Editorial - Incoming EiC

Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Tera-Hertz Sensin

Feasibility Study of Quasi-Optical MIMO Antennas for Radiative Near-Field Links

This article presents a feasibility study of single feed per beam quasi-optical (QO) antennas for enabling incoherent multiple-input multiple-output (MIMO) array front-end architectures at 270 GHz. The objective is to reach ultrafast and radiated energy efficient point-to-point (PtP) wireless links by exploiting the multimode capacity of radiative (Fresnel region) near-field links. In this article, we present a feasibility study of the number of independent links achievable with QO MIMO incoherent arrays. For this purpose, we present theoretical curves of the level of EM co-coupling and interference between the multiple modes versus the link distance. The study focuses at the 252-325 GHz spectral bandwidth defined by the new IEEE 802.15.3d standard. A specific and new MIMO array architecture operating at 270 GHz based on a 2 × 2 array of parabolic reflectors is proposed for a link distance of 100 m. The proposed PtP MIMO system is capable of generating 16 dual-polarized modes in a 70 GHz bandwidth with signal-to-interference ratio >17 dB and a power co-coupling coefficient of -3 dB without the need for interference cancelation techniques. Combining this architecture with wideband front ends could potentially lead to an aggregated data rate in the order of terabit per second in a PtP wireless line-of-sight link, not previously achieved experimentally to the best of authors' knowledge. Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Tera-Hertz Sensin

A Dual-Polarized Leaky Lens Antenna for Wideband Focal Plane Arrays

This paper presents the design and measurements of a wideband dual polarized leaky lens antenna suitable for tightly spaced focal plane arrays. The antenna is composed of two crossed leaky slots fed by two orthogonal microstrips to realize the dual-polarization operation. The crossed microstrips are fed differentially in order to couple the radiation into the slots. The slots are then coupled to a dielectric lens to achieve directive patterns suited for feeding large Focal distance to Diameter ratio reflectors. In this paper, the proposed leaky lens antenna is optimized to achieve high aperture efficiency with clean symmetric patterns in both polarizations exceeding an octave bandwidth. The concept is validated by the measurements of the primary fields inside the lens and with GRASP simulations of the focal plane array.Tera-Hertz Sensin

On the Near-Field Spherical Wave Formation in Resonant Leaky-Wave Antennas: Application to Small Lens Design

In this work, we show that the near field of leaky-wave resonant antennas (LWAs) radiating into a dense medium can be locally represented as a spherical wave in a certain solid angle around broadside using an accurate definition of the phase center. The near field in this solid angle can be efficiently evaluated through the integration of the spectral Green’s function along the steepest descent path (SDP). Beyond this solid angle, defined as the shadow boundary angle, a residual contribution due to the leaky-wave pole must also be added to fully describe the near field. It is found that this shadow boundary angle can be used to define the phase center and geometry of a truncated lens that couples well to leaky-wave antennas, even in electrically small-to-medium sized lenses and low-contrast cases. To demonstrate the applicability of the proposed study, we combine the SDP field calculation with a Fourier optics (FO) methodology to evaluate the aperture efficiency and radiation patterns of small-to-medium sized lenses in reception. A truncated silicon lens with a diameter of only four free-space wavelengths is presented with almost 80% aperture efficiency. Excellent agreement with full-wave simulations is achieved, which demonstrates the accuracy of the proposed design and analysis methodology.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Tera-Hertz Sensin

Radiation of Logarithmic Spiral Antennas in the Presence of Dense Dielectric Lenses

In this paper, the performance of logarithmic spiral antennas as feeds of dense dielectric lens are investigated in detail. The performances are evaluated in terms of clean symmetric radiation patterns, high polarization purity, antenna efficiency, and radiation dispersivity. A logarithmic spiral antenna placed in the dielectric-air interface can provide high aperture efficiencies over large bandwidths if coupled to a synthesized elliptical lens. The use of an air gap increases the directivity of the spiral radiation inside the dielectric allowing for lens directive patterns without sidelobes and reducing the dispersivity of the radiated pulse. The directivity enhancement of the fields inside the dielectric is validated by the measurement of a prototype. The highest frequency at which these antennas can be fed by a planar microstrip line is limited by the thickness of the microstrip substrate.Tera-Hertz Sensin

The Observable Field for Antennas in Reception

In this paper, the portion of the incident field that can be received by an antenna is investigated: the observable field. This field can be estimated relying only on the volume allocated to the antenna and thus independently of the specific antenna geometry. The observable field is composed by a single spherical wave that first converges into the origin and then diverges to infinity. The power associated with the converging wave is the power available to an antenna located within the defined volume. Previously, an estimation of this observable spherical wave was obtained by truncating the spectral spherical modal series representation of the incident field. Here, instead, we provide more applicable approximation of the observable field, by truncating a spatial integral representation of the incident field that is based on the use of equivalent ideal currents. Eventually, for the vast majority of antennas, the estimation of the available power that can be obtained by approximating the observable field via the ideal currents is more accurate than the estimation that would be obtained via the spectral modal expansion. Moreover, analytical expressions for the observable field are provided here. The ideas are set here considering the case of single plane wave incidence, but the extension to multiple plane waves is straightforward.Accepted Author ManuscriptTera-Hertz Sensin

A Shaped Quartz Lens Antenna for Wide Scanning Sub-millimeter Imaging Systems

Lens based focal plane arrays (FPAs) with thousand elements are promising candidates for wide scanning sub-millimeter security imaging systems. To analyze such arrays, a field correlation approach is employed to design an FPA of quartz lenses coupled to a reflector. We consider quartz as the lens material due to its lower cost compared to silicon lenses. Here we focus on the design of the lens element at the edge of the FPA. The reflector’s scanning angle at the edge of its FPA is 20.3°, and the lens surface is shaped to couple better to the reflector. The far-field performance of the optimized shaped lens is validated by full-wave simulations with excellent agreement. The simulated scan loss of the system is 2.6 dB. A prototype was fabricated and will be measured to validate the simulation.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Tera-Hertz Sensin

Analysis of Absorber Based Imaging Systems with Distributed Incoherent Sources

Passive imaging cameras at sub-millimeter wave-lengths are currently entering a new era with the development of large format arrays of direct detectors. Several of these arrays are being developed with bare absorbing meshes without any antenna coupling (lens or horn) structures. This paper uses a spectral electromagnetic model to analyze the performance of absorber based focal plane arrays in comparison to antenna based systems. The methodology is particularly suited to derive guidelines for optimizing the resolution and the sensitivity of thermal imaging cameras at sub-mm wavelengths. The proposed method is validated with full-wave simulations.Accepted Author ManuscriptTera-Hertz Sensin

MIMO Antennas for Radiative Near-Field Links: A Comparative Study at 300 GHz

This paper presents a comparative study of different Multiple Input Multiple Output (MIMO) array architectures to realize high-capacity Point-to-Point (PtP) wireless links for potential use in future 6G backhauling applications. This study focuses on the 220-320 GHz band, defined by the new IEEE 802.15.3d standard. Both phased array and focal plane array architectures are studied, considering the link to operate in the radiative near-field. The theoretically achievable capacities are presented based on the channel matrix estimated in the radiative near-field and the application of Shannon’s capacity formula. It is found that capacities well above Tbps rates can theoretically be realized, even without the use of interference cancellation techniques.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Tera-Hertz Sensin

Wide Field of View Lens-Based Focusing System for Security Imagers at THz frequencies

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 ManuscriptTera-Hertz Sensin