Computation of layered mixed potentials for the accurate and efficient analysis of periodic printed structures

International audienceOriginal acceleration procedures are proposed for the efficient calculation of the vertical components of the dyadic and scalar mixed-potential layered-media periodic Green's functions for various types of periodic structures. The extraction of suitable asymptotic terms, i.e., quasi-static images, is performed in order to speed up the convergence of the relevant spectral series. The extracted terms can be expressed as potentials for array of half-plane and half-line sources, depending on the type of the considered periodic Green's function. The relevant numerical results show the remarkable improvements in the efficiency of the approach

Effects of aperture thickness on the shielding effectiveness of metallic enclosures

The effects of apertures with finite thickness on the shielding effectiveness of rectangular metallic enclosures is investigated through an approximate but efficient formulation based on the method of moments. As expected, the analysis shows that the finite aperture thickness can help to increase the shielding effectiveness of the structure, especially in the high- frequency region. Comparisons with rigorous full-wave results confirm the validity of the proposed technique

A self-matched wide scanning U-stub microstrip periodic leaky-wave antenna

A new type of printed periodic leaky-wave antenna is proposed, which is able to continuously scan a beam from backward to forward endfire. The unit cell consists of a microstrip line loaded with long lengths of transmission line folded as a U-stub and an interdigital capacitor. This U-stub geometry, which is characterized by a compact longitudinal size, permits operation at frequencies lower than other conventional periodic leaky-wave antennas. At the same time, the presence of the interdigital capacitor makes the radiating U-stub discontinuity self-matching, thus allowing for an elimination of open-stopband effects and for an achievement of an almost constant gain while the beam is scanned through broadside. A noteworthy aspect of the present design is that it represents the first periodic leaky-wave antenna that scans through broadside by radiating from the fundamental n = 0 harmonic, without being a quasi-homogeneous metamaterial structure

Broadside radiation properties of 1D microstrip leaky-wave antennas

In this paper the behavior in the neighborhood of broadside for 1D periodic microstrip leaky-wave antennas is investigated. As is well known this type of antenna is characterized by a radiated beam that is frequency scannable from the backward to the forward quadrant; however the presence of an open stopband results in undesirable scan performance near broadside. Here the open stopband is thoroughly characterized and related to different types of discontinuities within the unit cell through a comparison with the results obtained for a strip grating; moreover, a technique is described in order to obtain a minimization of the stopband effects

Full-wave analysis of bound and leaky modes propagating along 2D periodic printed structures with arbitrary metallisation in the unit cell

A full-wave numerical approach for the analysis and design of two-dimensional printed periodic structures on a grounded dielectric slab is presented. Electromagnetic band-gap surfaces, metamaterials and leaky-wave antennas are important special cases of structures that can be analysed. The proposed technique permits the analysis of an arbitrary metallisation within the unit cell; it is based on a mixed-potential integral equation solved by the method of moments in the spatial domain. Two-dimensional periodic vector and scalar Green’s functions are derived in the spectral domain and an appropriate choice of the spectral determination for each spatial harmonic is performed to properly account for leakage effects. The proposed approach is used to calculate the real propagation wavenumber for surface waves in their pass-band regimes, propagating at arbitrary angles on two-dimensional periodic printed structures. Complex propagation wavenumbers can be derived as well for both bound modes in their stop-band regimes and proper and improper leaky modes in their relevant physical and non-physical regions. Results for a reference uniplanar compact photonic bandgap structure are reported demonstrating how the application of this rigorous technique provides a new detailed picture of the different modal behaviours and a more accurate determination of its band-gap zones

Surface-Wave Suppression in a Double-Negative Metamaterial Grounded Slab

In this work, surface-wave propagation in a metamaterial grounded slab is investigated. In particular, a double-negative (DNG) medium is considered. On the basis of the dispersion equations for TE and TM surface waves supported by such a grounded slab, conditions are presented, which ensure the suppression of a guided-wave regime for both polarizations. In contrast with ordinary grounded slabs, two kinds of surface waves (one evanescent only in air, the other evanescent both in air and inside the slab) have to be taken into account. The possible absence of any surface wave makes the considered structure a promising candidate as a substrate for microstrip antennas with reduced edge-diffraction effects and enhanced radiation efficiency

A pi-Matching Network to Eliminate the Open-Stopband in 1-D Periodic Leaky-Wave Antennas

In this paper the problem of obtaining efficient broadside radiation in one-dimensional (1-D) periodic printed leaky-wave antennas (LWAs) is addressed. In particular, a technique for the elimination of the open stopband (OSB) is presented, which is based on a p network that matches the Bloch-wave impedance of the structure to a desired (non-zero) value at broadside. Three different matching conditions are investigated. Their advantages and drawbacks are briefly discussed and the effectiveness of the technique is demonstrated on a real structure

Modal analysis of arbitrary-shaped 2D periodic structures printed on a grounded dielectric slab: Real and complex solutions

In this paper a full-wave numerical approach devoted to modal analysis of planar 2D periodic structures printed on a grounded dielectric slab with arbitrary metallization within the unit cell is presented. The proposed technique is based on a mixed-potential integral equation, solved by the method of moments in the spatial domain. Twodimensional periodic vector and scalar Green's functions are derived in the spectral domain; this permits to properly account for leakage effects by choosing the correct spectral determination for each spatial harmonic. Real propagation constant for surface waves in their pass-band regimes and complex propagation constant both for bound modes in their stop-band regimes and for proper and improper leaky modes can be efficiently derived. Results for a uniplanar compact photonic bandgap structure, demonstrating the capabilities of this approach, are reported in this paper

A novel printed leaky-wave ‘Bull-Eye’ antenna with suppressed surface-wave excitation

We propose a novel microstrip leaky-wave antenna, based on a multiple-ring ('bull-eye') structure, with a high radiation efficiency and reduced edge-diffraction effects. Such favorable properties are achieved by properly choosing the relevant physical and geometrical parameters in order to operate the antenna in a frequency range in which no surface wave may propagate and the only physical leaky wave is the fundamental TM0 mode. A directive conical radiation pattern, frequency-scannable in a wide angular region, is thereby achieved. Numerical results on dispersion properties of the involved TM and TE modes and full-wave simulations of representative structures are provided to demonstrate the feasibility of the proposed design

Green's Function Calculation for a Line Source Exciting a 2-D Periodic Printed Structure

The electromagnetic field excited by an electric line source in the presence of a printed structure periodic along two directions with arbitrary geometry of the metallization is calculated. The Array Scanning Method (ASM) is adopted to express the field excited by the aperiodic source in terms of an integral superposition of suitable auxiliary Floquet-periodic fields. The latter are solutions of electric-field integral equations that are cast in a mixed-potential formulation in the unit cell and are numerically discretized with an efficient implementation of the method of moments in the spatial domain. The accuracy of the proposed approach is validated through an independent ASM code developed for metal-strip gratings and also against consolidated analytical models available for specific strip- and patch-based periodic structures