R. Marin

Basic investigations of 35 GHz reflectarrays and tunable unit-cells for beam steering applications

Three realisations of 35 GHz reflect arrays with fixed beam are presented. The first single-layered reflect array uses variable patches as phase-shifting element and serves as reference. The second one, employing patches of variable size loaded with variable length slots in the ground plane, and the third one, a double-layered reflect array using stacked patches of variable size, are designed to achieve higher bandwidth. In the second part of the paper a novel concept for a tunable reflect array unit cell using liquid crystals is presented and verified. Measurements performed in a waveguide simulator were able to demonstrate 300/spl deg/ phase tunability of a unit cell, by applying voltages up to 40 V.

Investigations on 77 GHz tunable reflectarray unit cells with liquid crystal

This paper presents investigations conducted with tunable reflectarray unit cells based on nematic liquid crystals (LC), at frequencies around 77 GHz. The structure of the cells is presented, as well as their performance as measured in a waveguide simulator setup. Encouraging results with tunable phase ranges as high as 280° with tuning voltages of up to 15V have been achieved. The investigated tunable unit cells will be used in electronically reconfigurable reflectarrays.

Realization of 35 GHz Steerable Reflectarray using Highly Anisotropic Liquid Crystal

This paper investigates the realization of reconfigurable reflectarrays based on tunable liquid crystals (LC). Two different concepts of unit cells using highly anisotropic LC have been designed and measured, showing good results and the possibility of employing them in a full-scale reflectarray. A 16 times 16 fixed beam microstrip reflectarray has been developed and measured, in order to verify the feeding concept. Good agreement is obtained between simulation and measurement

Liquid Crystals — Microwave Characterization and Tunable Devices

Liquid crystals (LCs) in the nematic mesophase are investigated in the microwave region. A characterization method based on a rectangular waveguide resonator is shown, which is able to extract the anisotropy of LCs. Various LCs are measured their properties at 30GHz is presented. They can be used in microwave devices to change the effective permittivity and therefore tuning the device properties. A broadband phase shifter device between 1.125GHz and 35GHz and a reflectarray operating at 35GHz is discussed. Additionally, the measurement results of unit-cells of reflectarrays at 77GHz are also presented, encouraging a realization of reflectarrays at W-Band. Index Terms – Liquid crystal, tunable device, phase shifter, reflectarray, Microwave device, Reconfigurable devices

Electronically Reconfigurable LC-Reflectarray with 2D Scanning Capability and SU-8 structured Cavity

The realization and characterization of an electronically reconfigurable reflectarray based on liquid crystals is presented, which is able to steer the main beam continuously in between 358 ba using the LC MDA-03-2844. It features 2D-reconfigruration capability and the structuring of the LC cavity with SU-8 photo resist. Index Terms – Liquid Crystal, Reflectarray, tunable Reflectarray, SU-8

Compact Cross-Coupled Microstrip Bandpass Filter with Improved Stop-Band Characteristics

Abstract This paper presents the design of a filter configuration, combining hairpin and open-loop resonators to achieve compact size, maintaining low insertion loss and high selectivity. Two filters were fabricated for a 1.75 GHz center frequency: a four pole filter with open-loop resonators and its counterpart using two hairpin and two open-loop resonators. Simulations and measurements of the two realized filters are presented with the purpose of comparing their responses.