Martin Schubler

Artificial Line Phase Shifter with separately tunable Phase and Line Impedance

Based on the theory of metamaterial transmission lines, a phase shifter with independently controllable phase shift and line impedance is developed. The possibility of separate Deltaphi and Z L tuning reduces mismatch losses and leads to an increased performance, or can be applied for a combined phase shifter attenuator circuit. The presented phase shifter operates at a frequency of 6.5GHz with a FoM of 60 to 70deg/dB over a 30% bandwidth region. The second operation mode shows a 0deg-90deg differential phase shift with 0dB-10dB differential magnitude control with 10% bandwidth around 5GHz

Microwave mass flow sensor for process monitoring applications

A particulates mass flow meter has been developed using a cylindrical waveguide resonator. Two directional MicroStrip-Patch couplers confine the resonant measurement section of the sensor without any disturbance of the material flow in the pipeline. A new extraction algorithm has been introduced to detect the material concentration and the velocity of particulate solids out of a single time continuous measurement. The autocorrelation function and the pre-knowledge of the time dependent phase shift, when particles flying through the sensor, where used for precise particle velocimetry. Measurements with a built up sensor at 5.5 GHz where carried out to prove the concept. Application areas of this sensor type are gas/solids, gas/liquid and low loss liquid/solid flows in various industrial applications.

Thermal Coupling in Multi-finger Heterojunction Bipolar Devices

IThe thermal characteristics of power HBT devices are considered. The analysis includes emitter finger coupling and limitation in power operation due to selfheating. An essential part of the generated heat is dissipated through the top device layers and metal contacts. A strongly uneven temperature distribution in the emitter finger of multi-finger devices is the result of not sufficient temperature drain through the emitter air-bridge. Sufficient thermal dissipation can be additionally obtained by temperature drain through the base and collector metallised areas on top of the device. An optimum distance between individual emitter fingers exists for maximum thermal coupling. This yields better thermal homogeneity.

Filter-based slow wave structures for application in chipless microwave RFID

A new concept for implementing delay elements in chipless TDR RFID tags is presented. It is based on filter design techniques and aims for less dispersive and compact designs. Since dispersion has influence on ISI and phase distortion, a reduction of the dispersion leads to an increase in the systems performance and the read range, respectively. This is first analyzed with the help of a system-theoretic simulation. From the filter design methods considered in this paper, the Butterworth method shows to be best suited for this purpose. An adaption of the Butterworth filter design regarding group delay design requirements is derived. A filter design is carried out and a delay section with low group delay dispersion is implemented. Finally, a prototype tag is realized and measured to verify the applicability of the designed filter-based slow wave structure for chipless TDR RFID tags.

Design and realization of a microwave applicator for diagnosis and thermal ablation treatment of cancerous tissue

Microwave sensors play a significant role in medical environments. The contact-less and non-invasive sensing mechanism to determine the dielectric properties of tissue is of great advantage. In this work, a dual mode microwave sensor is designed to combine the diagnosis and treatment of cancer in one minimal invasive surgery tool. In order to detect abnormalities, the relative change of permittivity of healthy tissue compared to tumor tissue is evaluated. For the treatment mode, microwave ablation is used to eradicate malignant cells. The challenges of the design process are the dimension limitation and packaging with an appropriate interface of the sensor integrated in a needle-like surgery tool. The small size leads to a significant increase of the operating frequency up to 40GHz with the advantage of using very low input power for the thermal ablation procedure. The sensor provides a maximum temperature of over 100°C with 2W input power. Prototypes of the proposed sensors are fabricated to measure the transmission characteristics of the structures unloaded and loaded.

Neural networks for microwave characterization of material samples in rectangular cavities

In order to characterize material samples of different sizes at microwaves, use was made of a rectangular metallic cavity, which is partially filled by these material samples, having arbitrary locations. Subsequently, by using a multi-layer perceptron (MLP) network, its dielectric constant, dielectric losses and its amount could be accurately extracted from measurements of the magnitude of the scattering parameter |S/sub 11/| only, since the phase information was not available. The input for this network is generated by a proper preprocessing of the simulated and measured magnitude of the return loss |S/sub 11/|. The investigations indicate very good agreement of the simulated and measured data, thus, a simulation-based training of neural networks and an subsequent parameter extraction of the material samples from |S/sub 11/|-measurements was possible with high accuracy.

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.