Waqas H. Syed

Closed-Form Analysis of Artificial Dielectric Layers—Part II: Extension to Multiple Layers and Arbitrary Illumination

In this second part of a two-paper sequence, we present an analytical formulation to model artificial dielectric layers (ADLs) of finite height. We extend the method developed in Part I (IEEE Trans. Antennas Propag., vol. 62, no. 12, pp. 6256-6264, 2014) describing the single layer to the multilayer case, by including the higher-order interaction between parallel sheets in analytical form. From the equivalent impedance of the layers, we can construct a transmission line model that provides the spectral Greens function of ADLs in closed form. This allows to characterize the propagation through finite ADLs and to study the dispersion characteristics from the investigation of the Greens function singularities. Finally, by integrating the responses of a continuous set of plane waves, sources at finite distances from the ADL slab are treated. The method is validated by comparison with commercial electromagnetic solvers and experimental results obtained from a X-band prototype demonstrator.

Front-to-Back Ratio Enhancement of Planar Printed Antennas by Means of Artificial Dielectric Layers

In this paper, we investigate the use of artificial dielectric layers (ADLs) as a mean to enhance front-to-back radiation ratio in printed, planar antennas. These artificially engineered substrates can be designed to be anisotropic and present high dielectric constants for the waves propagating orthogonal to metallic layers. However, the dielectric constants is as low as that of the host material for the waves that propagates towards grazing direction, and thus surface waves due to multiple reflections at the dielectric air interface are not enhanced. A simple qualitative description of this concept is followed by the presentation of a experimentally verified prototype which clearly highlights the potential advantages of the proposed ADL for antenna applications.

Closed-Form Analysis of Artificial Dielectric Layers—Part I: Properties of a Single Layer Under Plane-Wave Incidence

This two-part sequence of papers deals with the analysis of artificial dielectric layers (ADLs). ADLs consist of a cascade of planar periodic surfaces designed to realize dielectric slabs with a desired equivalent permittivity. A single layer is typically composed of an array of electrically small patches periodically arranged in a rectangular lattice. In this paper we present an analytical formulation to model a single layer for arbitrary plane-wave incidence, highlighting the characteristic properties and their frequency range of validity. We derive a closed-form solution for the magnetic current distribution, including the reactive near field on the crossing slots, by expanding the total current with ad-hoc entire-domain basis functions. Simple analytical expressions are also derived for the equivalent sheet impedance of the layer. The second part of the paper extends the analysis to finite ADL slabs and nonplane wave sources.

Design, Fabrication, and Measurements of a 0.3 THz On-Chip Double Slot Antenna Enhanced by Artificial Dielectrics

In this paper, we demonstrate, at 300 GHz and with integrated technology, the effectiveness of artificial dielectric layers to enhance the front-to-back ratio of printed antennas. This concept was previously proposed at microwave frequencies and using printed circuit board technology. The artificial material is now realized by introducing non-resonant metallic inclusions in a silicon dioxide host material. This allows to enhance the permittivity of the host medium and renders it anisotropic. By loading an electrically thin dielectric with these metallic inclusions, an engineered slab with effectively quarter wavelength thickness has been realized. Despite the large effective height and density of the artificial dielectric, the surface wave efficiency of the antenna is 99%. This is entirely due to the anisotropic properties of the material. A prototype antenna was built using an in-house CMOS back-end compatible integrated circuits (IC) process. Measured results from the antenna are presented and show a good agreement with the expected results.

Wideband, Wide-Scan Planar Array of Connected Slots Loaded With Artificial Dielectric Superstrates

Microwave broadband wide-scan antenna arrays are typically implemented resorting to vertical arrangements of printed circuit boards (PCBs). Here, we propose a planar solution realized with a single multi-layer PCB, with consequent reduction in cost and complexity of the array. It consists of an array of connected slots backed by a metallic reflector and loaded with superstrates. Artificial dielectric layers (ADLs) are used in place of real dielectrics to realize the superstrates, as they are characterized by very low surface-wave losses. For the unit-cell design, we developed an analysis tool based on closed-form expressions and thus requiring minimal computational resources. Finite-array simulations are also performed by generalizing the analysis method to account for the truncation effects. The presence of the ADL superstrate allows reducing the distance between the array plane and the backing reflector while maintaining good matching performance. A realistic feed structure is also proposed, which consists of a microstrip line connected to a coaxial feed. Such a solution does not require balanced-to-unbalanced transitions, which often limit the achievable bandwidth. The proposed structure achieves in simulations more than an octave bandwidth (6.5-14.5 GHz), within a scanning range of ±50° in all azimuth planes.

Artificial dielectric layers for the performance enhancement of slot antennas on a dielectric lens

In this work the concept of Artificial dielectric layers (ADL) has been utilized for the design of integrated slot antennas. ADL possess inherent property of enhancing the dielectric constant of the host dielectric materials, over extremely wide frequency ranges. They are realized by means of periodic metallic stratifications in a standard dielectric substrate. For the proof of concept, ADL have been used as an add-on component between a standard dual slot antenna and a dielectric lens. More than an octave of -10 dB impedance bandwidth has been achieved. The far-field radiation patterns are usable over approximately 60% of the impedance bandwidth.

Equivalent Transmission Line Models for the Analysis of Edge Effects in Finite Connected and Tightly Coupled Arrays

In this paper, we present an analysis of the edge effects in wideband connected arrays of slots and dipoles. Due to the strong mutual coupling between the elements, these arrays can support the propagation of guided waves along their surface. Such waves arise from the edges of the finite array and can be especially detrimental to the performance, since they can travel within the array without geometrical spreading. In this paper, we introduce Green’s function-based equivalent transmission line models to describe the propagation of the guided waves. The elements’ active impedances are represented as periodic loads on these transmission lines. The equivalent models can be used as a simple and convenient tool to control and minimize the edge effects. Finite array simulations of relevant array structures are discussed. The evidence is that the active impedance and the interelement capacitance can be tuned to attenuate and reflect the edge-born waves.

A planar wideband wide-scan phased array: Connected array loaded with artificial dielectric layers

We present a novel concept for wideband, wide-scan phased array applications. The array is composed by connected-slot elements loaded with artificial dielectric superstrates. The proposed solution consists of a single multi-layer planar printed circuit board (PCB) and does not require the typically employed vertical arrangement of multiple PCBs. This offers advantages in terms of complexity of the assembly and cost of the array. We developed an analytical method for the prediction of the array performance, in terms of active input impedance. This method allows to estimate the relevant parameters of the array with a negligible computational cost. A design example with a bandwidth exceeding one octave (VSWR<;2 from 6.5 to 14.3) and scanning up to 50 degrees for all azimuth planes is presented.

A CMOS-compatible metamaterial to enhance the front to back radiation ratio in terahertz antenna for sensing application

Here we report for the first time the fabrication of a high aspect ratio, IC compatible metamaterial that greatly enhances the sensing performance of antennas in the Terahertz frequency. The metamaterial is realized by means of multilayered periodic metallic inclusions inside a thick dielectric host matrix. When placed on top of the radiating structure, this metamaterial increases the front-to-back radiation ratio by more than 10 dB, ensuring the matching of the antenna from 280 to 325 GHz. The maximum temperature reached during fabrication is 400°C, thus making this approach suited as CMOS back-end process.

A 5:1 connected slot array loaded with artificial dielectric layers

We propose a radiation concept to realize phased arrays with wideband and wide-scanning performance. The array is based on connected-slot elements that radiate in the presence of artificial dielectric superstrates. The array can be implemented with a single multi-layer printed circuit board. Artificial dielectrics are used in place of real dielectrics to minimize the losses due to surface waves and avoid the occurrence of scan blindness over a wide scan range. The achievable bandwidth depends on the number of layers composing the artificial dielectric. A design example is shown that achieves a bandwidth (VSWR<2.5) of about 5:1 when scanning up to 50° in all azimuth planes. Both single- and dual-polarization designs can be implemented.