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.
Index Terms-Antennaarrays, antenna optimization, moment methods, Radial Line Slot Array (RLSA) d λ apart, making an angle of 45±° with respect to the radial direction ( Fig. 1) [7]. Since the two slots in the
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.
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 Maxwell's 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.
Although slot antennas are usually modeled as\ud
perfectly electric conductors, for accurate antenna design and\ud
optimization, ohmic loss effects cannot be neglected. This is especially\ud
true in millimeter and submillimeter-wave applications, and\ud
in low-cost technology for mass production, where highly conductive\ud
surfaces are out of budget. This paper presents a rigorous but\ud
efficient method-of-moments (MoM) formulation for the analysis\ud
of radial line slot array (RLSA) antennas, which includes the finite\ud
conductivity of metals. First, by using equivalence and reciprocity\ud
theorems, effective magnetic currents are defined on each slot\ud
aperture, instead of standard electric and magnetic equivalent\ud
currents. This choice halves the number of unknowns of the MoM\ud
linear system, still preserving the rigor of the electromagnetic\ud
formulation. Next, proper Green’s functions accounting for the\ud
finite conductivity of metals are derived analytically and used\ud
in the MoM admittance matrix expressions. A numerical check\ud
of self and mutual admittances for a couple of slots etched in\ud
a nonperfectly conducting structure is provided against results\ud
from a finite-element method. Finally, a few RLSA realizations\ud
are analyzed to investigate the effect of ohmic losses in a practical\ud
antenna design
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