Matthias Nickel

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.

Artificial gradient-index lens for Ka-band using a single layer fishnet metamaterial

In this paper, an artificial gradient-index lens based on a single layer fishnet metamaterial is presented. By introducing a variation of the geometric features in the unit cell, a phase variation between -180 and +180 degress can be achieved with only one fishnet layer, i.e. a single substrate. The relation between the geometric dimensions and dispersion properties is presented. Furthermore, the beam-scanning capability of the gradient-index fishnet lens is demonstrated at 27.5 GHz and its performance is evaluated by nearfield measurements making the presented single layer fishnet a good candidate for artificial lenses with low weight and fabrication costs.

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).

Interference based W-band single-pole double-throw with tunable liquid crystal based waveguide phase shifters

This work presents an interference based W-band single-pole double-throw (SPDT) in rectangular waveguide and liquid crystal technology. In radiometers, this kind of SPDT can be used e.g. for switching to the calibration load for power calibration. The SPDT is designed with an E-plane power divider, two different paths for the phase shifting regions, being separated by 30 mm to provide enough space for the used magnets for proof-of-concept, and a coupled line combiner, where the interference is taking place. Rexolite 1422 is serving as liquid crystal cavity. The matching is better than −12 dB between 88 GHz to 110 GHz, except a peak around 102 GHz. The insertion loss is less than 3 dB between 89 GHz to 105 GHz, while exhibiting an isolation of at least 9 dB in this frequency range. From 90 GHz to 100 GHz, isolation is even between 10 dB to 12 dB.

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.

Liquid crystal technology for reconfigurable satcom applications

Modern satellite communication scenarios require a steerable antenna pattern e.g. to continuously align the antenna of a low earth orbit satellite toward a geostationary relay satellite. One promising solution especially in the higher frequency bands starting from Ku-band is based on liquid crystal as functional material. Based on the anisotropy of this material tunable components and systems like phase shifters and array antennas can be built. This paper shows the potential of specially synthesized liquid crystals for the use in phased array antennas for SatCom applications.

Electrical biasing scheme for Liquid-Crystal-based tunable Substrate Integrated Waveguide structures

In this paper, an electrical biasing structure is proposed for a tunable Substrate Integrated Waveguide (SIW) device with Liquid Crystal (LC) as the tuning component. The biasing circuits or electrodes are made of chromium and gold layers. Silicon nitride layer, which has a thickness of 1 μm, is employed to isolate the electrodes against ground. Since voltage as high as ±200V may be applied, high breakdown voltages are required. As a proof of concept, a simple LC-SIW phase shifter based on a tunable delay line is manufactured and sealed with the fabricated biasing structure. Simulation results exhibit a Figure of Merit (FoM) of 89°/dB at 20GHz. The fabricated phase shifter give FoM of 32°/dB with switching time of 5s.

Tuneable hollow waveguide devices for space applications based on liquid crystal

This paper presents an overview in the field of passive, continuously tuneable liquid crystal (LC) devices in hollow waveguide topology. In particular, the designs and measurements of a Ka-band phase shifter as well as a K-band band-pass filter based on an LC filled waveguide resonator are shown. Both demonstrators are designated to be space qualified as their field of application is in satellite communications. While the high performance phase shifter will be integrated in a phased array antenna for beam scanning purposes, the high quality (Q) factor band-pass filter will be used to change the operating frequency and band allocation of a satellite.The key feature of the LC based hollow waveguide phase shifter is its high efhciency, dehned by the maximum differential phase shift divided by the maximum insertion loss in all tuning states, which is measured in the design frequency range of 23 GHz to 27 GHz to more than 130°/dB by means of electric biasing. The key feature of the band-pass hlter is its high Q-factor of up to 484, resulting in a comparatively small bandwidth compared to common hlters based on planar topologies. For the presented hlter, a relative bandwidth of 1% is measured at 20 GHz.