Mauro Ettorre

Multi-Beam Multi-Layer Leaky-Wave SIW Pillbox Antenna for Millimeter-Wave Applications

This work proposes a novel multi-beam leaky-wave pillbox antenna. The antenna system is based on three main parts: feeding part (integrated horns), quasi-optical system and radiating part. The radiating and input parts are placed in two different stacked substrates connected by an optimized quasi-optical system. In contrast to conventional pillbox antennas, the quasi-optical system is made by a pin-made integrated parabola and several coupling slots whose sizes and positions are used to efficiently transfer the energy coming from the input part to the radiating part. The latter consists of a printed leaky-wave antenna, namely an array of slots etched on the uppermost metal layer. Seven pin-made integrated horns are placed in the focal plane of the integrated parabola to radiate seven beams in the far field. Each part of the antenna structure can be optimized independently, thus facilitating and speeding up the complete antenna design. The antenna concept has been validated by measurements (around 24 GHz) showing a scanning capability over ±30° in azimuth and more than 20° in elevation thanks to the frequency scanning behavior of the leaky-wave radiating part. The proposed antenna is well suited to low-cost printed circuit board fabrication process, and its low profile and compactness make it a very promising solution for applications in the millimeter-wave range.

Generation of Propagating Bessel Beams Using Leaky-Wave Modes

The generation of Bessel beams using a leaky radial waveguide is presented. The radial waveguide consists of a capacitive sheet over a ground plane. It supports an azimuthally invariant leaky-wave mode whose normal electric-field component is a truncated, zeroth-order Bessel function. The annular spectrum and nondiffractive extent of the Bessel beam is clearly linked to the complex wavenumber of the leaky-wave mode. The fields inside the radial waveguide are derived using classical vector potential techniques. A vector approach is employed to avoid paraxial approximations of earlier works and the associated limitations on shaping the Bessel beam. Design rules are provided to synthesize a desired propagating Bessel beam. A simple coaxial feed is proposed for the radial waveguide and its input impedance is derived analytically. The analytical results are also validated numerically. The proposed structure and design procedure can be used for generating arbitrary zeroth-order propagating Bessel beams at microwave and millimeter-wave frequencies.

Generation of Propagating Bessel Beams Using Leaky-Wave Modes: Experimental Validation

We present the experimental generation of Bessel beams using a leaky radial waveguide. The radial waveguide consists of a capacitive sheet over a ground plane. The capacitive sheet is composed of patch elements printed on both sides of a dielectric substrate. The radial waveguide is coaxially fed and supports an azimuthally invariant leaky-wave mode whose normal electric-field component is a truncated, zeroth-order Bessel function. Two prototypes are presented with the same propagation constant and lateral extent, but different attenuation constants. 2D electric field measurements and their respective Fourier transforms validate the operation of the prototypes as Bessel-beam launchers at two frequency bands. Cleaner patterns are achieved by the prototype with lower attenuation constant. The dual-band capability and associated frequency dependent resolution can be useful in near-field planar focusing systems. The proposed structure can be used for generating arbitrary zeroth-order propagating Bessel beams at microwave and millimeter-wave frequencies.

Design and Characterization of 60-GHz Integrated Lens Antennas Fabricated Through Ceramic Stereolithography

Three integrated lens antennas made in Alumina and built through ceramic stereolithography are designed, fabricated and characterized experimentally in the 60-GHz band. Linear corrugations are integrated on the lens surface to reduce the effects of multiple internal reflections and improve the antenna performance. The lenses are excited by Alumina-filled WR-15 waveguides with an optimized dielectric impedance matching taper in E-plane. The main characteristics of the first two prototypes with corrugations of variable size are compared to those of a smooth lens without corrugation (third prototype). Experimentally their reflection coefficient is smaller than -10 dB between 55 GHz and 65 GHz, and their radiation characteristics (main beam, side lobe level, cross-polarization level) are very stable versus frequency. In particular, at the center frequency (60 GHz), the total antenna loss (including feed loss) is smaller than 0.9 dB and the radiation efficiency exceeds 80%.

On the Near-Field Shaping and Focusing Capability of a Radial Line Slot Array

We describe the design of a radial line slot array antenna with a shaped and focused near field. The antenna is designed in such a way to control the side lobe level and beamwidth of the normal component of the electric field with respect to the radiating aperture. The design procedure consists of two steps. In the first step, the requirements on the near-field pattern are provided over a focusing plane at a given distance from the radiating aperture. A set theoretic approach is then used to derive the aperture field distribution fitting the requirements over the near field. In the second step, the aperture field distribution is synthesized by accurately placing and sizing the slots of the antenna. The spillover efficiency is maximized during the design process. The antenna is centrally fed by a simple coaxial probe. The antenna design is validated by a prototype and measurements at 12.5 GHz.

Efficient Analysis of Metallic and Dielectric Posts in Parallel-Plate Waveguide Structures

A mode-matching method is proposed for the accurate and fast analysis of structures composed by metallic and dielectric posts in a parallel-plate waveguide environment. The incident and scattered fields on each post are expressed with a cylindrical mode expansion. After enforcing the appropriate boundary conditions, a set of matrix equations is derived. The corresponding solution are the coefficients of the field vector expansion. The method is validated with several examples found in the literature and compared with the results obtained with the commercial software Ansys HFSS. The proposed method can be used for a very fast electromagnetic analysis of substrate integrated waveguides and substrate integrated slab waveguides.

SIW Slotted Waveguide Array With Pillbox Transition for Mechanical Beam Scanning

A dual-layer pillbox antenna is proposed for mechanical beam-scanning applications at millimeter-wave frequencies. It consists of three main subsystems (multislot quasi-optical transition, input part, and radiating part). The input and radiating parts are placed in two different layers, and the quasi-optical transition behaves as a 180° E-plane coupler-type bent. The latter is made of an integrated parabolic reflector and several coupling slots etched in the metal layer located between the two substrates hosting the input and radiating parts. A physical optics analysis of the transition is proposed and compared to full-wave simulations. The radiating part is a planar slotted waveguide array. The input part is an H-plane integrated sectoral horn placed in the focal plane of the parabola and moved along a straight line to obtain the beam scanning. For the horn aligned with the parabola axis, the radiation patterns present half-power beamwidth equal to 6° and 15° in E- and H-plane, respectively. The scan range is ±35°. This mechanical scanning approach represents an attractive solution for those applications where a continuous steering of the main beam is required.

Generation of non-diffractive Bessel beams by inward cylindrical traveling wave aperture distributions

The focusing capabilities of an inward cylindrical traveling wave aperture distribution and the non-diffractive behaviour of its radiated field are analyzed. The wave dynamics of the infinite aperture radiated field is clearly unveiled by means of closed form expressions, based on incomplete Hankel functions, and their ray interpretation. The non-diffractive behaviour is also confirmed for finite apertures up to a defined limited range. A radial waveguide made by metallic gratings over a ground plane and fed by a coaxial feed is used to validate numerically the analytical results. The proposed system and accurate analysis of non-diffractive Bessel beams launched by inward waves opens new opportunities for planar, low profile beam generators at microwaves, Terahertz and optics.

A Full-Wave Hybrid Method for the Analysis of Multilayered SIW-Based Antennas

We propose a fast and accurate full-wave code capable of analyzing electrically large substrate integrated waveguides consisting of stacked parallel-plate waveguides hosting dielectric or metallic posts and coupling and/or radiating slots. Boundary conditions enforced on posts yield scattering amplitudes, while slots are modeled by equivalent magnetic currents, solved by a method of moments. Substantial accelerations are proposed to exploit various symmetries of the structures and to select the optimal number of modes according to the relevant geometrical and physical parameters. The formulation is validated by full-wave simulations with a commercial software and measurement results.

Leaky-wave slot array antenna fed by a dual reflector system

A leaky-wave slot array antenna fed by a dual offset Gregorian reflector system is realized by pins in a parallel plate waveguide. The radiating part of the antenna is composed by parallel slots etched on one side of the same parallel plate waveguide. The dual offset Gregorian reflector system is fed by an arrangement constituted by two vias and a grid, also constituted by pins. Also this feed arrangement realizes a leaky type of radiation, this time inside the parallel plate waveguide. A prototype of the antenna has been designed, manufactured and successfully tested. The low profile, low cost and high efficiency of the antenna render it suited for a variety of radar or telecom applications.