A novel high-gain dielectric resonator antenna (DRA), featuring a peak realized gain of 11.3 dBi over a fractional bandwidth of 16.6% around 30 GHz, is presented. The proposed antenna structure, excited by a slot coupled microstrip line, is composed of a cylindrical dielectric resonator and of a truncated plastic-based conical horn useful to enhance the gain. An annular perturbation notch is realized in the dielectric horn to achieve a better focusing of the RF energy along the antenna boresight direction, while reducing the side-lobe levels (SSLs). The presented antenna design achieves SSLs below -10 dB for both the E- and H-plane so to meet the requirements of next-generation 5G wireless communication protocols and of low-cost satellite and mobile systems.

Compact high-gain wideband antenna systems for through-the-wall imaging and wireless communications, featuring 160% fractional bandwidth, are presented. Each radiating system, consisting of two orthogonal Vivaldi antennas forming a cross-shaped configuration so to excite linear (horizontal/vertical) and circular polarization (CP), is equipped with a top-mount spherical-axicon dielectric lens. The optimized shaping of the lens and of the outer edge Vivaldi arms allow achieving gain levels exceeding 15dBi with good front-to-back-ratio. The proposed antenna features a broadside gain diagram with stable radiation pattern and wideband impedance matching in the frequency range between 650 MHz and 6 GHz. CST Microwave Studio®, implementing a full-wave locally conformal finite integration technique (FIT), was employed to design and characterize the antenna and to guide its physical realization. Two-port equivalent circuits were developed to characterize parasitic coupling effects between the Vivaldi antennas ports, while a full-wave analysis allowed characterizing their frequency and time domain behaviors. The numerical results concerning the antennas parameters, illustrating the suitability of the proposed antennas to support narrow and ultra-wideband signal waveforms, are found to be in good agreement with the experimental measurements performed on an antenna prototype.

Microwave imaging is an active area of research that has garnered interest over the past few years. The main desired improvements to microwave imaging are related to the performances of radiating systems and identification algorithms. To achieve these improvements, antennas suitable to guarantee demanding requirements are needed. In particular, they must operate in close proximity to the objects under examination, ensure an adequate bandwidth, as well as reduced dimensions and low production costs. In addition, in near-field microwave imaging systems, the antenna should provide an ultra-wideband (UWB) response. Given the relevance of the foreseen applications, many UWB antenna designs for microwave imaging applications have been proposed in the literature. In this paper, a comprehensive review of different UWB antenna designs for near-field microwave imaging is presented. The antennas are classified according to the manufacturing technology and radiative performances. Particular attention is also paid to the radiation mechanisms as well as the techniques used to reduce the size and improve the bandwidth.

A fast low-cost through-the-wall radar imaging (TWRI) system, based on a vector network analyzer (VNA), a couple of switches and an array of Vivaldi antennas, has been designed, realized, and tested. To solve the TWRI inversion problem, an original theoretical modeling for a class of TWRI techniques whose basic functions are the cross-range Fourier transform (FT) of the scattered field and its covariance operator has been proposed. Using these functions, four conventional algorithms, namely the delay and sum (DAS), the FT, the multiple signal classification (MUSIC), the hybrid DAS-MUSIC and a new algorithm, the hybrid FT-MUSIC, have been derived. All these techniques have been implemented and their accuracy and field of view have been tested on canonical scatterers. Then, the algorithms have been applied to measured data collected in different scenarios constituted by a metallic bar or a human subject in the absence and in the presence of a wall between the antenna and the considered targets. Using the proposed TWRI system, it has been possible to detect a subject located up to 5-m away from the radar antenna array through a tuff wall. The proposed FT-MUSIC algorithm has evidenced performances similar to those of the DAS-MUSIC but with significantly lower execution times. Finally, FT-MUSIC performances in terms of field of view and immunity to disturbances are better compared to those of the MUSIC algorithm.

A wideband high-gain dielectric horn-lens antenna (DHLA) for wireless communications and UWB applications, featuring 122% fractional bandwidth, is presented. The antenna, consisting of a dielectric horn equipped with a spherical-axicon dielectric lens that increases and equalizes the gain within the operating band, is placed on a PCB featuring a wideband 8-shaped slot fed by a tapered microstrip line employed to excite the radiating system. The lens, integrated within the body of the dielectric horn, has the property of focusing the RF energy near its vertex on an extended frequency band, thus ensuring compact size, excellent field coupling with the antenna excitation system, and a significant increase of antenna gain. The antenna operates in the 3-12.4 GHz frequency range with relatively flat group delay, making it suitable for operating with narrowband, broadband, and impulsive UWB signals. The antenna can work properly without or with a metal reflector useful to enhance gain (up to 19 dBi), improve the front-to-back ratio, and reduce the impact of the antenna characteristics from the installation site. CST Studio Suite™, implementing a full-wave locally conformal finite integration technique (FIT), was employed to design and characterize the antenna. The antenna characteristics estimated numerically were found to be in good agreement with the experimental results performed on an antenna prototype.

An energy-based representation suitable for the electromagnetic characterization of linear multi-port circuits and antenna systems, as well as for the optimization of antenna beam forming and near-field RF-focusing performances, is presented. Radiation, ohmic, dielectric power loss and reactive power storage are described in concise matrix form, yielding respective eigenmodes and eigenfields that rigorously account for all energetic processes. Noteworthy eigenfields orthogonality properties are illustrated and employed to maximize (minimize) active power flow through, or to synthesize fields on, arbitrary surfaces. Applications of the proposed formulation include multiport antennas, microwave sensing devices, microwave hyperthermia applicators, through-the-wall imaging and wireless power transfer (WPT) systems. Numerical results illustrate features and performance advantages of the proposed formulation as applied to multi-port antennas, and lead to define some basic design guidelines.