Jose A. Encinar

Dual-Polarization Dual-Coverage Reflectarray for Space Applications

A breadboard of a three-layer printed reflectarray for dual polarization with a different coverage in each polarization has been designed, manufactured, and tested. The reflectarray consists of three layers of rectangular patch arrays separated by a honeycomb and backed by a ground plane. The beam shaping for each polarization is achieved by adjusting the phase of the reflection coefficient at each reflective element independently for each linear polarization. The phase shift for each polarization is controlled by varying either the x or y patch dimensions. The dimensions of the rectangular patches are optimized to achieve the required phase shift for each beam at central and extreme frequencies in the working band. The reflectarray has been designed to produce a contoured beam for a European coverage in H-polarization in a 10% bandwidth, and a pencil beam to illuminate the East Coast in North America in V-polarization. The measured radiation patterns show that gain requirements are practically fulfilled in a 10% bandwidth for both coverages, and the electrical performances of the breadboard are close to those of a classical dual gridded reflector

A Transmit-Receive Reflectarray Antenna for Direct Broadcast Satellite Applications

A 1.2-meter reflectarray antenna has been designed to accomplish the requirements of a Direct Broadcast Satellite (DBS) mission, which provides a South America transmit-receive coverage in Ku band. The antenna has been designed by applying first of all a pattern synthesis technique to obtain the required phase distribution on the reflectarray at several frequencies in transmit and receive bands. Then, the patch dimensions have been optimized in a configuration made of three stacked layers of varying-sized patches in order to provide the required phase distribution at transmit and receive frequencies. An antenna demonstrator has been manufactured and tested. The measured patterns are in good agreement with the simulations and they are close to fulfill the coverage requirements in both transmit and receive bands.

Folded multilayer microstrip reflectarray with shaped pattern

A folded multilayer printed reflectarray with shaped pattern is demonstrated. The configuration consists of a multilayer twister reflectarray, a centered feed embedded in its structure and a polarizing grid, which acts as reflector and radome for each polarization, respectively. A design procedure, valid for obtaining any arbitrary shaped pattern, has been implemented. In order to achieve the pattern specifications along a frequency band, initially a multifrequency pattern synthesis method, which relies on a phase-only synthesis, is applied to obtain the required phase-shift on the reflectarray surface. Afterwards, each stacked patch is individually optimized to generate the required phase-shift previously synthesized. The method has been successfully applied to a LMDS base station antenna, characterized by a sectorial cosecant squared beam in the band 24.5-26.5 GHz. A breadboard consisting of a folded 3-layer circular reflectarray is presented. Measurements show a good concordance with theoretical patterns at 25 GHz, and good shaping of the beam along 24-26 GHz.

Reflectarray Antennas for Dual Polarization and Broadband Telecom Satellite Applications

A reflectarray antenna with improved performance is proposed to operate in dual-polarization and transmit-receive frequencies in Ku-band for broadcast satellite applications. The reflectarray element contains two orthogonal sets of four coplanar parallel dipoles printed on two surfaces, each set combining lateral and broadside coupling. A 40-cm prototype has been designed, manufactured, and tested. The lengths of the coupled dipoles in the reflectarray cells have been optimized to produce a collimated beam in dual polarization in the transmit and receive bands. The measured radiation patterns confirm the high performance of the antenna in terms of bandwidth (27%), low losses, and low levels of cross polarization. Some preliminary simulations at 11.95 GHz for a 1.2-m antenna with South American coverage are presented to show the potential of the proposed antenna for spaceborne antennas in Ku-band.

A hybrid technique for analyzing corrugated and noncorrugated rectangular horns

A hybrid technique is proposed to solve the entire problem of corrugated and noncorrugated rectangular horns without the usual approximations. The horn antenna is simulated by a multistepped waveguide structure radiating into half-space. The procedure is composed of three steps. First, assuming the horn to be terminated by infinite metallic flange, the aperture problem is accurately solved by a hybrid modal-spectral method (HMSM). Second, the modal analysis (MA) method and scattering matrix concept of waveguide discontinuities are employed to solve the transverse multidiscontinuity problems. Finally, the two methods are combined (MA-HMSM) to solve the entire problem of the horn antenna. The proposed technique allows to obtain not only the radiation patterns, but also the reflection and near-field characteristics of the horn, without any restriction on the geometry (semiflare angles, profiled horn contours, corrugations). A good agreement between theoretical predictions and experimental results has been obtained for several horns.

Design of a 1-metre reflectarray for DBS application with 15% bandwidth

A one-meter reflectarray has been designed for a DBS European coverage in a 15% frequency band (10.95- 12.75 GHz). The reflectarray is made of three stacked layers of printed arrays with rectangular patches. The dimensions of the staked patches are optimised in each element to ensure the required coverage at live frequencies in the working band. The radiation patterns fulfil the contour requirements for both H- and V- polarisation in the required frequency band.

Accurate and Efficient Modeling to Calculate the Voltage Dependence of Liquid Crystal-Based Reflectarray Cells

Two models that can predict the voltage-dependent scattering from liquid crystal (LC)-based reflectarray cells are presented. The validity of both numerical techniques is demonstrated using measured results in the frequency range 94-110 GHz. The most rigorous approach models, for each voltage, the inhomogeneous and anisotropic permittivity of the LC as a stratified media in the direction of the biasing field. This accounts for the different tilt angles of the LC molecules inside the cell calculated from the solution of the elastic problem. The other model is based on an effective homogeneous permittivity tensor that corresponds to the average tilt angle along the longitudinal direction for each biasing voltage. In this model, convergence problems associated with the longitudinal inhomogeneity are avoided, and the computation efficiency is improved. Both models provide a correspondence between the reflection coefficient (losses and phase-shift) of the LC-based reflectarray cell and the value of biasing voltage, which can be used to design beam scanning reflectarrays. The accuracy and the efficiency of both models are also analyzed and discussed.

Design and Demonstration of an Electronically Scanned Reflectarray Antenna at 100 GHz Using Multiresonant Cells Based on Liquid Crystals

The design, fabrication, and measured results are presented for a reconligurable reflectarray antenna based on liquid crystals (LCs) which operates above 100 GHz. The antenna has been designed to provide beam scanning capabilities over a wide angular range, a large bandwidth, and reduced side-lobe level (SLL). Measured radiation patterns are in good agreement with simulations, and show that the antenna generates an electronically steerable beam in one plane over an angular range of 55° in the frequency band from 96 to 104 GHz. The SLL is lower than -13 dB for all the scan angles and -18 dB is obtained over 16% of the scan range. The measured performance is significantly better than previously published results for this class of electronically tunable antenna, and moreover, verifies the accuracy of the proposed procedure for LC modeling and antenna design.

Design manufacture and test of Ka-band reflectarray antenna for trasmitting and receiving in orthogonal polarization

This contribution describes the design, manufacturing and test of a printed reflectarray for a Ka-band terminal antenna. The reflectarray has been designed to produce a focused beam at 30 GHz (uplink) in V polarization and also at 20 GHz (downlink) in H polarization. Two separate feeds are used to illuminate the reflectarray for H (20 GHz) and V polarization (30GHz). The reflectarray element is made of two stacked varying-sized patches, being one dimension adjusted to focus the beam at 20 GHz in H polarization, and the other to focus the 30 GHz beam in V-polarization. A breadboard has been manufactured and tested. The measured radiation patterns show very good agreement with those obtained from the simulations. A 10% bandwidth has been obtained in both frequency bands, with an antenna efficiency of 62% at 30 GHz and 70% at 20 GHz

A Transportable Reflectarray Antenna for Satellite Ku-band Emergency Communications

The design of a Ku-band reconfigurable reflectarray antenna for emergency satellite communications is presented. Bidirectional high data rate satellite links are needed in emergency conditions where other telecommunication infrastructures are not available. In order to operate in this type of scenario, an antenna should be deployable, transportable, and easily repointable. The need of an automatic and fast satellite location and pointing system leads to a completely electronic reconfigurable antenna. The operative bandwidth is from 10.7 to 12.5 GHz for reception and from 14 up to 14.5 GHz for transmission (30% of relative bandwidth). The selected antenna architecture is based on a dual reflectarray system comprising a passive subreflectarray and an active main reflectarray made of reconfigurable 1-bit elementary cells based on PIN diodes.