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 strictly causal numerical study of the pulsed operation of a weakly dispersive, leaky wave (LW) antenna is presented. The intricacies at the forefront of the electromagnetic (EM) field radiated from a gap-fed slot in a perfectly electrically conducting (PEC) sheet are evidenced for the first time. The radical effect of a free-space gap separating the PEC sheet from the dielectric half-space into which the slot radiates is demonstrated, thus providing time-domain (TD) arguments for the effectiveness of this essential element of leaky-lens antennas (LLAs). The response of the gapped structure to an excitation consisting of pulse trains is evaluated. The discussed results pave the way toward building a genuine TD counterpart of the LW radiation from gap-fed slots. Furthermore, they are conditional to understanding the transients occurring in between intervals when a steady-state, time-harmonic (TH) operation can be assumed, an extremely relevant ingredient to implementing highly complex modulations in carrier-based, wireless transfer.

Photo-conductive antennas (PCAs) are the workhorse of time-domain THz sensing and imaging. In this work, we employ a rigorous Norton equivalent circuit model to identify and estimate the substrate-related parasitic effects, that might limit the THz emission, to better design future PCAs.

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.

A spectral domain analysis aimed at studying dipoles radiating in layered media is presented. The model allows for the modeling of the non-zero metal thickness and the reactance associated with a Δ-gap excitation. The solution can be efficiently calculated with a semi-analytical procedure, and it is linked to an equivalent circuit representation. The results show an accuracy up to par with commercial solvers regarding the input impedance and the radiated far field patterns.

In the circuit theory, the Norton and Thevenin equivalent generators are tools that simplify the solutions of networks involving passive or active components. They have been extensively used in the frequency domain to describe time-harmonic sources. A time-stepped evolution is instead typically used to include transient sources. As a particular case of the latter, the Norton equivalent circuit is extended here to investigate pulsed photoconducting sources, where a dc bias voltage and a pulsed optical laser are combined to generate terahertz (THz) bursts. The proposed derivation relies on the application of the electromagnetic (EM) equivalence theorem. The main conclusion of this derivation is the understanding that, from the three different spectral regions (dc, THz, and optics), only the THz radiation is to be explicitly included in the equivalent circuit. The theory is validated by a campaign of measurements reported in a connected paper.

In this work, we investigate antenna architectures to implement dual-mode operation in phased array designs. Planar slot antenna elements are used in array configuration, in combination with artificial dielectrics layers (ADLs) located in the close proximity of the array, to achieve pattern shaping. The artificial dielectric superstrate supports the propagation of leaky waves that can be optimized to enhance the gain in a specific angular region or to enlarge the array field of view. By controlling the amplitude and phase of the antenna elements, the radiation patterns can be combined to realize either wide or narrow beams. This concept present advantages for both millimeter-wave (mm-wave) communication and radar applications. A design of a four-element array fabricated in standard printed circuit board (PCB) technology validates the feasibility of the dual-mode operation. The measured results also show good agreement with simulations.

Drude's description of the response of low-temperature gallium arsenide to optical pulse excitation is used to evaluate the components of a time-domain Norton equivalent circuit of a photoconductive antenna (PCA) source. The saturation of the terahertz (THz) radiated power occurring at large optical excitation levels was previously associated by the scientific community to radiation and charge screening of the bias. With the present circuit, we are able to model accurately the measured saturation as only due to the EM feedback from the antenna to the bias. The predicted THz radiated power is shown to match very accurately the measurements when the circuit is combined with an accurate description of the experimental conditions and the modeling of the THz quasi-optical (QO) channel.

State-of-the-art THz pulsed commercial systems operating over large bandwidth suffer from high dispersion or low radiation efficiency due to the poor coupling between the transmitter and receiver photoconductive antennas (PCAs). In this work, we present the fabrication and characterization of a leaky-lens PCA that has the potential to solve this problem. The presented PCA is based on a low-temperature grown gallium arsenide (LT-GaAs) membrane with a 1:15 bandwidth coverage (0.1-1.5 THz), where the frequency response is constant. In order to fabricate the PCA on an LT-GaAs membrane, a novel fabrication process is developed. This process is dramatically faster than previously used processes (∼1.5 h instead of ∼20 h). Furthermore, an experimental validation of the radiated power together with the comparison to a standard bow-tie-based PCA fabricated on the same LT-GaAs wafer is shown in this article. We show that the PCA source on the LT-GaAs membrane is more efficient due to the enhanced leaky wave radiation. The leaky-lens PCA stands out as a great candidate to improve the coupling efficiency in THz pulsed commercial systems, where the maximum laser power that can be used is limited by the dispersion in the optic fiber.

We present a study on beam coupling in radiating structures that support multiple simultaneous beams. The formation of multiple beams is relevant in modern wireless communication applications when diverse data streams can be sent from a single transmitter to users located in different directions. General expressions are provided that relate the coupling between radiated beams to the associated current distributions on the radiating aperture. When expanding the currents in terms of basis functions, the beam coupling can be also written in terms of coupling contributions due to each pair of basis functions. The analysis is applied to antenna arrays with different levels of mutual coupling between the array elements. More specifically, arrays of resonant elements, characterized by very low mutual coupling, are compared with arrays of connected elements, which are strongly coupled. We show that, even for a very high level of mutual coupling between individual array elements, it is possible to obtain orthogonal beams if the total current distributions associated with the beams are uncoupled.

The number of independent links that can be hosted by an antenna platform for Line-of-Sight (LoS) communications is limited by its physical size and the interference between the beams associated with different users. For large-size platforms, the interference can be reduced by compromising the aperture efficiency, and this trade-off is the metric to quantify the effective use of the platform. This metric fails for antenna platforms that are not electrically large, for which the aperture efficiency is no longer a useful parameter. Here we resort to the concept of the Observable Field, related to the maximum theoretical directivity, to estimate the potential number of independent links supported by moderate-size platforms. This allows the introduction of coupling coefficients between the beams associated with the observable portion of the incident field and the beams associated with the receiving antennas. These coefficients are bounded to unity for any platform dimension, unlike the aperture efficiency, and they are maximized when the antenna pattern is equal to the pattern predicted by the Observable Field. Accordingly, selecting beams dictated by the Observable Field constitutes a benchmark for the effective use of the volume. Any antenna design can be compared to this benchmark to assess its merits.