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.

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Low relative permittivity plastic elliptical lenses in combination with integrated focal plane arrays are a promising solution to be used in the future mm- and sub-mm-wave systems. Their appeal lies in the availability of materials with moderate loss and lightweight, and the possibility to use cost-effective manufacturing techniques. However, the achievable scanning angular range is relatively small with low permittivity lenses. In this article, we explore the use of dielectric gratings with modulated height integrated in the lens material, with the aim of enlarging the steering angle. The dielectric gratings synthesize a tilted feed pattern, reducing the reflection loss and spillover when illuminating the lens off-focus. A quasi-analytic approach based on the Floquet mode analysis of the gratings is used to synthesize the grating profile. This method is combined with an analysis in reception of the lens antenna. A wideband prototype in $G$ -band (140-220 GHz) has been fabricated, achieving a field of view of ±25° with gain >30 dBi.

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In this contribution, a broadband G-band leaky-wave (LW) fed lens antenna with an integrated dielectric grid polarizer is presented. The proposed wideband polarizer unit cell geometry enables its fabrication at frequencies higher than 100 GHz, presenting high transmission properties and low axial ratio (AR). A quasi-Analytic technique based on multilayer spectral Green's function combined with a numerical Floquet modes' solver is used to optimize the lens aperture efficiency and AR. The proposed technique is validated via full-wave (FW) simulations. A design is proposed in low dielectric permittivity material, achieving FW simulated aperture efficiency higher than 75% over 44% relative bandwidth, and an AR lower than 3 dB over 35% relative bandwidth. The antenna is able to achieve multiple directive circularly polarized (CP) beams when fed by a focal plane array, preserving the AR bandwidth. A prototype has been fabricated and measured, exhibiting an excellent agreement with quasi-Analytic and FW simulations.

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Future sub millimeter imagers are being developed with large focal plane arrays (FPAs) of lenses to increase the field of view (FoV) and the imaging speed. A full-wave electromagnetic analysis of such arrays is numerically cumbersome and time-consuming. This article presents a spectral technique based on Fourier optics combined with geometrical optics for analyzing, in reception, lens-based FPAs with wide FoVs. The technique provides a numerically efficient methodology to derive the plane wave spectrum (PWS) of a secondary quasi-optical component. This PWS is used to calculate the power received by an antenna or absorber placed at the focal region of a lens. The method is applied to maximize the scanning performance of imagers with monolithically integrated lens feeds without employing an optimization algorithm. The derived PWS can be directly used to define the lens and feed properties. The synthesized FPA achieved scan losses much lower than the ones predicted by standard formulas for horn-based FPAs. In particular, an FPA with scan loss below 1 dB while scanning up to ±17.5° (±44 beam-widths) is presented with directivity of 52 dBi complying with the needs for future sub millimeter imagers. The technique is validated via a physical optics code with excellent agreement.

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In this work, a free accessible MATLAB interface is presented to analyze antenna-coupled Quasi-Optical (QO) systems in reception. This goal is achieved by using Fourier Optics (FO) and Geometrical Optics (GO) based methods. Specifically, the FO method represents the field focalized by a QO component on its focal plane as a plane wave spectrum when the component is illuminated by an incident field. This spectrum is related to the field scattered by the QO component which is calculated here using a GO method. By using this spectrum, the tool estimates the power received by an antenna placed at the focal plane of the QO component. Moreover, the performance in reception is evaluated.

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A high-gain broadband leaky-wave fed lens antenna with an integrated dielectric gratings polarizer covering the whole G-band (140-220GHz) is presented. This work focuses on the polarizer gratings manufacturing and in particular on the selection of plastic materials and the fabrication process refinement. The polarizer geometry has been designed and optimized to be compatible with standard milling techniques. A quasi-analytical method based on an analysis of the lens antenna in reception is used to validate the in-lens polarizer performance. Several prototypes have been fabricated, finally obtaining an excellent match between measurements and quasi-analytical results.

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A novel pulsed photoconductive THz source is presented that is able to radiate mW-level average powers, over a large bandwidth by exploiting both the optical and electrical properties of photoconductive sources and the ultrawideband properties of connected antenna arrays. An optical system composed of a micro-lenses array splits the laser beam into N × N spots that host the active excitation of the antenna arrays. An 'ad hoc' network has been adopted to bias the array active spots in order to implement a connected antenna array configuration. The array feeds a silicon lens to increase the directivity of the radiated THz beam. A slot array prototype has been designed, fabricated, and measured. The proposed solutions achieve excellent power radiation levels by making use of an accurate electromagnetic design. This solution can offer enhancements to any active system relying on pulsed photoconductive antennas.

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DESHIMA is a spectrometer for astronomical applications targeting sources at sub-mm wavelengths from 240GHz to 720GHz that will operate in the ASTE telescope in Atacama Desert, Chile. In this work, a quasi-optical system based on a hyper-hemispherical leaky lens antenna and a series of Dragonian reflectors is presented as the coupling chain for the EM radiation captured by the telescope into the detector. The design procedure is based on a field matching technique in reception. The achieved average illumination efficiency over the band is approximately 70%. The directivity patterns in the sky are also estimated. The side lobe, and cross-polarization levels, over the whole frequency band, are below-16dB, and-18dB, respectively. The measurement of the system is on-going, and will be presented at the conference.

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A pulsed photoconductive terahertz (THz) source is presented that is able to radiate milliwatt (mW) level average power over a large bandwidth, by exploiting both the optical and electrical properties of photoconductive sources and the ultrawideband properties of connected antenna arrays. An optical system composed of a microlenses array splits the laser beam into N×N  spots that host the active excitation of the antenna arrays. An “ad hoc” network is introduced to bias the array active spots in order to implement a connected antenna array configuration. The array feeds a silicon lens to increase the directivity of the radiated THz beam. A dipole and a slot array are designed. Prototypes have been fabricated and measured. Power and spectrum measurements of the prototypes are in excellent agreement with the expected results. The proposed solutions achieve excellent power radiation levels by exploiting accurate electromagnetic design. Thus, they can offer enhancements to any active system relying on pulsed photoconductive antennas.

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Passive imaging cameras at millimeter and submillimeter wavelengths 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. The design of such arrays is typically done resorting to geometrical considerations or basic broadside plane wave incidence analysis. This paper presents a spectral technique for the analysis of such focal plane arrays in reception using Fourier Optics, which is valid also for moderately skewed incident angles. The analysis constitutes a step improvement with respect to previously used methods by providing an accurate and efficient way to estimate the point-source angular response and the throughput from a distributed incoherent source of an absorbing mesh in the focal plane of a quasi-optical component (e.g. a parabolic reflector or lens). The proposed technique is validated with full-wave simulations. After presenting the analysis, the paper compares the performance of arrays of bare absorber in the focal plane of a quasi-optical component to those of corresponding antenna based arrays. It is found that absorbers lead to a comparable trade-off, in terms of spill-over and focusing efficiency, only for very tight samplings. For larger samplings, the focusing efficiency of absorbers is significantly lower than the one for antennas.@en

This second part of two papers' sequence presents the experimental validation of the Norton equivalent circuit model for pulsed photoconductive antennas (PCAs) provided in the first paper of the sequence. To this goal, different prototypes of photoconductive antenna sources have been manufactured and assembled. The average powers radiated and their pertinent energy spectral densities have been measured. In order to obtain a validation of the original equivalent circuit proposed, an auxiliary electromagnetic analysis of the complete setup, including the quasi-optical (QO) link for the signals from the antenna feeds to the detectors had to be developed. By using the combined theoretical model (circuit and quasi-optics), an excellent agreement is achieved between the measured power and the power estimated. This agreement fully validates the circuit model, which can now be used to design new PCAs, including optical and electrical features of the semiconductor materials, as well as the details of the antenna gaps and the purely QO components.

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A novel equivalent circuit for pulsed photoconductive sources is introduced for describing the coupling between the photoconductive gap and the antenna. The proposed circuit effectively describes the mechanism of feeding the antenna by the semiconductor when this latter is illuminated by a laser operating in a pulsed mode. Starting from the classical continuity equation, which models the free carriers' density with respect to the laser power pump and the semiconductor features, a Norton equivalent circuit in the frequency domain is derived. According to the Norton theorem, the equivalent source representation is decoupled from the antenna. In particular, for photoconductive antennas (PCAs), the Norton circuit takes into account of the electrical and optical properties of the semiconductor material, the features of the laser excitation, as well as the geometrical dimensions of the gap. The presence of the electrodes around the gap is part of the antenna and, therefore, it is taken into account in the antenna impedance. The proposed circuit allows the analysis of the coupling between the photoconductive source and the antenna, providing a tool to analyze and design PCAs.

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The exponentially increasing demand for highspeed wireless links can be only efficiently satisfied with the development of future XG wireless communication networks, based on higher carrier signal frequencies, starting from 100 GHz. In this contribution, a circularly polarized G-band leaky-wave fed lens antenna with an integrated dielectric grid polarizer is presented, which can fulfill the challenging requirements for these future XG networks. A design is proposed in low dielectric permittivity material with a feed matching better than -10dB over a 44 % of relative bandwidth. The circularly polarized lens aperture efficiency is higher than 75% over a 35 % relative bandwidth, with an axial ratio lower than 3dB. Analytical tools have been applied to optimize the lens aperture efficiency, validating the results via full wave simulations. A lens prototype has been now fabricated and is currently being measured.

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Optically pumped pulsed THz emitters exploit the transient motion of photo-generated charge carriers in semiconductors, to produce, coupled to micro-antenna, radiated power over a wide bandwidth up to the THz frequencies. The radiation performance of the antenna greatly affects dispersion of the energy spectrum generated by the photoconductive source and if not properly designed it causes low radiated power. This work presents the design, the fabrication process, the electromagnetic and the thermal analyses of a pulsed photoconductive micro-antenna based on the leaky lens antenna concept. This device shows high radiation efficiency over a band ranging from 0.1 to 1.5 THz, thus being a suitable emitter for THz time-domain sensing system.

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A very flexible and efficient iterative physical optics (IPO) algorithm is presented for analyzing the electromagnetic (EM) scattering of complex and electrically large problems. The algorithm accounts for multiple interactions between the objects comprised in the scenarios under the physical optics (PO) approximation. Various techniques for accelerating and parallelizing the algorithm were used, thus obtaining an efficient tool that can be used in novel high-frequency solvers.

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In this paper, a fast iterative physical optics (FIPO) algorithm is proposed for analysis of scattering from electrically large objects involving multiple reflections. When the scenario to be analyzed is electrically very large, a Fast Far Field Approximation (FaFFA) algorithm, based on a domain decomposition of the scatterer surface, can be conveniently used to greatly speed-up the calculation of the induced currents at each step of the iterative procedure. In this work, an efficient and accurate interpolation scheme has been combined to the standard FaFFA algorithm implementation further reducing the complexity of the computation.

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A novel solution for the manufacturing of a reflectarray antenna with cosecant-squared radiation pattern is presented. The unit cell simply consists of a 3-D printed nylon grid inserted in between two thick metallic plates. To introduce the required phase delay, C and reverse C slots are laser cut into the plate illuminated by the feeder. This solution allows obtaining an efficient, robust, and compact antenna with low-cost manufacturing process, even for no mass production. Measurements confirm the feasibility of the proposed solution and show its performances.

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In this paper a rigorous electromagnetic characterization of the setup for measuring the THz power radiated by pulsed photoconductive antenna is discussed. Such characterization is expressed in terms of efficiencies which quantify how much power is lost in the coupling between the various components involved in the measurement setup. The conducted analysis highlights how such efficiencies affect the energy spectrum of the measured pulsed signal. Measurement results with two different detectors will be shown during the conference and will be compared against the power estimation obtained by a recently developed equivalent circuit model for photoconductive antennas. The proposed electromagnetic modeling allows us to effectively improve the design of THz time domain systems.

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A novel Norton equivalent circuit model for characterizing the photoconductive feed of photoconductive antennas is introduced. It incorporates the physics of the photoconductive antenna's excitation by accounting for: (i) the electrical properties of the photoconductive material; (ii) the features of the optical power excitation; (iii) the geometrical dimensions of the gap between the electrodes that couple the antenna to the photoconductive material. The model is applicable to describing the antenna feeding mechanism for the photoconductors being illuminated by means of lasers operating in both pulsed and continuous modes. The proposed model is validated by comparing the power estimated by it with power measurements of different photoconductive antennas. The advocated solution is conducive to analyzing and designing photoconductive antennas. In particular, it is expected to be at the core of antenna optimization tools for maximizing the Terahertz (THz) power radiation, this making it an important enabler for designing THz time-domain systems.

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The most recent developments of an efficient Iterative Physical Optics (IPO) algorithm for analyzing the electromagnetic scattering of complex and electrically large scenarios are presented. The algorithm predicts multiple interactions between the objects comprised in the scenarios under the Physical Optics (PO) approximation. Various techniques for accelerating and parallelizing the algorithm have been used, thus obtaining an efficient tool that can be used to realize a novel class of high-frequency solvers.@en