This paper analyzes the tracking performance of a 94-GHz monopulse feed receiving two simultaneous beams: a circularly - polarized sum beam, and a difference beam generated from the first higher-order mode of circular waveguide. The experimental radiation diagrams of the prototype are processed in amplitude and phase to calibrate suitable polynomial estima-tors for both angles of arrival. It is shown that very simple linear estimators can be used for accurate tracking of both angular coordinates inside the 3-dB beamwidth of the sum beam. Moreover, the tracking model has been extended to cover the 10-dB beamwidth, and used to illustrate the monopulse processor outputs for several target trajectories.

This article presents the first demonstration of a full-waveguide feed at W-band, enabling transmit–receive duplexing and 2-D tracking of targets. The proposed device is a compact unit designed to be used as feed of a 94 GHz space-borne radar. Its duplexing concept relies on a septum orthomode transducer polarizer for transmitting and receiving sum signals with opposite circular polarizations. Additionally, the first higher order mode of circular waveguide (TM01) is allowed to propagate inside the device to extract a difference signal for tracking. By comparing received sum and difference signals in amplitude and phase, both angular directions of a target position can be derived. A prototype of the duplexer was fabricated and tested: measurements at 94 GHz show return loss and isolation above 23 dB at all ports, with reasonable performance from 92 to 96 GHz. The measured monopulse characteristic enables 2-D tracking of targets deviated by less than 8.5° from boresight.

One planar 18 x 18 cm(2) reflectarray prototype, capable of generating adjacent pencil beams with the orthogonal circular polarizations (CPs) in the Ka-band (19.2-20.2 GHz), has been designed, manufactured, and measured as a proof-of-concept to demonstrate the possibility of beam separation in the dual-CP applications. The prototype exhibits main beams pointing at elevation angles of 16.7 degrees and 21.3 degrees for left-hand CP and right-hand CP, respectively. A 1.5 dB gain variation and 66% of efficiency are achieved in the frequency band 19.2-20.2 GHz for a design center frequency of 19.7 GHz. These results will be useful for the future work, involving the design of multispot dual-CP and dual-band planar reflectarrays.

This paper describes the design and some technological developments for a 94-GHz heterodyne chirp radar prototype for space debris detection. We use off-the-shelf components for both the signal generation and the acquisition subsystems, and W-band GaN solid-state technology for the high-power Tx/Rx modules. Several radiating structures are considered in order to expand the system for monopulse tracking operation.

This article demonstrated an accurate analysis technique for dual-reflectarray antennas that take into account the angle of incidence of the impinging electric field on the main reflectarray cells. The reflected field on the sub and the main reflectarray surfaces is computed using Method of Moments in the spectral domain and assuming local periodicity. The sub-reflectarray is divided into groups of elements and the field radiated by each group is used to compute the incident and reflected field on the main reflectarray cells. A 50-cm demonstrator in Ku-band that provides European coverage has been designed, manufactured and tested to validate the analysis technique. The measured radiation patterns match the simulations and they fulfill the coverage requirements, achieving a cross-polar discrimination better than 25 dB in the frequency range: 12.975–14.25 GHz.

A 1.1-m reflectarray antenna has been designed, manufactured and tested to fulfil the requirements of a satellite antenna in Ku-band that provides South American coverage in Tx and Rx. The reflectarray cells consist of four dipoles for each polarization in two dielectric layers, which were selected because of their simplicity and high performance. The dipole dimensions are optimized in all the reflectarray cells to accomplish the prescribed radiation patterns, by iteratively calling an analysis routine based on MoM-SD and local periodicity. The measured radiation patterns of the manufactured antenna have been satisfactorily compared with simulations and with a 3-layer reflectarray previously designed for the same mission.

This paper presents recent developments in Liquid Crystal-based reflectarray antennas for mm-wave applications, future perspectives for this technology and its particular use in SATCOM applications.

We investigate the performance of solidly mounted resonators based on Ir/tilted-AlN/Ir piezoelectric stacks as biosensors. These films are deposited by varying the pressure, the cathode power and the temperature of a two-step process based on depositing (00·2)-tilted AlN active layers over an (10·3)-oriented AlN seed layer. To minimize the influence of the temperature coefficient of frequency on the stability of the biosensor, we use insulating acoustic mirrors made of layers of SiO2 and amorphous TaOx with non-λ/4 thicknesses, which enables to reduce the TCF to −14ppm/°C. The mass loading of the resonators with SiO2 thin films results in a sensitivity of 1800kHz/pg·cm2. Surface functionalization consists on the binding of silane groups on plasma oxidized SiO2 surfaces. After a glutaraldehyde link, streptavidin is bonded to the surface to receive biotinylated receptors for several species. We test thrombin-binding aptamer (TBA29 against thrombin, and IgG antibody against immunoglobulin). The sensors response to species of different molecular weight like TBA-29 (9.75kDa) or IgG antibody (150kDa) is monitored. Finally, we assess the response of the biosensors to different thrombin concentrations (ranging from 4nM to 270nM) on surfaces functionalized with the TBA29 aptamer.

A focused beam and a shaped beam four-layer transmitarray (TA) antenna operating in the K-band have been designed, fabricated, and measured. Four-layer unit cells allowing a transmission phase range of 360 degrees are used. The gain of the beam-focusing TA is 30.3 dB at 19 GHz with an aperture efficiency of 34.9%. Compared with TAs proposed in the literature, the presented antenna bandwidth is almost two times larger with a -1 dB gain bandwidth of 18% and a -3 dB gain bandwidth of 25.5%. A second TA radiating a shaped beam was designed, and its measured pattern correlates well with theoretical calculations. The sensitivity of the proposed unit cells to fabrication errors and the effect of oblique incidence are also studied.

Two dual reflectarray antennas able to provide an European coverage and beam scanning over 8° respectively have been presented. An accurate technique has been proposed for the analysis of dual-reflectarray antennas, which takes into account the angle of incidence of the field impinging on main reflectarray cells. Two 50-cm antenna demonstrators with the same geometry have been manufactured and measured in a compact range. The measured radiation patterns for the contoured beam antenna are in good concordance with the simulations and practically fulfill the coverage requirements with a cross-polar discrimination better than 25 dB in the frequency band 12.975 GHz-14.25 GHz. The measured radiation patterns of the beam scanning antenna are in good agreement with the simulations for transmit and receive frequency bands in Ku-band with a cross-polar discrimination better than 30 dB within a scanning range of ±4°.

A reflectarray antenna capable of operating independently in the transmit frequencies (from a satellite) in Ku-band (11-13 GHz) and Ka-band (19-20 GHz) has been proposed and demonstrated. To prove that independent beams can be optimized in each frequency band using separate feeds, a 25-cm demonstrator that generates a focused beam in dual polarization (linear or circular) has been designed, manufactured, and tested. The reflectarray cells comprise two stacked sets of coupled parallel dipoles for each polarization, which permits an independent optimization of the phase for each frequency and polarization. The simulated and measured radiation patterns for both copolar and cross-polar components are in good agreement in Ku- and Ka-bands.

A novel single layer, dual-polarization reflectarray is proposed to operate at transmit (30 GHz) and receive (20 GHz) frequencies for Ka-band terminal antennas. The proposed reflectarray antenna is based on a unit cell with several resonant elements of adjustable length printed on the same side of a conductor backed substrate. Crossed dipoles and truncated rectangular rings are used to adjust the phase at 30 GHz, while cross-shaped loops are used for the phasing at 20 GHz. The adjustment of phase in each element is made by varying the resonant length of the printed elements. An 18-cm reflectarray antenna with separate feeds for 20 GHz and 30 GHz has been designed and analyzed. The simulated results show satisfactory focused beams with a gain of 30.6 dBi at 20 GHz and 33.7 dBi at 30 GHz.

An accurate technique has been proposed for the analysis of dual-reflectarray antennas, which takes into account the angle of incidence of the field impinging on main reflectarray cells. The technique has been applied to the analysis and design of a contoured beam antenna in Ku-band that provides a European coverage. The reflected field on the sub-reflectarray is computed using Spectral-Domain Method of Moments assuming local periodicity, as customary. The subreflectarray is divided in groups of elements and the radiation from each group is used to compute the incident and reflected fields on the main reflectarray cells. Different degrees of accuracy can be achieved depending on the number of groups considered. A 50-cm antenna demonstrator has been manufactured and measured in a compact range. The measured radiation patterns are in good concordance with the simulations and practically fulfill the coverage requirements with a cross-polar discrimination better than 25 dB in the frequency band 12.975 GHZ - 14.25 GHz.

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.

Two Liquid crystal-based reflectarrays that operate at 100 GHz and 125 GHz are presented. The first pro totype (100 GHz) is used to validate the modeling and the design procedure proposed for this class of antenna. Experimental validation of the beam scanning is carried out by measuring the received power in a quasi-optical test bench, which is able to rotate the receiver in the horizontal plane. These results are used to des ign a second prototype antenna (125 GHz) which exhibits 2D beam scanning capabilities with a large bandwidth and scanning range that is sufficient for radar and communications applications.

ABSTRACTA broadband reflectarray cell made of three parallel dipoles printed on a dielectric layer is presented. A 33% bandwidth is achieved for the cell made of dipoles, which is larger than that obtained for a reference cell consisting of three stacked square patches (26%). Using this cell, a 41‐cm reflectarray antenna has been designed to produce a collimated beam at 9.5 GHz. The numerical results obtained for the reflectarray antenna made of parallel dipoles show a 1‐dB bandwidth of 19%, a 65% efficiency, 0.2 dB of losses, and low levels of cross polarization (25 dB below the maximum). These results demonstrate a high performance for the proposed reflectarray antenna made of cells with three printed dipoles. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:748–753, 2014

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.

Nematic liquid crystals (LC) offer the capability to electronically reconfigure their dielectric permittivity tensor by applying a low AC voltage. This feature can find pertinent applications in submm-wave antenna technology in developing reconfigurable devices. In this contribution we review recent developments for the dielectric characterization of nematic liquid crystal samples at mm wavelengths and describe their applications in reconfigurable reflectarray antenna and tunable linear to circular polarization reflectors. The paper describes the theoretical aspects which underpin the technology that is employed for the realization, packaging and testing.

A reconfigurable reflectarray which exploits the dielectric anisotropy of liquid crystals (LC) has been designed to operate in the frequency range from 96 to 104 GHz. The unit cells are composed of three unequal length parallel dipoles placed above an LC substrate. The reflectarray has been designed using an accurate model which includes the effects of anisotropy and inhomogeneity. An effective permittivity that accounts for the 'real effects' of the LC has also been used to simplify the analysis and design of the unit cells. The geometrical parameters of the cells have been adjusted to simultaneously improve the bandwidth, maximize the tunable phase-range and reduce the sensitivity to the angle of incidence. The performance of the LC based unit cells has been experimentally evaluated by measuring the reflection amplitude and phase of a reflectarray consisting of 52 x 54 identical cells. The good agreement between measurements and simulations validates the analysis and design techniques and demonstrates the capabilities of the proposed reflectarray to provide beam scanning in F band.