Agnese Mazzinghi

Automatic Design of CP-RLSA Antennas

In this paper a procedure is presented, allowing the automatic design of circular polarized radial line slot antennas, with either pencil or shaped beam patterns. The antenna slot layout is refined by an optimization scheme based on the physical picture behind the working mechanism of the array. The validity of the approach has been proved by designing very efficient pencil beam antennas, either with maximum directivity or with controlled side lobe levels, and a shaped isoflux beam antenna.

Asymptotic Approximation of Mutual Admittance Involved in MoM Analysis of RLSA Antennas

In this paper, a computationally efficient method of moments (MoM) formulation is presented that makes use of an approximate asymptotic formula for the slot mutual admittance. The formula accuracy to the asymptotic order O(r - 3/2) gives sufficient precision for moderate slot distance (1.5-2 wavelengths). In a typical radial line slot array analysis, this permits avoiding the numerical integration in more than 90% of the slot pairs with a savings of CPU time of the same order.

Large Depth of Field Pseudo-Bessel Beam Generation With a RLSA Antenna

The paper discusses the possibility of generating a pseudo-Bessel beam, with a propagation distance of several hundreds of wavelengths in microwave and millimeter frequency band, by using a radial line slot array (RLSA). A specific application for non-contact microwave detection of buried mines has been considered as test case. The design benefits of a holographic approach to assure the required aperture field distribution and makes use of an ad hoc optimization tool to control the antenna slot layout. The predicted and measured antenna behaviors show that high efficiency and polarization purity can be obtained by such a compact and flat antenna, achieving at the same time both manufacturing and setup simplicity.

Influence of the Finite Slot Thickness on RLSA Antenna Design

In this communication, we consider the effect of the thickness of the plate where slots are cut into, with reference to the design of a radial line slot array antenna. We show that the zero-thickness approximation results in a significant lack of accuracy even though the slot thickness is of the order of one-thirtieth of the wavelength. Then, we investigate and compare the accuracy and the efficiency of various approximate numerical techniques that can be conveniently employed in the full-wave analysis and optimization process of the antenna.

Rigorous MoM Analysis of Finite Conductivity Effects in RLSA Antennas

Although slot antennas are usually modeled as perfectly electric conductors, for accurate antenna design and optimization, ohmic loss effects cannot be neglected. This is especially true in millimeter and submillimeter-wave applications, and in low-cost technology for mass production, where highly conductive surfaces are out of budget. This paper presents a rigorous but efficient method-of-moments (MoM) formulation for the analysis of radial line slot array (RLSA) antennas, which includes the finite conductivity of metals. First, by using equivalence and reciprocity theorems, effective magnetic currents are defined on each slot aperture, instead of standard electric and magnetic equivalent currents. This choice halves the number of unknowns of the MoM linear system, still preserving the rigor of the electromagnetic formulation. Next, proper Greens functions accounting for the finite conductivity of metals are derived analytically and used in the MoM admittance matrix expressions. A numerical check of self and mutual admittances for a couple of slots etched in a nonperfectly conducting structure is provided against results from a finite-element method. Finally, a few RLSA realizations are analyzed to investigate the effect of ohmic losses in a practical antenna design.

Comparison between broadband Bessel beam launchers based on either Bessel or Hankel aperture distribution for millimeter wave short pulse generation

In this paper, a comparison is presented between Bessel beam launchers at millimeter waves based on either a cylindrical standing wave (CSW) or a cylindrical inward traveling wave (CITW) aperture distribution. It is theoretically shown that CITW launchers are better suited for the generation of electromagnetic short pulses because they maintain their performances over a larger bandwidth than those realizing a CSW aperture distribution. Moreover, the wavenumber dispersion of both the launchers is evaluated both theoretically and numerically. To this end, two planar Bessel beam launchers, one enforcing a CSW and the other enforcing a CITW aperture distribution, are designed at millimeter waves with a center operating frequency of f¯=60GHz and analyzed in the bandwidth 50 - 70 GHz by using an in-house developed numerical code to solve Maxwells equations based on the method of moments. It is shown that a monochromatic Bessel beam can be efficiently generated by both the launchers over a wide fractional bandwidth. Finally, we investigate the generation of limited-diffractive electromagnetic pulses at millimeter waves, up to a certain non-diffractive range. Namely, it is shown that by feeding the launcher with a Gaussian short pulse, a spatially confined electromagnetic pulse can be efficiently generated in front of the launcher.

Simultaneous Generation of Pseudo-Bessel Vortex Modes With a RLSA

This letter shows that it is possible to simultaneously generate, in the microwave frequency band, several pseudo-Bessel beams having an azimuthal field variation, characteristic of vortex modes, by making use of a single flat antenna. Specifically, a radial line slot array has been designed to prove the concept. The design benefits of a Butler matrix network to provide the correct phase progression along the azimuthal coordinate, and it makes use of a holographic approach to assure the required aperture field distribution.

Double-Spiral Linearly Polarized RLSA

High gain linearly polarized radial line slot arrays (LP-RLSA) suffer from remarkable degradation of the return loss. To overcome this drawback, this communication presents a novel LP-RLSA design obtained by the superposition of two spirally arranged circularly polarized RLSAs. Indeed, it benefits from the intrinsically low reflection coefficient proper of these circularly polarized spirally arrayed RLSAs. Furthermore, the new layout shows high polarization purity, still maintaining the intrinsic manufacturing simplicity of a RLSA antenna. An antenna prototype has been manufactured and measured to validate the design idea.

LP-RLSA Design for Low-Cost Transportable BASYLIS Radar [Antenna Applications Corner]

The increase in small, distributed facilities expected in the near future has raised the necessity of having low-cost, transportable radar systems. In turn, this requires the design of high-gain, low-cost, planar, robust, and easy-to-assemble antennas. In this scenario, the possibility of using a laser-cutting technology in manufacturing a linearly polarized radial-line slot array (RLSA) has been investigated. An ad hoc optimization algorithm, which takes into account the physical mechanism beyond the radial-line slot array antenna, has been developed to obtain low antenna sidelobe levels, as required by the specific BASYLIS radar application. The optimization technique allows using near-resonance radiating slots and canceling slots that are all closely spaced on the upper plate of the radial-line slot array. The measurements carried out on the antenna prototype showed very good performance, despite the use of low-cost materials and manufacturing technology.

Near-Field Focusing by Non-diffracting Bessel Beams

This chapter illustrates the capabilities of non-diffractive Bessel beams for near-field focusing. After a brief introduction of the non-diffractive phenomenon and its origin, the generation of non-diffractive Bessel beams by inward cylindrical traveling waves is analyzed in detail. A ray interpretation is proposed for such beams for infinite and finite radiating apertures. Their main radiation capabilities and limitations in terms of focusing, bandwidth, and operating range are discussed. In particular, it is shown that inward cylindrical traveling wave aperture field distributions can generate non-diffractive Bessel beams over a large bandwidth. As a practical implementation of the discussed theory, a class of launchers based on radial waveguides loaded by metallic gratings or slots is proposed, for which an efficient design and optimization technique is described. In addition, a different and unconventional leaky-wave approach is also adopted for the design of radial waveguides loaded by metasurfaces. The chapter ends by outlining the future research activities and possible applications of non-diffractive beams.