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In this letter, we present a design of a linear array of tilted dipoles to achieve radiation patterns with asymmetric angular filtering characteristics. To realize the asymmetric radiation, the dipole elements are spaced by a distance larger than half a wavelength, thus allowing for grating lobes to occur in the visible region. Moreover, the dipoles are loaded with artificial dielectrics to increase the front-to-back ratio and consequently to enable higher gain in certain desired angular regions. Based on the design, a linear array with ten elements is manufactured and tested. The measured results show the ability of such an array to achieve stable gain from broadside up to 90° scanning while implementing a stopband angular filter for negative scanning angles., Tera-Hertz Sensing

Antenna arrays located on airplanes or other mobile platforms for satellite communication applications are typically required to support very large scan angles (close to end-_re). How- ever, planar antenna arrays are typically characterized by scan loss. To increase the scan range conformal arrays and multi-panel configuration can be found in literature, but the height of the structures is still too large to be installed on airplanes without significant impact on the aircraft drag. To obtain wide-scan capability while still maintaining a low antenna profile, hybrid scanning mechanism are currently implemented (F. Tiezzi et al., Eu- CAP, 2010). The idea is to scan the beam electronically from broadside to a positive, as high as possible, angle and then to achieve the full coverage by mechanical rotation of the array along the azimuth. In this work we present a study to determine the parameters affecting the power radiated in specific directions by antenna arrays with tilted elements. We developed an efficient Method of Moments (MoM) for the analysis of linear arrays with arbitrarily tilted dipole elements, in free space or in the presence of a backing reflector. By using this analysis method, we study the radiation characteristics of arrays of stacked dipoles over a ground plane, highlighting the variation of the patterns as a function of the inter-element distance and the angle of inclination of the element. For half wavelength inter-element distance the array pattern is rather symmetric even for tilted elements, as expected from the Floquet theory (A.K. Bhattacharyya et al., IEEE TAP, 51, 1572-1581, 2003). However, when the elements are tilted by positive angles and for inter-element distance larger than half wavelength, a null and a reduction in directivity in the radiation pattern is achieved for negative scanning angles. Grating lobes in the visible region are weighted by element pattern. The minimum of the radiation pattern is not necessarily aligned with the d, Tera-Hertz Sensing

We present the design of an array of tilted dipoles loaded with artificial dielectrics, to achieve asymmetric radiation patterns. First, a simplified array element consisting of skewed stacked dipoles in the presence of a backing reflector is studied, by means of a dedicated spectral periodic method of moments (MoM). The analysis of the stacked dipoles provides guidelines to design arrays with certain radiation characteristics, by varying the tilt angle and the inter-element spacing. Based on the findings of numerical analysis, we then propose a tilted dipole element design with artificial dielectric loading to implement the pattern asymmetry. The design includes the feeding structure and the balun transition to a 50-Ohm coaxial line., Tera-Hertz Sensing

We propose a systematic approach to describe planar slot antennas, embedded in generic stratified media. An equivalent transmission line model for the slot is proposed, based on a spectral domain analysis. First, we introduce a method of moments solution to model semi-infinite slots, fed by a deltagap excitation. The solution entails only two basis functions, one located at the feed and the other at the termination. The latter basis function is chosen to properly account for the field diffractive behavior at the antenna end point. An approximate circuit model is then introduced, which describes the main mode propagating along the slot as an equivalent transmission line. Lumped impedances are extracted to accurately describe the source and the end point. This procedure can be used to derive the input impedance of planar antennas with arbitrary length in generic layered media or the interaction between multiple feeds within the same slot., Tera-Hertz Sensing

A 24 GHz antenna design for miniaturized FMCW radar is presented. The antenna was manufactured with additive manufacturing technology at TNO. The characterization of the polymer material used in the fabrication was carried out and the measurement results of the antenna are presented in this work. A good agreement between simulations and measurements was achieved. © 2018 European Microwave Association.

In this contribution, a focal plane array (FPA) at submillimeter wavelengths is presented for security applications. The detectors are based on kinetic inductance bolometers. Two frequency selective absorber (FSA) sets were designed to implement a security imager. The effective pattern of the imager coupled to a black body point source over a wide frequency band (1:6) was demonstrated experimentally with excellent agreement to the one estimated by using a Fourier optics based technique., Tera-Hertz Sensing

Passive imaging cameras at sub-millimeter wavelengths with large format focal plane arrays are being developed as the next generation of security screening systems. In this contribution, a dual-band focal plane array (FPA) for security imagers at submillimeter wave frequencies is presented. The detectors are based on bolometric superconducting kinetic inductance resonators, which allows the development of large FPAs at medium cooled temperatures. Two frequency selective absorber (FSA) sets coupled to superconductive resonator lines are designed to implement a dual color security imager. The performance of the dual band imager is evaluated using spectral analysis approach that combines Fourier optics with a Floquet mode field representation. The geometry of the unit cells is based on a Jerusalem cross configuration and the designed FSAs show a stable angular response and a rejection 1 to 3 of the undesired bandwidth. The detectors in the dual band FPA are distributed over a hexagonal grid to maximize their physical size and then improve their sensitivity. The effective point spread function of the imager coupled to a black body point source over a wide frequency band (1:6) was demonstrated experimentally with excellent agreement to the one estimated by using the proposed spectral technique., Accepted Author Manuscript, Tera-Hertz Sensing

A five-layer frequency selective surface (FSS) composed of subwavelength elements with large harmonic rejection bandwidth is presented. The FSS design is based on an equivalent circuit model, where the interlayer interaction is only described with a single transmission line representing the fundamental Floquet wave. A prototype of the designed FSS is fabricated, and the measured response exhibits good stability over a wide conical incidence range up to 45°. The FSS is combined with a wide-scanning connected array of dipoles to implement a phased array with integrated filtering properties. A dispersion analysis is performed to define the distance between the array and the FSS that avoids the propagation of surface waves between the combined structures, allowing to maximize the radiation efficiency. The performance of the array combined with the FSS is experimentally characterized, showing high-order harmonic rejection better than 17 dB over a large bandwidth., Accepted Author Manuscript, Tera-Hertz Sensing

A wide field of view (FOV) inversely magnified dual-lens system for submillimeter wavelength imagers is presented in this paper. The antenna is designed for near-field focusing, at a range of 2.1 m from the primary aperture and to work in the frequency range from 200 to 600 GHz. The half-power beamwidth (HPBW) is 0.27° (1 cm in the image plane) at 500 GHz, corresponding to a focused antenna directivity of approximately 55 dBi. The FOV is as large as ±25.4° (±1 m at the nominal range), corresponding to a scan range of ±100 HPBWs. The shapes of the lens surfaces are optimized to minimize the phase aberration loss over the entire scanning range. Moreover, the lenses are designed to be as thin as possible to limit the dielectric absorption loss. The directivity reduction of the edge pattern with respect to broadside is approximately 1 dB with efficiency of 56%, making this lens an excellent candidate for imaging applications. The dual-lens system can be refocused by displacing the secondary lens and shows an essentially unchanged angular HPBW over a refocusing range of ±50% with respect to the nominal imaging distance. A demonstrator was fabricated and the experimental results at 500 GHz confirm the predicted performance., Tera-Hertz Sensing

In this paper, the practical tradeoffs for designing submillimeter wavelength imagers based on optomechanical systems combined with focal plane arrays (FPAs) are presented. The architecture of these systems differs for operation at short and long ranges. General formulas to derive the effective field of view of diffraction limited quasi-optical systems in these two scenarios are shown. These formulas can be used to evaluate the performance of a specific optical system implementation. As an application example, we present the design of an optomechanical system that can operate at both ranges in a modular approach. The presented implementation achieves an effective field of view, which is 70% of the canonical one. The proposed solution consists of a linear FPA of eight active transceivers combined with a raster scan technique. The system for short-range scenario is a side-fed dual-reflector Dragonian architecture because of its good scanning performance when illuminated by an FPA. Thanks to the system's small aperture, the scanner is arranged after the primary mirror, without causing additional scan loss. The Dragonian system is then used to illuminate a confocal dual-reflector architecture to magnify its aperture, and can be used in the long-range scenario. The scanner in this case is before the main aperture and it has to be considered in the performance optimization of the optical system since it adds phase aberration loss., Tera-Hertz Sensing

The aim of the European project CONSORTIS is the development of a walk-by imaging system for concealed object detections working at submillimetre-wave frequencies. This imager will allow to image a full body at two frequency bands with high sensitivity (<;1K) and large frame rate (10Hz). The imager relies on a large focal plane array with about 10k detectors operating at both bands coupled a common optical system. This contribution describes the optimization of the quasi-optical system for this imager. The proposed architecture is based on a novel flipped dual-lens design with a scan loss of less than 3dBs for both bands. This scan loss corresponds to resolution loss of only a factor 1.4 at the edge of the field of view (FoV)., Accepted Author Manuscript, Tera-Hertz Sensing