Alexander B. Yakovlev

In this paper, the cloaked slot antennas (CSAs) in a circular conducting cylinder have been proposed, numerically studied, and fundamentally characterized with respect to the pulsed radar aspects. The two cylindrically slotted antennas have been introduced, namely the axially slotted cloaked antenna and the circumferentially slotted cloaked antenna (CSCA). These two cloaked slot antennas have been parametrically studied to explore the antenna’s resonant characteristics together with their cloaking performance. The resonant frequency of the antennas is controlled by the parameters of the aperture of the slot such as width and length, while independently cloaking the CSAs at the cloaking frequency controlled by the parameters of the coated metasurface. The characteristics of the dual-mode operation at resonant and cloaking frequencies have been intensively studied by pulsed radar signal processing. The modulated Gaussian pulse with the modulation frequency being either resonant or cloaking frequency is used as an excitation source. Several scenarios have been proposed and studied to characterize the cloaking performance and communication capacity of the cloaked slot antennas. The radiating pulse from the CSAs has been numerically characterized by a pulse radar signal processing with an interval of 22.5° in terms of the theta and phi polarizations. These two CSAs have directive and omnidirectional characteristics in the theta- and phi-polarization, respectively.

An electromagnetic cloaking approach is employed with the intention to curb the destructive effects of mutual interference for rectangular and circularly shaped patch antennas situated in a tight spacing. Primarily, we show that by coating the top surface of each patch with an appropriately designed metasurface, the mutual coupling is considerably reduced between the antennas. Furthermore, the cloak construct is extended to a tightly spaced, interleaved linear patch antenna array configuration and it is shown that the coated metasurfaces successfully enhance the performance of each array in terms of their matching characteristics, total efficiencies and far-field realized gain patterns for a broad range of beam-scan angles. For rectangular patches, the cloaked Array I and II achieve corresponding peak total efficiencies of 93% and 90%, in contrast to the total efficiencies of 57% and 21% for uncloaked Array I and II, respectively, at their operating frequencies. Moreover, cloaked rectangular Array I and II exhibit main lobe gains of 13.2 dB and 13.8 dB, whereas uncloaked Array I and II only accomplish main lobe gains of 10 dB and 5.5 dB, respectively. Likewise, for the cloaked circular patches, corresponding total efficiencies of 91% and 89% are recorded for Array I and II, at their operating frequencies (uncloaked Array I and II show peak efficiencies of 71% and 55%, respectively). The main lobe gain for each cloaked circular patch array is approximately 14.2 dB, whereas the uncloaked Array I and II only achieve maximum gains of 10.5 dB and 7.5 dB, respectively.

Electromagnetic cloaking approach is employed with the intention to curb the destructive effects of mutual interference for rectangular and circularly shaped patch antennas situated in a tight spacing (sub-wavelength separation is employed). Primarily, we show that by coating the top surface of each patch with an appropriately designed metasurface, it is possible to considerably reduce the mutual coupling between the said antennas. We also demonstrate that, despite the close proximity of these patches, the individual radiation characteristic of each antenna is reinstated to emulate their performance in an isolated scenario. Furthermore, the cloak construct is extended to a tightly spaced, interleaved linear patch antenna array configuration and it is shown that the coated metasurfaces successfully enhance the performance of each array in terms of their matching characteristics, total efficiencies as well as their far-field realized gain patterns for a broad range of beam-scan angles. The decoupling and cloaking action of these metasurfaces are demonstrated by various full-wave numerical simulation results. We believe that the simple planar structure of our metasurface design (according to simulation models) makes it feasible for fabrication and the fact that it is used to accomplish cloaking of an electrically large antenna surface, makes it unique in itself.

We have proposed an effective metasurface design to accomplish the cloaking of equilateral patch antennas and their array configuration. As such, we have exploited the concept of electromagnetic invisibility, employing the mantle cloaking technique with the intention to eliminate the destructive interference ensuing between two distinct triangular patches situated in a very congested arrangement (sub-wavelength separation is maintained between the patch elements). Based on the numerous simulation results, we demonstrate that the implementation of the planar coated metasurface cloaks onto the patch antenna surfaces compels them to become invisible to each other, at the intended frequencies. In effect, an individual antenna element does not sense the presence of the other, in spite of being in a rather close vicinity. We also exhibit that the cloaks successfully reinstate the radiation attributes of each antenna in such a way that it emulates its respective performance in an isolated environment. Moreover, we have extended the cloak design to an interleaved one-dimensional array of the two patch antennas, and it is shown that the coated metasurfaces assure the efficient performance of each array in terms of their matching as well as radiation characteristics, which in turn, enables them to radiate independently for various beam-scanning angles.

In this paper, we have proposed an effective metasurface design to accomplish cloaking of equilateral patch antennas and their array configuration. As such, we have exploited the concept of electromagnetic invisibility, employing the mantle cloaking technique with the intention to eliminate the destructive interference ensuing between two distinct triangular patches situated in a very congested arrangement (sub-wavelength separation is maintained between the patch elements). Basically, we demonstrate that implementation of the planar coated metasurface cloaks onto the patch antenna surfaces compels them to become invisible to each other, at the intended frequencies. In effect, an individual antenna element does not sense the presence of the other, in spite of being in a rather close vicinity. We also exhibit that the cloaks successfully reinstate the radiation attributes of each antenna in such a way that it emulates their respective performance in an isolated environment. Moreover, we have extended the cloak design to an interleaved one dimensional array of the two patch antennas and it is shown that the coated metasurfaces assure efficient performance of each array in terms of their matching as well as radiation characteristics, in turn, enabling them to radiate independently for various beam-scanning angles.

Most of the theoretical studies involving graphene, typically assume an ultra-high mobility and/or high value of Fermi energy to achieve exciting functionalities such as polarization conversion, absorption, cloaking, among others. In practice, however, graphene with such high mobility is very difficult to realize, on account of the numerous flaws and impurities that inevitably are introduced during the graphene growth and transfer process. This severely compromises graphene’s practical performance, despite the appeal of theoretical predictions. A novel design was presented in ‘X. Wang et al , IEEE Trans. Antenna Propagat., vol. 67, pp. 2452–2461, 2019’, wherein a graphene metasurface was devised to accomplish perfect absorption with excellent electrical tunability, for a wide span of practical mobility values for graphene (2,000 to 20,000 cm ² V ^-1 s ^-1 ). Motivated by this design, in this paper, we introduce a graphene-metal metasurface structure, which is engineered to facilitate the realization of practical cloaking of conducting cylindrical objects. Though the framework for our cloak is ostensibly similar to the metasurface structure in the aforementioned reference, the phenomenon that our structure is based on, is radically different; consequently, the functionality and the numerical analysis differs. When this specific metasurface is enveloped around the cylindrical objects, their scattering width reduces noticeably, thereby making them ‘invisible’ to the impinging plane wave. Our design demonstrates cloaking even for the most practical low-mobility graphene, utilizing extremely low Fermi energy values, thereby making our construct desirable not only in theory, but also feasible for practical applications.

In this letter, we endeavor to curb the adverse effects of mutual coupling between two-slot antennas (operating at C-band frequencies), situated at a subwavelength separation. The effects of mutual coupling become extremely apparent at such close proximity and leads to the deterioration of the radiation aspects of each antenna. To mitigate these detrimental effects, we exploit the concept of mantle cloaking for the design of specialized cloaks, consisting of elliptical dielectric regions integrated with capacitive metallic strips. It is demonstrated through simulation results that by enclosing each radiating edge of the individual slots with these uniquely designed metasurfaces, the slot antennas are decoupled in the near field. Moreover, the metasurface cloaks also facilitate restoration of the far field radiation properties of the slots. In this regard, our cloak design ensures that the slot antennas do not sense the presence of each other, enabling each slot antenna to operate individually, as if they were isolated.

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This work studies the propagation characteristics of a rectangular waveguide with aligned/misaligned double-sided dielectric-filled metallic corrugations. Two modes are found to propagate in the proposed double-sided configuration below the hollow-waveguide cutoff frequency: a quasi-resonant mode and a backward mode. This is in contrast to the single-sided configuration, which only allows for backward propagation. Moreover, the double-sided configuration can be of interest for waveguide miniaturization on account of the broader band of its backward mode. The width of the stopband between the quasi-resonant and backward modes can be controlled by the misalignment of the top and bottom corrugations, being null for the glide-symmetric case. The previous study is complemented with numerical results showing the impact of the height of the corrugations, as well as the filling dielectric permittivity, on the bandwidth and location of the appearing negative-effective-permeability band. The multi-modal transmission-matrix method has also been employed to estimate the rejection level and material losses in the structure and to determine which port modes are associated with the quasi-resonant and backward modes. Finally, it is shown that glide symmetry can advantageously be used to reduce the dispersion and broadens the operating band of the modes.

In this work, we present a numerical study of 1D and 2D closely spaced antenna arrays of microstrip dipole antennas covered by a metasurface in order to properly cloak and decouple the antenna arrays operating at neighboring frequencies. We show that the two strongly coupled arrays fed by a microstrip-to-balanced transmission-line transition are effectively decoupled in 1D and 2D array scenarios by covering the dipole antenna elements with an elliptically shaped metasurface, which comprises sub-wavelength periodic metallic strips printed on an elliptically shaped dielectric cover around the dipole antennas and integrated with the substrate. We present a practical design of cloaked printed dipole arrays placed in close proximity of each other and demonstrate that the arrays are decoupled in the near field and operate independently in the far field with their original radiation characteristics as if they were isolated.