic excitation. When compared to a reference design using a silicon diode, the prototype shows suppressions on the second harmonic radiation up to 35.7 dB at −10 dBm input power. Possible suppression by BST thin-film varactors which are featured of low tuning voltages is also discussed.

Influence of Fe–F-co-doping on the dielectric properties of Ba0.6Sr0.4TiO3 thick-films

Abstract The influence of Fe acceptor and Fe – F acceptor – donor co-doping on the dielectric response of screen-printed Ba0.6 Sr0.4 TiO3 thick-films on alumina substrates has been investigated. The Ba0.6 Sr0.4 TiO3 powders were synthesized by freeze-drying of sols. Permittivity, dielectric loss, and tunability were investigated at kHz frequencies with a planar metal-insulator-metal capacitor structure, and at GHz frequencies up to 40 GHz using coplanar waveguide structures. Pure acceptor doping by Fe was found to have a distinct influence on permittivity and dielectric loss-factor at kHz-frequencies and at GHz frequencies due to an internal bias field and pairs of associated defects. Co-doping with F significantly suppresses the influence of the internal bias field and defect-associates at low and microwave frequencies. The commutation quality factor at 10 GHz and Eeff = 5.8 V μm-1 was increased by co-doping the thick-films with Fe and F. Such doped Ba0.6 Sr0.4 TiO3 films show a high potential for tunable microwave applications.

Optimization of uniplanar multilayer structures using nonlinear tunable dielectrics

For an optimization of the tunability of coplanar waveguides (CPW) different geometries have been studied on barium-strontium-titanate (BST) thick films. The presented measurement results show a strong dependency of tunability vs. geometry which can not be calculated using standard conformal mapping (CM) approaches. To calculate a cross section of a CPW, an FDTD (finite difference time domain) algorithm, expanded to field strength dependent relative permittivities has been implemented. A geometry efficiency factor /spl chi/ is introduced to review the effective tunability for different geometries.

Barium strontium titanate thick-films: dependency between dielectric performance and their morphology

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.

Helicopter Near-Field Obstacle Warning System Based on Low-Cost Millimeter-Wave Radar Technology

This paper describes the specific development of a planar and especially low-cost near-field obstacle warning sensor system for helicopters based on an adapted electronically steerable automotive radar. All system components, from the antenna arrays, the RF modules, to the baseband processing, the signal processing algorithms, and 3-D data visualization were developed and a complete system prototype was built. Ground-based system field trials (static and dynamic sensor tests) were successfully performed during which typical obstacles like overhead power lines, trees, and poles were detected and visualized. In addition, algorithms for geo-referencing of the sensor movements and the detected obstacles were developed and verified.

Tunable dielectrics for microwave applications

This paper gives a short introduction into tunable dielectrics for microwave applications based on nematic liquid crystal and Barium-Strontium-Titanate (BST) thin- and thick-films. Due to their tuning voltage dependent electromagnetic properties, both are very promising material candidates for tunable passives in the microwave and millimeter-wave regions. For applications, such as frequency-agile communications and sensor systems we illustrate the challenges of optimization BST films based on a multi-scale view for material, processing, device and application design.

A compact antenna with two independently tunable frequency bands

The proposed novel compact antenna uses two varactor loaded monopole slots to cover simultaneously two wide frequency ranges, while the tuning of each bands are independent. The instantaneous bandwidth and footprint enable an easy integration.