Roland Reese

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.

Comparison of hollow waveguide and dielectric fibre based SPDT switches for W-band

This work presents as a first approach, the comparison of two non-tuneable/switchable W-band single pole double throws (SPDTs), one realised in hollow waveguide and one in subwavelength dielectric fibre technology. For pre-investigations, both SPDTs are equipped with non-tuneable phase shifters, providing a fixed differential phase shift of 90° between the two paths. The waveguide SPDT shows a reflection better than -10 dB and an isolation between the two output ports of around 16 dB. The fibre SPDT shows reflections better than -10 dB over a wide frequency range and down to -25 dB at 100 GHz, but an isolation between 4 dB to 10 dB only. This deviation compared to simulations is due to the sensitivity of the system in terms of fabrication tolerances whereby the needed differential phase shift of 90° has been exceeded. Next, these phase shifters will be replaced by continuously tuneable phase shifters based on liquid crystal technology. At this point, dielectric fibres are a very promising alternative to hollow waveguides.

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.

Design of a continuously tunable W-band phase shifter in dielectric waveguide topology

This work presents a liquid crystal (LC) based phase shifter in a dielectric waveguide (DW) topology consisting of core and cladding for the W-band. For continuous tunability, a part of the core material is replaced by liquid crystal. Furthermore, suggestions of materials for designing such a DW, i.e. for core and cladding, are given in this paper. In comparison to other topologies, the advantage of this topology is that the necessary electric biasing can be realized easily, by placing electrodes directly on the cladding. With an electric biasing of ±550 V, a maximum differential phase shift of 430°, accompanied with insertion losses between 2.8 to 5.5 dB with standard WR10 connections, could be achieved. The maximum figure of merit is around 100 °/dB at 102 GHz.

In-plane hollow waveguide crossover based on dielectric insets for millimeter-wave applications

This paper presents an in-plane hollow waveguide crossover for W-band frequencies. This kind of crossover can be implemented e.g. into a Butler matrix, to simplify the fabrication process significantly. It is based on a partially dielectric filling of the waveguide, focussing the field in the center. The dielectric is placed in the center of a hollow waveguide crossing and has a star-shape. Inside the dielectric filled region, a higher order mode propagation is possible, which has no significant influence on the overall performance of the crossover. It shows an insertion loss between 0.8 dB to 1.0 dB in the frequency range of 101.5 GHz to 108.0 GHz, while the matching is better than −10 dB and even down to −20 dB between 105 GHz to 108 GHz. The isolated ports show transmission coefficients better than −20 dB over the whole frequency range and even down to −50 dB in the best performing frequency range.

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.

Novel Reflectarray Antenna with Quasi-Dipole Unit Cells

This letter presents a novel reflectarray design based on quasi-dipole unit cells. The substrate of the quasi-dipoles is oriented perpendicular to the array surface, giving the advantage of sufficient large area for phase-shifter circuits behind the antenna element. In order to prove the concept at 10 GHz, unit cells are characterized in a waveguide simulator, and far-field measurements of two 8 × 8-element antenna demonstrators are presented. One demonstrator, pointing in a broadside direction, has shown a half-power beamwidth of 15 ° and a sidelobe level of -12 dB in the E-plane. The other demonstrator is pointing toward 20 ° and has shown a sidelobe level of -7 dB with a half-power beamwidth of 20 °.