Propagation of nondiffracting pulses carrying orbital angular momentum at microwave frequencies

Abstract

We discuss the generation and propagation of nondiffracting twisted pulses at microwaves, obtained through polychromatic spectral superposition of higher-order Bessel beams. The inherent vectorial structure of Maxwell's equations has been considered to generalize the nondiffracting solution of the scalar wave equation with azimuthal phase variation. Since a wide frequency bandwidth is necessary to synthesize time-limited pulses, the non-negligible wavenumber frequency dispersion, which commonly affects the propagation in the microwave range, has been taken into account. For this purpose, a higher-order Bessel beam is generated by enforcing an inward cylindrical traveling-wave distribution over a finite aperture. We present and discuss the main aspects of the generation of twisted pulses in the microwave range, showing the promising possibility to carry orbital angular momentum through highly focused X-shaped pulses up to the nondiffractive range

A new class of nondiffracting pulses based on focusing leaky waves

“…As is shown in Figs 3(a) and 3(b), the phase constant is limited in the range − 0.47k 0 < β ρ,−1 < −0.18k 0 over the entire bandwidth, whereas the attenuation constant is remarkably regular around the value of α ρ ≃ 0.005k 0 ; such a value fixes the aperture size to ρ ap = 40λ = 20 cm through equation (8).…”

“…It should be stressed that equations (9) and (10) are exact only in the nondispersive case, i.e., θ 0 ( f) = θ 0 , but they still work as lower-bounds for the dispersive case. In general, the minimization of the cone dispersion is highly desirable since it determines the frequency-dependent character of z ndr [through equation 7], which is responsible of the spatio-temporal spreading of XWs: the higher the dispersion, the faster the pulse will broaden as it propagates [7,8].…”

“…therein). Just very recently, theoretical and numerical results have been reported in [7][8][9], whereas experimental results just appeared in [10].…”

Design of Dual Circularly Polarized Sequentially-Fed Patch Antennas for Satellite Applications

“…Circularly polarized (CP) antennas [1][2][3][4] at relatively low frequencies (higher UHF band) have been profitably adopted in several satellite applications such as CubeSats [5,6], MEO satellites [7], telemetry tracking and command (TTC) antennas [8], near-field focusing [9][10][11] only to mention a few. In particular, CP patch antennas combine the advantages of fabrication easiness and of CP: the antenna does not need to be oriented along a particular direction, it is insensible to Faraday rotation, and the channel capacity is inherently duplicated by using the two orthogonal circular polarizations.…”

On the Orbital Angular Momentum Incident Fields in Linearized Microwave Imaging

“…For example, in [18], orbital angular momentum (OAM) incident fields of order higher than = 0, generated through a planar array, were exploited to perform 3D imaging with an observed improvement in the resolution beyond the Rayleigh limit. In [19], sub-wavelength focused near-field (NF) beams and Bessel beams [20][21][22] were proposed to perform imaging in scenarios when possible undesired scatterers are present, and in [23], OAM incident fields were used for accurate recovery of sparse objects through mask-constrained sparse reconstruction.…”