Semiconductor (SC)-based bulk absorbers operating in the (sub-) THz range are discussed. The conductivities of the bulk media are described by the Drude model for electron gas where the electron density is controlled. The Drude model predicts the existence of two frequencies of interest: one associated with the scattering time of the electrons and a second associated with the plasma frequency. The dimensions of the absorbers for a specific frequency range can be minimized by tuning the doping levels. Eventually, the maximum ohmic absorption from a bulk material is achieved when the real part of the characteristic impedance of the absorber is matched to the one of the surrounding medium and the imaginary part of the characteristic impedance is high so that the power entering the material is actually transformed in heat. Using a classic transmission line representation, a matching layer is introduced to further increase the absorption capabilities of an SC slab. Measurements using a time-domain spectroscopy (TDS) system show the increased accuracy of the Drude model @en

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.@en

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.@en

In this study, an efficient power combiner for mm-wave frequency transmitters is investigated. The combiner is based on a parallel plate waveguide (PPW) excited with multiple parallel feeds. The Doherty power combiner scheme is also integrated in the proposed concept, to increase the efficiency of the amplifiers when implementing amplitude modulation. The advantage of the proposed PPW combiner with respect to other concepts, for example, the ones based on substrate-integrated waveguide, is the wider bandwidth and the scalability to an arbitrary number of inputs. Measured results from a demonstrator realised in standard printed circuit board technology are presented. Two variations of the combiner are implemented, one terminated with a 50 Ω coaxial output, and another integrated with an antenna. In the latter case, the waveguide is folded so that both the power combiner and the antenna fit within a half wavelength size, and thus would be compatible with a dense antenna array implementation.@en

We present a systematic approach to describe planar slot antennas embedded in generic stratified media. An equivalent transmission line model for the slot is proposed, based on a spectral domain analysis. First, we introduce a method of moments solution to model semiinfinite or finite slots, fed by a delta-gap excitation. The solution entails only two basis functions, one located at the feed and the other at the termination. The latter basis function is chosen to properly account for the field diffractive behavior at the antenna end points. An approximate circuit model is then introduced, which describes the main mode propagating along the slot as an equivalent transmission line. Lumped impedances are extracted to accurately describe the source and the end points: The reactances account for the reactive nature of the feed and the termination, while the resistances represent the radiated space waves, emerging from both the feed and the end points. This procedure can be used to derive the input impedance of planar slot antennas with arbitrary length in generic layered media or the interaction between multiple feeds within the same slot.@en

The fifth generation of mobile communication poses challenges in the form of increased data volume, network scalability and efficient network operation. An important part in meeting these requirements is the use of the mm-wave frequency range, enabling the use of a wide bandwidth and therefore the desired high-data rates. However, a challenging aspect of mm-wave communication lies in the efficient generation of RF power. In fact, currently reported power amplifiers are unable to reach the required output power for commercial applications. A typical way to increase the available power is to combine the signal from multiple sources using a power combiner. Power combiners in the mm-wave frequency range have been investigated for many years, but typical problems that occur are area occupation and insertion losses that grow directly with the number of inputs....@en

We present a general analysis to describe non-periodic artificial dielectric layers (ADLs). Closed-form expressions for the equivalent layer impedance are given for generic plane-wave incidence, assuming that each individual layer can differ from the others in terms of geometrical parameters. By dropping the assumption of identical layers, the given formulas are of more general applicability for flexible designs artificial dielectric slabs that are not uniform along the stratification. The analytical expressions account for the interaction between layers due to higher-order Floquet modes, thus remain valid for arbitrarily small electrical distance between layers.@en

We propose a systematic approach to describe pla- nar slot antennas, embedded in generic stratified media. An equivalent transmission line model for the slot is proposed, based on a spectral domain analysis. First, we introduce a method of moments solution to model semi-infinite or finite slots, fed by a delta-gap excitation. The solution entails only two basis functions, one located at the feed and the other at the terminations. The latter basis function is chosen to properly account for the field diffractive behavior at the antenna end points. An approximate circuit model is then introduced, which describes the main mode propagating along the slot as an equivalent transmission line. Lumped impedances are extracted to accurately describe the source and the end points: the reactances account for the reactive nature of the feed and the termination, while the resistances represent the radiated space waves, emerging from both the feed and the end points. This procedure can be used to derive the input impedance of planar antennas with arbitrary length in generic layered media or the interaction between multiple feeds within the same slot. @en

We propose a systematic approach to describe planar slot antennas, embedded in generic stratified media. An equivalent transmission line model for the slot is proposed, based on a spectral domain analysis. First, we introduce a method of moments solution to model semi-infinite slots, fed by a deltagap excitation. The solution entails only two basis functions, one located at the feed and the other at the termination. The latter basis function is chosen to properly account for the field diffractive behavior at the antenna end point. An approximate circuit model is then introduced, which describes the main mode propagating along the slot as an equivalent transmission line. Lumped impedances are extracted to accurately describe the source and the end point. This procedure can be used to derive the input impedance of planar antennas with arbitrary length in generic layered media or the interaction between multiple feeds within the same slot. @en

In this work we present a study to determine theparameters affecting the power radiated in specific directions byantenna arrays with tilted elements. We developed an efficientMethod of Moments (MoM) for the analysis of linear arrays witharbitrarily tilted dipole elements, in free space or in the presenceof a backing reflector. By using this analysis method, we studythe radiation characteristics of arrays of stacked dipoles overa ground plane, highlighting the variation of the patterns as afunction of the inter-element distance and the angle of inclinationof the element. It is shown that, for large arrays (i.e. with morethan 10 elements), the shape of the active element pattern doesnot change significantly as a function of the number of elements,but it depends on the inter-element distance and the skew angleof the array elements. A few examples to show this capabilityare presented.@en

In this work we present a study to determine theparameters affecting the power radiated in specific directions byantenna arrays with tilted elements. We developed an efficientMethod of Moments (MoM) for the analysis of linear arrays witharbitrarily tilted dipole elements, in free space or in the presenceof a backing reflector. By using this analysis method, we studythe radiation characteristics of arrays of stacked dipoles overa ground plane, highlighting the variation of the patterns as afunction of the inter-element distance and the angle of inclinationof the element. It is shown that, for large arrays (i.e. with morethan 10 elements), the shape of the active element pattern doesnot change significantly as a function of the number of elements,but it depends on the inter-element distance and the skew angleof the array elements. A few examples to show this capabilityare presented.@en

Antenna arrays located on airplanes or other mobile platforms for satellite communication applications are typically required to support very large scan angles (close to end-_re). How- ever, planar antenna arrays are typically characterized by scan loss. To increase the scan range conformal arrays and multi-panel configuration can be found in literature, but the height of the structures is still too large to be installed on airplanes without significant impact on the aircraft drag. To obtain wide-scan capability while still maintaining a low antenna profile, hybrid scanning mechanism are currently implemented (F. Tiezzi et al., Eu- CAP, 2010). The idea is to scan the beam electronically from broadside to a positive, as high as possible, angle and then to achieve the full coverage by mechanical rotation of the array along the azimuth. In this work we present a study to determine the parameters affecting the power radiated in specific directions by antenna arrays with tilted elements. We developed an efficient Method of Moments (MoM) for the analysis of linear arrays with arbitrarily tilted dipole elements, in free space or in the presence of a backing reflector. By using this analysis method, we study the radiation characteristics of arrays of stacked dipoles over a ground plane, highlighting the variation of the patterns as a function of the inter-element distance and the angle of inclination of the element. For half wavelength inter-element distance the array pattern is rather symmetric even for tilted elements, as expected from the Floquet theory (A.K. Bhattacharyya et al., IEEE TAP, 51, 1572-1581, 2003). However, when the elements are tilted by positive angles and for inter-element distance larger than half wavelength, a null and a reduction in directivity in the radiation pattern is achieved for negative scanning angles. Grating lobes in the visible region are weighted by element pattern. The minimum of the radiation pattern is not necessarily aligned with the dipole axis but, due to mutual coupling, it can move to different angles depending on the combination of inclination angle and distance. The array directivity is almost at for positive angles up to very large scanning directions, and decreases rapidly at specific negative angles that change with the inter-element distance. Moreover, it is shown that, for large arrays (i.e. with more than 10 elements), the shape of the active element pattern does not change significantly as a function of the number of elements. At the conference considerations concerning the effects on the active element pattern of mutual coupling and of the onset of grating lobes for a given grid size/tilt angle will be presented. Moreover, a linear array design with selective pattern characteristics will be presented. @en