Planar wide-scan wideband phased arrays with improved polarization purity

One of the common requirements for wideband wide-scanning arrays in multifunctional platforms is the polarization agility. Cross-polarization levels should be kept low within the entire field of view and frequency band of operation. However, good polarization purity is hard to achieve especially for arrays that are designed to operate over multi-octave bandwidth. Planar wideband array often use dielectric slabs above the antenna aperture to improve the matching while scanning and increase the front-to-back ratio. However, dielectric superstrate deteriorate the polarization performance on the diagonal planes. The characteristic cross-polarization of a connected slot array in the presence of artificial dielectric layers superstrates is analyzed. An approach to reduce the cross-polarization is then investigated, consisting of localizing the artificial dielectric only in specific regions of the unit cell, rather than on the entire area. Index Terms–Artificial dielectric layers, connected arrays, cross-polarization, wideband arrays, wide-scanning arrays.Tera-Hertz Sensin

Parallel Plate Waveguide Feeding Structure for Planar Connected Arrays

A novel approach for the practical realization of the feeding lines in connected array of slots is presented. The proposed feed concept is based on a parallel-plate waveguide (PPW) structure and allows simplifying the unit cell design. When compared to the typical integrated coaxial feed, the PPW-based feeding structure can reduce the cost and complexity of the array, by resulting in a lower number of metal layers and by allowing for large diameter vias. Two examples of the unit cell design, based on this new feed concept, are presented; one consists in a single-polarized array of connected slot, covering the band from 70 to 140 GHz; another example is referring to a single- and dual-polarized connected slot array covering the 2-8 GHz range.Tera-Hertz Sensin

Analysis of Artificial Dielectric Layers with Finite Conductivity

In journal: FERMAT(ISSN 2470-4202), Volume 31, Communication 5, Jan.-Feb., 2019Tera-Hertz Sensin

Analytical equivalent models of artificial dielectric layers with arbitrary inter-layer shifts

Closed-form expressions to describe artificial dielectric layers (ADLs) are presented. The propagation of a generic plane wave within the artificial material is described by means of transmission line models, where each layer is represented as an equivalent shunt impedance. The given analytical formulas for the shunt impedance account for the reactive coupling between the layers due to higher order Floquet modes, thus remain valid even for extremely small electrical distance between layers. The expressions are derived assuming finite conductivity of the metal, thus also an accurate estimation of the losses within the artificial dielectric is obtained from the equivalent circuit.Tera-Hertz Sensin

Dissipation Losses in Artificial Dielectric Layers

Closed-form expressions to describe artificial dielectric layers (ADLs) with finite conductivity are presented. The propagation of a generic plane wave within the artificial material is described by means of transmission line models, where each layer is represented as an equivalent shunt impedance. The given analytical formulas for the shunt impedance are derived assuming finite conductivity of the metal, thus also an accurate estimation of the losses within the artificial dielectric is obtained from the equivalent circuit. The expressions account for the reactive coupling between the layers due to higher order Floquet modes, thus remain valid even for extremely small electrical distance between layers.Accepted Author ManuscriptTera-Hertz Sensin

Applications of Artificial Dielectric Layers for mm-Wave Antennas

Artificial Dielectric Layers (ADLs) have recently been exploited to improve the radiation and impedance performance of integrated antennas at millimeter wave (mmWave) and terahertz (THz) frequencies. The ADLs are composed by layers of sub-wavelength periodic metal patches that can be arranged within a host medium to synthesize an equivalent anisotropic material. Thanks to the availability of closed-form expressions for the modeling, ADLs can be conveniently designed to realize matching layers and impedance transformers when used in the closed proximity of antennas, to improve their bandwidth and the front-to-back ratio. An overview of different applications that benefit from this concept is given. Moreover, recent developments on the use of ADLs for wideband flat lenses are described.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

Recent Advances on Wideband Wide Scanning Connected Slot Arrays

Connected slot arrays with artificial dielectric layers (ADLs) are a type of wideband wide-scanning arrays with several favorable properties. A key advantage is the high front-to-back ratio provided by the artificial dielectric, which allows to reduce the distance between the radiating slots and the ground plane. This results in low-profile array designs the can be realized with multi-layer planar printed circuit boards at microwaves and millimeter waves. Another important feature is the anisotropy of the ADLs, which yields wide scanning capability without supporting the propagation of surface waves. An overview of different array designs based on this concept is given here, together with a description of the typical design steps and the achievable performance. An example unit cell is shown, with 10:1 band, maximum scan angle of 60°, and total height lower than a quarter wavelength at the lowest frequency.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

Design of an efficient 900 GHz antenna in standard CMOS technology for imaging arrays

This paper describes and addresses the challenges that are encountered while designing a 900 GHz antenna for FET detectors using a standard submicron CMOS technology. The reduced metal stack, the problem of surface waves and technology-related rules are taken into account in order to properly design an efficient antenna, with the objective to couple it to field-effect transistor (FET) detectors in a focal-plane array configuration. Simulations on a 0.15-μm standard CMOS technology show that up to 58% efficiency with responsivity in the several kV/W range can be achieved.Accepted author manuscriptTera-Hertz Sensin

Analytical Formulas for Artificial Dielectrics with Nonaligned Layers

In this paper, we present analytical models to describe artificial dielectric layers (ADLs), when a lateral shift between layers is present. The alternate lateral displacement between layers is an important parameter to engineer the desired effective electromagnetic properties of the equivalent homogeneous material realized with the ADLs. More specifically, the equivalent dielectric constants that can be realized by alternatively shifting the layers are higher compared with the aligned case. Closed-form expressions are derived for the equivalent layer reactance that includes the higher order interaction between shifted layers. The given analytical formulas can be used to derive an equivalent circuit model that describes the scattering parameters of a plane wave impinging on a slab composed by an arbitrary finite number of metal layers. To aid the design of artificial dielectric slabs, the effective permittivity and permeability tensors are also retrieved from the scattering parameters.Accepted Author ManuscriptTera-Hertz Sensin

Analysis of Nonsquare Artificial Dielectric Layers and Application to the Design of Anisotropic Slabs

We present a general analysis to describe nonsquare artificial dielectric layers (ADLs). Closed-form expressions for the equivalent layer impedance are given for generic plane-wave incidence, assuming that the ADLs have different geometrical parameters in the {x}-and {y}-directions. The analytical expressions account for the interaction between the layers due to higher order Floquet modes, thus remain valid for arbitrarily small electrical distance between layers. Such nonsquare geometries allow the design of artificial anisotropic slabs with azimuth-dependent effective refractive index. As an example for an application, the equivalent model is used to design the superstrate of a double-slot antenna, with independent pattern shaping in the two main planes.Accepted author manuscriptTera-Hertz Sensin