Sebastian Strunck

Continuously Polarization Agile Antenna by Using Liquid Crystal-Based Tunable Variable Delay Lines

In this paper, a polarization agile planar antenna is presented by using tunable liquid crystal (LC) material. The antenna includes a 2 × 2 dual-fed microstrip patch array and two separate feeding networks for each feeding of the dual-fed antenna. The polarization state of the antenna can be controlled continuously between dual linear and dual circular polarizations depending on a differential phase shift between the antenna feedings. The feeding networks are implemented in inverted microstrip line topology with the liquid crystal material as a tunable dielectric. A desired differential phase shift is obtained between the feeding networks by tuning the LC material. Thus, no additional tunable components are required according to proposed antenna topology. Additionally, owing to the continuous tuning of the LC material, any polarization state between the circular and linear ones are achievable. The antenna prototype is designed at 13.75 GHz. The measured return losses are greater than 10 dB in a frequency range of 13.5 to 15 GHz for different polarization states. Far-field pattern measurements are performed, which confirm the continuous tuning of the antenna polarization. Specifically, the measured antenna patterns are presented for ±45° linear and right-handed circular polarizations. The prototype can be fabricated in a larger size with more radiating elements and can be efficiently scaled for higher operating frequencies at the Ka-or W-band since the LC material features even lower dielectric losses at higher frequencies.

A 2-D Electronically Steered Phased-Array Antenna With 2

For the first time, a 2-D electronically steered phased-array antenna with a liquid-crystal (LC)-based variable delay line is presented. The structure, which is designed at 17.5 GHz, consists of a 2 × 2 microstrip patch antenna array, continuously variable delay lines with a novel geometry, RF feeding, and biasing networks. The expected insertion loss of the variable delay line is less than 4 dB with a maximum differential phase shift of 300°. During the measurements, the antenna is steered by applying an appropriate dc biasing in the range of 0-15 V to the variable delay lines. It is also shown that the return loss is always better than 15 dB at the operating frequency when the antenna is steered.

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This paper presents a novel liquid crystal technology for tunable microwave devices, primarily developed by the TU Darmstadt and Merck consortium over the last 10 years. This paper focuses on quasi powerless continuous (analog) tuning of phase shifters implemented in different transmission line topologies, which are used for electronically-controlled phased arrays aimed for various applications and frequency ranges. It consists of phase shifters and antenna arrays in planar topologies, in LTCC microstrip line and substrate integrated waveguide and rectangular waveguide topologies using liquid crystal filled cavities to tune the velocity of the traveling waves along the various line phase shifters. The measured figure of merit of the various phase shifter values range from 45° dB-1 to 72° dB-1 @ 30 GHz for LTCC integrated phase shifters and 62.5°dB-1 @ 17.5 GHz for planar phase shifters as well as 120° dB-1 to 200° dB-1 for waveguide phase shifters. Besides the phase shifter performances, far field measurements are presented as well to demonstrate the scanning capabilities of a 2 × 2 and 4 × 1 array antenna built with different topologies.

2 Elements in LC Display Technology

A tunable substrate-integrated waveguide phase shifter using low-temperature co-fired ceramic (LTCC)-technology is presented in this paper. By changing the effective permittivity in the liquid crystal (LC)-filled waveguide, the differential phase can be tuned continuously. This is achieved by means of an analog signal applied to the electrodes, surrounding the LC. The design allows for precise tuning of the differential phase, which is proven with a Monte Carlo measurement resulting in phase errors of less than 3° at 28 GHz. Besides that, the ambient temperature dependency of the module is shown. The phase shifter has a high integration level and can be included into a complete and lightweight single-phased array antenna module. The phase shifter is realized with a high level of integration which is available through the multilayer process of the LTCC. It has a length of 50 and provides a differential phase shift of more than 360° at 28 GHz. The figure of merit for tunable phase shifters is >40°/dB.

Continuously tunable phase shifters for phased arrays based on liquid crystal technology

This paper presents the design and realization of a tunable periodically loaded slot line phase shifters. The tunability is achieved by using liquid crystal (LC) as a tunable dielectric. Two prototypes are fabricated based on a printed circuit board (PCB) - LC - PCB structure for 12 GHz and a glass - LC - glass structure for 18 GHz. Measurements are performed and the figure of merits of the phase shifters are determined as 47 °/dB and 42 °/dB, respectively.

Reliability study of a tunable Ka-band SIW-phase shifter based on liquid crystal in LTCC-technology

Low Temperature Cofired Ceramic (LTCC) is used as a substrate material for microelectronic devices in satellite communication. Its dielectric properties and excellent variability allows a good compactness and a high level of integration. An LTCC antenna array for microwave signals operating at 30 GHz is presented. All components such as radio frequency distribution network, four waveguide phase shifters and horn antennas are integrated in one ceramic module. The phase shifters are implemented as high volume cavities in the LTCC. A tailored mixture of liquid crystal can be stored inside the cavities. By applying an electric field, the anisotropic LC-molecules are aligned. The field is provided through a biasing network with four electrodes and screen printed resistive layers with resistance values in the MΩ/□ range. The alignment and with it the phase shifting is nearly seamless. The antenna module is manufactured in multilayer technology and consists of more than 40 layers. Lamination is carried out by th...