Christian Schuster

Tunable dielectric delay line phase shifter based on liquid crystal technology for a SPDT in a radiometer calibration scheme at 100 GHz

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.

Dual Frequency Selective Multiple Access With Quasi-Chipless/Powerless RFID Mixer Tags

A novel concept of quasi-chipless RFID Mixer tags is introduced in this letter, that extends the harmonic radar principle by a multiple access scheme. In this scheme, two RF signals being transmitted by a reader are downconverted in the tag by an unbiased diode mixer after reception only when the interrogation frequencies of both signals do match the filter characteristics of the two narrow-band receiving antennas. Only in this case, the downconverted RF signal is backscattered toward the reader by a third narrow-band antenna. Thus, several tags can be addressed by individual frequency pairs, what allows for the implementation of a multiple access scheme. This scheme is discussed in detail and accompanied by a proof-of-concept implementation. The functionality has been verified by corresponding measurements of different tag combinations and a read range analysis has been performed.

Tunable microwave component technologies for SatCom-platforms

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. Special attention is given to tunable components based on functional materials such as barium strontium titanate (BST) and liquid crystal (LC).

Concept and design of a 40 GHz differential sensor for the analysis of biomedical substances

This paper discusses a low cost coplanar differential sensor at 40 GHz suitable for the lab on chip integration. Its ability to resolve small permittivity differences with a high dynamic range was proved by analytical calculations and full-wave EM simulations and was finally validated with measurements. A sensitivity of τ = 2.5dB/%Δεr>eff was achieved for small permittivity differences. Thereby, a change of 100 % ethanol to 99 % ethanol mixed with 1 % DI water, results in a difference of ΔS21 = 5 dB. In order to further minimize the complexity e.g. for single use purposes, the influence of the absence of the termination resistors of the couplers was investigated.

Performance Analysis of Reconfigurable Bandpass Filters With Continuously Tunable Center Frequency and Bandwidth

This paper presents a comparison and performance evaluation of three different technologies for the implementation of tunable filters utilizing semiconductor varactors, commercially available barium strontium titanate (BST) thin film and screen-printed BST thick-film varactors. To identify the most suitable technology for applications in low power receiving up to high-power transmitting stages, the performance evaluation is carried out with the same tunable hairpin filter design. While the center frequency of the proposed tunable filter structure is tuned by varactors loading the filter resonators, the bandwidth is controlled by coupling varactors between adjacent resonators. The filters are designed for a center frequency range from 700 MHz to 1 GHz and for bandwidth tuning from 60 to 150 MHz. The tunable filters are evaluated and compared with regard to their tunability, quality factor, linearity (intermodulation products of third order), and power handling capability. In conclusion, the tunable hairpin filter based on semiconductor varactor diodes offers the largest center frequency tuning range of 390 MHz with a transmission between −1.5 and −7 dB, whereas the BST thin- and thick-film-varactors-based filters exhibit high linearity with an IIP3 between 39 and 60 dBm. Moreover, large signal characterization reveals that the BST thick-film-varactors-based filter structure has the best power handling capability of up to 41dBm.

Tunable lumped-element-filter for RF power applications based on printed ferroelectrics

This work addresses center frequency and bandwidth tunable filter for implementation in RF base-station front-ends. The filter is fabricated using functional thick-film layers of Barium-Strontium-Titanate (BST). The deposition of BST layers is performed locally in a screen printing process. The fabricated varactors have a Q-factor around 40 at 1 GHz, a tunability larger than 50% and a measured IP3 higher than 65 dBm. The filter is designed to cover typical GSM frequencies from 700 MHz to 960 MHz and 60 MHz to 100 MHz bandwidth. The simulated insertion loss is around 2.2 dB and 3.0 dB, depending on the center frequency and bandwidth. Measurements of the filter reveal an insertion loss of 6 dB to 9 dB which is at least 4 dB higher than predicted by simulations.

Unobtrusive Recognition of Working Situations

In many countries, people are obliged to remain in their jobs for a long time. This results in an increased number of elderly people with certain disabilities in working life. Therefore, a support with technical assistance systems can avoid further health risks and help employees in their everyday life. An important step for offering a suitable assistance is the automatic recognition of working situations. In this paper we explore the unobtrusive data acquisition and classification of working situations above a tabletop surface. Therefore, a grid of capacitive sensors is deployed directly underneath the tabletop.