1,721,038 research outputs found
A self-matched wide scanning U-stub microstrip periodic leaky-wave antenna
No full textA 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
Full-wave analysis of bound and leaky modes propagating along 2D periodic printed structures with arbitrary metallisation in the unit cell
No full textA 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
Broadside radiation properties of 1D microstrip leaky-wave antennas
No full textIn 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
A novel technique to eliminate the open stopband in one-dimensional periodic printed leaky-wave antennas
No full textIn this paper we deal with the problem of the Open StopBand (OSB) in one-dimensional (1-D) periodic printed Leaky- Wave Antennas (LWAs). In particular, a LWA realized periodically loading a microstrip line with two open-ended stubs per unit cell is considered. The dispersion behaviour of this antenna is analyzed in order to show that a mitigation of the open-stopband effects can be achieved. Moreover, an optimization of its performances near broadside is discussed through a transmission line analysis, changing the distance between the two radiating stubs. Finally, a novel technique to completely eliminate the open stopband is presented. Numerical results for the dispersion behaviour and for the antenna gain are reported to validate both the optimization and the elimination of the OSB
The transition between bound and surface-leaky modes on one-dimensional periodic printed structures
No full textIn this work, the transition between bound and leaky modes on one-dimensional periodic structures
printed on a grounded dielectric substrate is examined for the first time. Such structures support leakage into surface
waves as well as into space due to the presence of the substrate. The solutions in this transition region are calculated
using an accurate full-wave spectral-domain moment-method solution that allows for the determination of both
physical and nonphysical solutions, both of which play an important role in the transition region
Green's Function Calculation for a Line Source Exciting a 2-D Periodic Printed Structure
No full textThe 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
Techniques for scanning through broadside with periodic leaky-wave antennas
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Improved acceleration of mixed-potential periodic Green’s functions through the effective-medium concept
No full textSurface-Wave Suppression in a Double-Negative Metamaterial Grounded Slab
No full textIn 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
Design and characterization of nanostructured frequency-selective surfaces for aerospace applications
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