Connected slot arrays are a type of ultrawideband phased array known for their wide-scanning capabilities. A suitable method to feed the slots is using parallel-plate waveguides (PPWs), which reduce the unit-cell complexity. However, current analytical models for connected arrays are unable to completely model the PPW feed, which usually necessitates a time-consuming design process using commercial antenna simulation tools. In this letter, we present a model for the PPW that incorporates the reactive components introduced by folding the feed. The proposed feed model can be incorporated into existing array models to jointly optimize the unit cell and the feed structure.

This work deals with the efficient analysis of linear arrays of cavity-backed slot antennas. The considered array elements can be single or multiple slots radiating in the presence of a rectangular cavity. A spectral method of moments (MoM) is used to estimate the impedance and the patterns of the slot array. The method is rendered computationally efficient by considering, for each slot, only two basis functions that suitably describe the magnetic current distribution. The first basis function is derived by solving the auxiliary problem where only the cavity walls parallel to the slot axes are considered. The second basis function is obtained by solving the problem of a closed rectangular cavity excited by a magnetic current distributed on the slot region. The proposed method allows to simulate entire finite arrays in a few seconds per frequency point and can be exploited to aid the design and optimization of cavity-backed slot arrays.

We present an efficient method to analyze a periodic pin-patch structure, consisting of two artificial dielectric layers (ADLs) connected by vertical metal pins. ADLs are made of square metal patches in a periodic lattice and have recently been used as superstrates in antennas and arrays to enhance the bandwidth and scanning range. ADLs form an anisotropic effective medium, thus enabling a large scanning volume without supporting surface waves. However, the anisotropy increases the cross-polarization (X-pol) of the antenna in the diagonal plane. This problem can be reduced by introducing vertical metal pins in the ADL superstrate to form the pin-patch structure. The analysis method is based on a spectral method of moments (MoMs) and uses entire-domain basis functions in a hybrid Cartesian and cylindrical representation to accurately model the currents on the structure and scattering parameters under general plane-wave incidence.

A dual-polarized ultra-wideband array prototype operating from 2 to 8 GHz is designed, manufactured, and tested. The array consists of 8 × 16 connected slot elements per polarization, with artificial dielectric layers placed above the slots. The design exploits a feed concept based on parallel plate waveguides, with the goal of improving the manufacturability of the printed circuit board realizing the array. One-to-eight corporate feeding networks are also designed to reduce the number of coaxial connectors. Measured results of the matching and radiation performance are shown to be in good agreement with simulated predictions.

We present a systematic approach to include the effects of dielectric slabs in artificial dielectric layers (ADLs). Typical implementations of ADLs consist of layers of sub-wavelength metal patches supported by either dielectric slabs or thin dielectric films bonded onto foam spacers. The presence of dielectrics in the proximity of the metal layers affects the equivalent layer capacitance and thus must be accurately taken into account for the modeling and design of the ADLs. The proposed procedure allows to derive an analytical expression for the effective permittivity of each capacitive layer that depends on the dielectric layers in the vicinity of the metal. The equivalent layer capacitance can be then included in the ADL equivalent transmission line model, which can be used, for instance, for the design of matching structures in ultra-wideband arrays.

Multi-beam systems are a key technology for the high-speed links of the next-generation communication standards. Due to the stringent space constraints for allocating antennas on a platform, it is of paramount importance to assess - with respect to the physical size - the multi-beam performance of the antenna in terms of the maximum number of simultaneous orthogonal beams. This is done by resorting to the concept of the observable field, which is here extended to planar domains. Then, this concept is used to assess the multi-beam performance of a wideband phased array prototype developed for mobile communications. The Signal-to-Interference Ratio (SIR), computed from the measured radiation patterns of the prototype, is analyzed versus the frequency and the number of beams and compared to the benchmark case of an ideal antenna radiating the observable field.

A review on wideband wide-scanning arrays based on connected slot elements with artificial dielectric superstrates is given. The analysis method to evaluate the active input impedance of the unit cell is described and its application to wideband array designs is discussed. Design examples reaching up to 10:1 bandwidth are presented, including experimental results from prototypes. The typical achieved performance is compared with the state-of-the-art. Aspects such as cross-polarization levels and finite edge effects are also discussed.

We present a dual-polarized connected array of slots with an artificial dielectric layer (ADL) radome for mobile communication applications operating in the sub-6 GHz and the upper 6 GHz bands of 5G. The radiating slots are combined with two interchangeable ADL radomes with different thicknesses, targeting the bands 6-8 and 2-8 GHz, respectively. This highlights the main property of the ADL radome, which realizes an impedance transformer whose bandwidth is proportional to the height of the structure. Moreover, the ADL anisotropy allows for wide scanning, up to 60° in the main planes for both radomes, without scan blindness. An $8\,\, \times \,\, 8$ prototype array has been manufactured and tested with the two ADL radomes. The measured results of the active voltage standing wave ratio (VSWR) and the radiation patterns are reported to validate the design.

We present an approach to design wideband arrays of connected slots with artificial dielectric layers (ADLs) that allows to take into account both matching and polarization properties. The slots are fed by parallel plate waveguides (PPW s) that are co-designed with the ADLs to realize the desired matching bandwidth. An equivalent circuit model of the unit cell is derived, including both the feed and the AD Ls, providing a fast and accurate estimation of both the active reflection coefficient and the cross-polarization level. Such model enables a tradeoff between matching and polarization efficiency already at the early stages of the design.

We present an analytical model to describe arrays of connected slots fed by parallel plate waveguides (PPWs). Connected slot arrays are planar ultra-wideband arrays with wide scanning capability. PPW feeds can be used to reduce the complexity of the unit cell design. However, existing analytical expressions of the active input impedance of the array cannot account for the presence of PPWs. Here, we develop a new model that includes PPW structures in the stratification, enabling the optimization of the design together with the feed. An equivalent circuit of the unit cell is derived, where the PPW sections are represented in terms of equivalent transmission lines for each Floquet mode. Closed-form expressions are also derived for the capacitance associated with step discontinuities of the PPW and the inductance associated with the feed. Full-wave simulations are used to validate the model.

This work aims to provide guidelines on the design of wideband flat lenses based on artificial dielectric layers (ADLs). Planar lenses based on metasurfaces are typically narrowband, due to the phase wrapping over the period of 2\pi that is strongly frequency-dependent. On the contrary, true-time-delay (TTD) planar lenses, which do not resort to phase discontinuities, can achieve large bandwidths. One convenient way to design wideband TTD lenses is by means of ADLs, which are stacks of subwavelength-period patch arrays embedded in a host medium to increase its effective permittivity. Tradeoffs including bandwidth, focal ratio, lens diameter, and thickness are discussed and related to the manufacturing constraints of artificial dielectrics, such as the smallest features realizable in printed circuit board (PCB) technology, which define the maximum achievable effective permittivity. An example of design is also presented, operating from 30 to 60 GHz and experimentally validated.

A semi-analytical method is presented for the design of gradient index (GRIN) flat lenses. Closed-form expressions are derived to define the refractive index distribution of the lens, for several cases: collimating lenses with on-axis feed, collimating lenses with off-axis feed, lenses converting spherical wavefronts with different wavenumbers, lenses changing the focal number of a quasi-optical system, and Fresnel zone lenses. The design equations are validated by ray-tracing simulations in inhomogeneous media, implemented by numerical solution of the Eikonal equation.

The characteristic cross-polarization (X-pol) of wide angle impedance matching (WAIM) structures is investigated. The study considers an ideal linearly polarized current sheet in the presence of various dielectric and artificial dielectric superstrates, analyzed using transmission line models representing the stratified media. The main mechanism that causes increased X-pol is highlighted and linked to the anisotropy of the superstrate. We then propose an approach to reduce the X-pol by including vertical vias within the WAIM dielectrics, to control the vertical component of the permittivity tensor. The intrinsic X-pol performance of a set of artificial dielectric layers (ADLs) with and without vias is experimentally verified by placing the WAIM above an open-ended waveguide that acts as a linearly polarized source. The proposed WAIM with vias can be used in wideband wide-scanning array designs to improve polarization purity.

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