Saygin Bildik

Reconfigurable Folded Reflectarray Antenna Based Upon Liquid Crystal Technology

A reconfigurable antenna based on the liquid crystal technology is presented in this paper. The antenna comprises a planar lower reflector with an incorporated feed at its center and a polarizing grid on top as an upper reflector. The lower reflector is utilized to collimate the beam and to twist the polarization. The polarizing grid selects the polarization for the transmission and reflects the orthogonally polarized waves toward the lower reflector. Combining reflector elements with a polarizing grid allows performing additional phase adjustment on the upper reflector for beam steering. Reconfigurability is maintained by the upper reflector, in which a liquid crystal mixture is used as a tunable substrate. The liquid crystal layer is tuned with a bias voltage configuration to obtain an appropriate phase adjustment for the beam steering. As a proof of concept, the beam steering capability of the antenna is demonstrated by steering the main beam to -6°, 0 °, and 6 ° at 78 GHz. The measured gain at 78 GHz is 25.1 dB. The proposed antenna configuration is a promising candidate for reconfigurable, high-gain, low-profile, and low-cost antennas.

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.

Compact tunable Ka-band phase shifter based on liquid crystals

This paper presents the design and realization of a compact phase shifter based on a tunable dual-mode ring filter at 35 GHz. The tunability is achieved by employing a thin liquid crystal layer as a tunable dielectric substrate. By applying a bias voltage in the range of 0… 40V, a tunable phase range of 117° is measured. The figure of merit of the realized phase shifter is 30.6 °/dB at 34.3 GHz.

Ka-band frequency tunable patch antenna

In this paper we present a frequency tunable patch antenna working in the Ka-band. Liquid Crystals are used as a tunable dielectric layer between a ground plane and an inset feed microstrip patch. Measurements show, that the resonance frequency of the antenna can be tuned continuously from 34.1 GHz to 37.7 GHz with bias voltages between 0 and 90 V.

Temperature investigations of liquid crystal based reconfigurable reflectarrays

The effects of temperature variations on liquid crystal based reconfigurable reflectarrays are investigated. A Ka-band reconfigurable reflectarray that is made of microstrip patch elements has been used for this purpose. Measured far-field patterns and gain of the reflectarray antenna are presented at different temperatures at 36 GHz. Beam steering time measurements are also carried out at different temperatures, i.e., between 15 °C and 35 °C, for the 0° to -20° beam steering case.

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 °.