Papers by Homayoon Oraizi
arXiv (Cornell University), Jan 22, 2021
Beyond the scope of conventional metasurface which necessitates plenty of computational resources... more Beyond the scope of conventional metasurface which necessitates plenty of computational resources and time, an inverse design approach using machine learning algorithms promises an effective way for metasurfaces design. In this paper, benefiting from Deep Neural Network (DNN), an inverse design procedure of a metasurface in an ultra-wide working frequency band is presented where the output unit cell structure can be directly computed by a specified design target. To reach the highest working frequency, for training the DNN, we consider 8 ring-shaped patterns to generate resonant notches at a wide range of working frequencies from 4 to 45 GHz. We propose two network architectures. In one architecture, we restricted the output of the DNN, so the network can only generate the metasurface structure from the input of 8 ring-shaped patterns. This approach drastically reduces the computational time, while keeping the network's accuracy above 91%. We show that our model based on DNN can satisfactorily generate the output metasurface structure with an average accuracy of over 90% in both network architectures. Determination of the metasurface structure directly without 1
arXiv (Cornell University), Jul 20, 2020
A circularly polarized leaky-wave antenna capable of frequency scanning is proposed in this paper... more A circularly polarized leaky-wave antenna capable of frequency scanning is proposed in this paper. The main objective is to achieve high gain and polarization purity without the need for a complex feed network. The antenna consists of two independent modules: (1) Anisotropic modulated metasurface antenna (MoMetA) for generating vertically polarized radiation with an operational scanning range of 19 to 47 degrees in elevation; (2) Wide-band polarization converter with high angular stability and capable of converting vertically linear polarization into circular polarization (CP). Aperture field estimation (AFE) method is used to design the antenna with high accuracy in predicting far-field pattern without the need for full-wave simulations. The gain of antenna in the bandwidth of 16 to 21 GHz is obtained better than 18 dBi. Simulation results show that the axial ratio in the maximum gain direction is lower than 3 dB all over its operational frequency bandwidth, demonstrating the proper operation of polarizer. In order to verify the simulation results, one prototype of the antenna is fabricated and its radiation patterns are measured in an anechoic chamber.
arXiv (Cornell University), Oct 23, 2021
In this paper, we present the design procedure of modulated metasurface leaky-wave antennas (MMLW... more In this paper, we present the design procedure of modulated metasurface leaky-wave antennas (MMLWAs) to generate coaxial superposition of vortex beams with several orbital angular momentum (OAM) states. Based on the Flat Optics (FO) technique and aperture field estimation (AFE) method, an analytical framework is proposed to facilitate the implementation of MMLWAs generating multiple topological charges in the OAM regimen. Furthermore, using the spectral analysis which has been derived from the proposed model, we have shown that the symmetry of aperture shape can affect the purity of the mode. Also the perfectly symmetric circular shape is introduced as an ideal choice for high-purity vortex generation. This single aperture antenna with embedded monopole feed can be an appropriate alternative to more complex vortex beam generators such as spiral phase plates and circular antenna arrays.
arXiv (Cornell University), Jul 5, 2020
Ultrawide-angle electromagnetic wave absorbers with excellent mechanical properties are required ... more Ultrawide-angle electromagnetic wave absorbers with excellent mechanical properties are required in many diverse applications such as sensing, and stealth technologies. Here, a novel 3D reconfigurable metamaterial absorber (MMA) consisting of honeycomb and VO2 films is proposed. The proposed MMA exhibits a strong absorptivity above 90% in the widest incident angle up to 87 • for TM-and TE polarized oblique incidences for THz wave propagating in yoz-plane. According to simulation results, under normal incidence, when VO2 films are in the insulating state, the proposed absorber exhibits high absorptivity in the frequency band of 1-4 THz. By increasing the temperature of the whole structure, the structural transformation of VO2 occurs and turns into the metallic phase. We have shown that under oblique incidence, the ohmic losses of VO2 films especially those parallel to the direction of the incident electric field are the most important absorption principles of the proposed MMA. Furthermore, to understand the physical mechanism of absorption, the induced electric field as well as the power loss density of the proposed structure are investigated. In addition, it is shown that the presented VO2 based honeycomb absorber retains its full-coverage incident angle characteristics for TM-polarized incidences propagating in the xoz-plane.
International Symposium on Algorithms and Computation, May 7, 2013
AIP Advances, Sep 1, 2021
In this paper, the concept, analysis, and synthesis of a novel plasmonic leaky wave antenna (LWA)... more In this paper, the concept, analysis, and synthesis of a novel plasmonic leaky wave antenna (LWA) based on the modulated radius of a cylindrical graphene waveguide (CGW) at the terahertz band are presented. Devices based on the planar graphene waveguide (PGW) suffer from high attenuations, which significantly limit the radiation efficiency and beam width of LWAs. It is shown here that the LWA based on CGW compared to PGW can decrease the beam width from 55 ○ to 12 ○ and increase the radiation efficiency from 20% to 50%. A sinusoidally modulated graphene surface is employed to excite the leaky wave antenna. A sinusoidally modulated reactance surface is realized by the modulation of the radius of the cylindrical waveguide. In comparison to other structures, the proposed antenna can be implemented by applying a single voltage to graphene sheets. As a result, the antenna beam direction can be readily changed by varying the applied voltage.
arXiv (Cornell University), Sep 14, 2020
In this paper, a broadband tunable polarization converter based on graphene metasurfaces is propo... more In this paper, a broadband tunable polarization converter based on graphene metasurfaces is proposed. This polarization converter works in the terahertz (THz) frequency region, using the advantage of graphene characteristics to have a tunable frequency response. The designed graphene-shaped periodic structure on top of the substrate is utilized to convert the incident wave polarization to the desired target in a flexible operational band in the THz frequencies. The polarization conversion ratio is more than 0.85 in a wide range of frequencies in the THz band from 4.86 to 8.42 THz (the fractional bandwidth is 54%). The proposed polarization converter is insensitive to the angle of the incident wave up to 40°. Using graphene provides a tunable frequency response without changing the geometry of the designed structure.
arXiv (Cornell University), Jan 6, 2021
Monitoring and controlling the state of polarization of electromagnetic waves is of significant i... more Monitoring and controlling the state of polarization of electromagnetic waves is of significant interest for various basic and practical applications such as linear position sensing and medical imaging. Here, we propose the first conformal digital metamaterial absorber to detect the polarization state of THz incident waves. The proposed polarimeter is capable of characterizing four independent polarization states of (TE, TM, ±45 • linear, and RCP/LCP) by observing the reflectivity of the structure with respect to the x-and y-direction. Besides, the proposed structure displays a strong absorptivity above 90% up to the incidence angle of 50 • for oblique incident waves with different polarizations. By mere changing the bias voltage of two orthogonal VO2 microwires via two independent computer-programmed multichannel DC network, distinct conditions for reflected waves occurs under excitations of different polarizations, whereby the polarization state of the incident wave may readily be estimated. We believe that the proposed metasurface-based polarimeter can pave the way for polarization detection applications on curved surfaces.
arXiv (Cornell University), Apr 19, 2021
For the first time, we present the design and demonstration of holographic transmitarray antennas... more For the first time, we present the design and demonstration of holographic transmitarray antennas (TAs) based on the susceptance (reactance) distribution in this paper. According to the holographic theory, the amplitudes and phases of electromagnetic waves can be recorded on a surface, and then they can be reconstructed independently. This concept is used to design single-beam and multibeam linearly polarized holographic TAs without using any time-consuming optimization algorithms. Initially, an impedance surface is analyzed for both transmission and reflection modes. As there are differences between the susceptance (reactance) distribution of these modes, a new approach (different from reflectarray designs) is proposed to apply the holographic technique to transmitarray designs. Then, interferograms are described based on the scalar transmission susceptance distribution according to the number and direction of the radiation beams. Subsequently, a transmission metasurface of dimensions equal to 0.26 0 is hired to design holographic TAs at 12 GHz. Several holograms are designed using the unit cell to verify the proposed method. Finally, as a proof of concept, a linearly polarized circular aperture wideband holographic transmitarray antenna with a radius of 13.3 cm is manufactured and tested. The antenna achieves 12.5% (11.4-12.9 GHz) 1-dB gain bandwidth and 23.8 dB maximum gain, leading to 21.46% aperture efficiency. Furthermore, the antenna achieves 95.94% simulated radiation efficiency mainly due to using subwavelength elements, which becomes possible by applying the holographic technique.
Scientific Reports
A miniaturized V-band leaky-wave antenna (LWA) with circular polarization and backward-broadside-... more A miniaturized V-band leaky-wave antenna (LWA) with circular polarization and backward-broadside-forward radiation based on a modified half-mode substrate integrated waveguide (M-HMSIW) is presented. The proposed M-HMSIW structure employs broadside coupled complementary split ring resonators to replace metallic vias, resulting in low-cost and fully-planar fabrication advantages over conventional HMSIWs. Each unit cell of the proposed LWA consists of an M-HMSIW in combination with two horizontal stubs and a cross-shaped complementary electric LC slot to provide a proper circular polarization with a composite right/left-handed property. Using this structure, the balanced condition can be obtained for the unit cell; hence a continuous backward-to-forward scanning, including broadside, is achieved. As a result, the proposed LWA with a radiator length of only 3.8 λ0 provides wide-angle beam scanning from − 53° to + 54° over the frequency range of 61.2 GHz to 73.4 GHz, while maintaining a...
2- Dimensional Beam Scanning using Reflector-Based Holographic Antenna Arrays
2022 52nd European Microwave Conference (EuMC)
Design of Wide-Band 2-D Holographic Antenna Using Wedge Reflector
2018 48th European Microwave Conference (EuMC), 2018
In this paper, the effect of forward and backward radiation modes in 2-D holographic leaky wave a... more In this paper, the effect of forward and backward radiation modes in 2-D holographic leaky wave antennas are described. The suppression of backward radiation mode is proposed to prevent the destructive effect of the excitation of the forward and backward radiation modes at frequencies that are lower than the designed operating frequency. Wedge reflector is placed next to the launcher in order to improve the radiation characteristics of the antenna. The presence of the wedge reflector changes the distribution form of the reference wave. The antenna is designed to operate over 13–18 GHz frequency band and a bandwidth of 32% is obtained.
Implementation of Parasitic DRA Elements for Improvement of Circular Polarization
IEEE Antennas and Wireless Propagation Letters, 2021
Design of Wide-band Dual-beam Leaky-wave Antenna using the Holographic Theory
2019 27th Iranian Conference on Electrical Engineering (ICEE), 2019
This paper presents a design procedure for a wideband leaky wave antenna using the holography con... more This paper presents a design procedure for a wideband leaky wave antenna using the holography concept. The artificial surface impedance formed by hexagonal metallic patches patterns the effective impedance by variations of the size of hexagonal patches. The wide-band monopole launcher is utilized to produce TM0 surface mode. Its wave function can be approximated by the Hankel function of the second kind. Two different types of planar holographic antenna designs are described. One has a single tilted main-lobe at the angle of 60 degrees, and the other has a dual-beam pattern towards symmetric directions with respect to the Z axis. Its achieved bandwidth is 40%. The beam scanning range is from 22 to 60 degrees. Simulations have been carried out by CST Microwave Studio and Ansys HFSS to verify the results.
Wide-band conversion of donut-shaped pattern to directive one by square-shaped pattern director antenna
International Journal of Microwave and Wireless Technologies, 2021
In this paper, an antenna with 8 GHz (7–15 GHz) bandwidth is designed, simulated, fabricated, and... more In this paper, an antenna with 8 GHz (7–15 GHz) bandwidth is designed, simulated, fabricated, and measured. Commonly, for the effective use of electromagnetic sources, mode converters are used to transform donut-shaped patterns to directive patterns. This paper introduces a novel antenna called the pattern director antenna (PDA) that solves most problems associated with the azimuthally symmetric output modes of high-power microwave sources. The PDA accepts directly (without the need for mode conversion) an azimuthally symmetric generated mode of an electromagnetic source and converts it to radiate a directive pattern. For the proof of concept and validation of the design by simulations, the 3D printing technology [using polylactic acid (PLA)] is used to fabricate the PDA and measure its radiation patterns and return loss. The selected material is cheap and also environmentally friendly. The antenna was coated with aluminum to become a conductor. The gain is from 16.8 to 21.8 dB in t...
Efficient $2\times2$ Printed Circuit Band-Gap Cavity-Backed Slot Antenna
IEEE Transactions on Antennas and Propagation, 2019
In this article, a novel structure is proposed for the realization of cavity section in the print... more In this article, a novel structure is proposed for the realization of cavity section in the printed gap waveguide (PGW) technology. For the proof of the concept, a multilayer cavity-backed slot antenna element is designed and fabricated so that its performance can be compared to the devices in the literature made by printed circuit board (PCB) technology and also by metal parts using the CNC machine. The proposed structure benefits from the advantages of efficient, low cost, simplified fabrication process, lightweight, and high aperture efficiency compared to common cavity-backed antennas. To manage the available space, the feed is connected to the antenna cavity from the underneath using a coupling aperture. The proposed configuration simplifies the integration of accessory devices in antenna arrays, such as feed networks, phase shifters, and amplifiers. Also, the separation of feed network from the radiation slot section prevents any unwanted radiation. Using the mode analysis, four slots were implemented in the proposed cavity to achieve four equivalent magnetic surface currents with identical phase and magnitude. The antenna operating frequency is 16 GHz, the realized antenna radiation and aperture efficiencies are over 92% and 81.6%, respectively, and its achieved gain is 12 dBi.
IEEE Transactions on Antennas and Propagation, 2019
In this paper, a novel on-glass antenna which is transparent, miniaturized and multiband is prese... more In this paper, a novel on-glass antenna which is transparent, miniaturized and multiband is presented. First of all, the antenna achieves more than 80% transparency. This is realized by removing as much as possible the metal pattern, without compromising the operational electric current flow. Second, the antenna is electrically small, at 0.95 GHz. This is realized by choosing a proper topology for the remaining metal pattern. Third, the antenna is triple band, covering the ranges 0.88-1.03 GHz, 1.47-2.74 GHz and 3.32-5.97 GHz, respectively. The radiation is omnidirectional in all bands, which is suitable for GSM900/1800, 3G, 4G, 5G (2.55-2.65 GHz), WLAN (2.4/5.2/5.8 GHz), and WiMAX (2.5/5.5 GHz). The maximum gain in the three bands is equal to-0.18 dBi, 3.66 dBi and 4.35 dBi with corresponding radiation efficiencies of 66%, 87% and 88%, respectively. A prototype is made by first printing a metallic circuit on a thin FR-4 substrate and then gluing it on a glass substrate. Measurement results are in good agreement with simulations.
Microstrip reflectarray antennas for use in satellite communications
Twelfth International Conference on Antennas and Propagation (ICAP 2003), 2003
The reflectarray antenna is an n×n microstrip patch element planar array, which reflects the inci... more The reflectarray antenna is an n×n microstrip patch element planar array, which reflects the incident fields radiating from a feed antenna. Each patch element introduces a phase change to the scattered fields. In this paper, at first it is determined the phases, which should be created by patches for radiation in a desired direction. These phases are implemented by varying both the size of patches and the length of attached stubs. Finally, the shapes of open-ended microstrip stubs are optimized to improve the bandwidth characteristics of antenna.
A novel miniaturized multilayer E-shaped patch antenna using Giuseppe Peano fractal geometry on its edges for WLAN dual-band applications
2013 21st Iranian Conference on Electrical Engineering (ICEE), 2013
The objective of this paper is to design a miniaturized two-band antenna for WLAN applications. F... more The objective of this paper is to design a miniaturized two-band antenna for WLAN applications. First, a folded square patch antenna is designed for the generation of an omnidirectional pattern. Then, two slots with their edges shaped into the Giuseppe Peano fractal geometry are engraved to form E-shaped patches. The structure is optimized to improve its bandwidth. The antenna size is miniaturized by 30% relative to an E-shaped folded antenna. A prototype model of the proposed antenna is fabricated and measured, which verifies its advantageous characteristics.
Wireless Personal Communications, 2007
In this paper the rotating angle parabolic equation method (PEM) is presented for the solution of... more In this paper the rotating angle parabolic equation method (PEM) is presented for the solution of scattering problems. Separate spectral domains for the incident and scattered fields are obtained and their sum is substituted into the wave equation. Considering the satisfaction of wave equation by the incident and scattered fields, the solution of wave equation changes into the solution of two separate parabolic equations for the incident and scattered fields. The paper continues with the development of an algorithm for the determination of back scattered fields from knife edges and scattered fields from the slope and slope discontinuities. It will be seen that the results of the proposed algorithm agree with those of other methods for the solution of aforementioned problems.
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Papers by Homayoon Oraizi