230 research outputs found
Triple-band planar dipole antenna for omnidirectional radiation
No full textThis Letter presents a compact triple-band dipole antenna that radiates omnidirectionally. The antenna is a T-shaped structure that is excited through a vertical feedline. Located under the horizontal rectangular patch are two λ/2 long meander-line stubs symmetrically interfaced to the feedline. On the bottom side of the substrate is a trident shaped ground-plane structure located under the T-shaped radiator. The proposed configuration is essentially composed of three radiating elements, which has a small footprint of 19×16 mm2 on a 0.8 mm thick substrate. Regions of enhanced impedance matching are realized between 0.5 – 2.69 GHz, 3.2 – 4.44 GHz and 4.82 – 6.6 GHz covering major portions of L, S and C-bands. It is shown by reducing the gap between the meander lines stub and rectangular patch reduces results in increased gain performance. Measured results confirm the antenna exhibits omnidirectional radiation with enhanced impedance match at 1.5, 4 and 5.4 GHz with corresponding average gain of 1.6 dBi, 3.4 dBi and 3 dBi, respectively
Wideband planar array antenna based on SCRLH-TL for airborne synthetic aperture radar application
No full textThis paper presents empirical results of a novel planar microstrip array antenna based on a simplified composite right/left-handed transmission line (SCRLH-TL) for application in circularly polarized synthetic aperture radar (CP-SAR) systems operated in UHF, L, S, and C-Bands. The array antenna consists of 6x6 matrix of spiral-shaped radiating elements that are excited through proximity-coupled, single feed-line. Pattern synthesis technique is used to determine the excitation coefficients (amplitude and phase) to apply to the individual array elements to achieve the required pattern shape. The array antenna has dimensions of 111.5x96.06mm(2). The measured impedance bandwidth of the antenna is 3.85GHz for S-11<-10dB from 300MHz to 4.15GHz, corresponding to a fractional bandwidth of 173%. Maximum gain and radiation efficiency measured are 4.8 dBi and 79.5%, respectively, at 2.40GHz. The antenna has a 3-dB axial-ratio bandwidth of 3.94GHz from 144MHz to 4.66GHz. The antenna's beamwidth in azimuth and elevation planes vary between 60 degrees and 120 degrees across its operational frequency range from 300MHz to 4.15GHz. The antenna design fulfills the challenging electrical and physical specifications required for CP-SAR employed onboard unmanned aerial vehicle (UAV)
Extended Aperture Miniature Antenna Based on CRLH Metamaterials for Wireless Communication Systems Operating Over UHF to C-Band
No full textThis paper presents a simple technique to extend the aperture of planar composite right/left-handed (CRLH) metamaterial antennas with minimal impact on the antenna’s dimensions. Unlike most CRLH antenna structures the proposed antenna is via-free. The proposed antenna is shown to operate over a wideband from UHF to C-band with good radiation characteristics. The antenna configuration consists of a vertically stacked CRLH unit-cells comprising of a patch and meandered lines, where the patch is engraved with an S-shaped slot. The design uses minimal ground plane area. The meander line inductance is grounded using CPW ground which eliminates conventional CRLH TL metallic via into ground plane. The antenna is feed through a coplanar waveguide (CPW) match stub that is electromagnetically coupled to the unit cells. Antenna dimensions are 17.5×32.15×1.6 mm3, which corresponds to 0.204λ_0×0.375λ_0×0.018λ_0 where free-space wavelength (λ_0) is 3.5GHz. Parametric study enabled the optimization of the antenna performance in terms of impedance bandwidth, radiation gain and radiation efficiency. Measured results confirm the antenna can operate from 850 MHz to 7.90 GHz, which is equivalent to a fractional bandwidth of 161.14%. The antenna has a maximum gain and radiation efficiency of 5.12 dBi and ~80%, respectively, at 3.5GHz
Secure satellite downlink with hybrid RIS and AI-based optimization
No full textIn this paper, we explore a secure multiuser multiple-input single-output (MISO) satellite downlink communication system, enhanced by the integration of a hybrid reconfigurable intelligent surface (RIS). The study formulates a robust joint design for satellite and RIS beamforming, aimed at maximizing the secrecy rate of the overall system. Both the active and passive elements of the RIS are optimized, taking into account practical models that reflect real-world constraints, such as outdated channel state information (CSI) and the power consumption of the system. To address the highly complex, dynamic, and multidimensional nature of the beamforming design problem, deep reinforcement learning (DRL) techniques are employed. Simulation results demonstrate the effectiveness of the proposed beamforming strategy, highlighting significant performance improvements when utilizing hybrid-RIS compared to traditional passive RIS solutions in wireless communication systems
CRLH Metamaterial Transmission Line Based-Wideband Planar Antenna for Operation Across UHF/L/S-bands
No full textThe paper presents a miniature wideband antenna using composite right/left-handed transmission-line (CRLH-TL) metamaterial. The proposed planar antenna has a fractional bandwidth of 100 percent and is designed to operate in several frequency bands from 800MHz to 2.40GHz. The antenna is constructed using just two CRLH-TL unit cells comprising of two Tshaped slots that are inverted. The slots contribute towards generating the series left-handed (LH) capacitance CL. The rectangular patch on which the slots are created is grounded with spiral shaped high impedance stubs that contribute towards LH inductance LL. The antenna has a size of 14 by 6 by 1.6 mm3 (0.037λ0 by 0.016λ0 by 0.004λ0, where λ0 is free space wavelength at 800MHz). The peak gain and efficiency of the antenna are 1.5dBi and approximately 75%, respectively, at 1.6GHz. Proposed antenna is suitable for use in wireless systems working at UHF/L/S-bands, in particular, AMPS, GSM, WCDMA, UMTS, PCS, cellular, DCS, IMT-2000, JCDMA, KPCS, GPS, lower band of WiMAX
A Novel Monofilar-Archimedean Metamaterial Inspired Leaky-Wave Antenna for Scanning Application for Passive Radar Systems
No full textA novel backfire-to-endfire leaky-wave antenna is presented with ability to scan from -25ο to +45ο. The antenna is based on metamaterial transmission-lines (MTM-TLs) and is implemented using Monofilar Archimedean spiral and rectangular slots, spiral inductors and metallic via-holes. The slots act as series left-handed capacitances, and the spirals with via-holes provide the shunt left-handed inductances to realize the metamaterial antenna. A prototype antenna was fabricated prototype on FR4 dielectric substrate, which has an electrical size of 0.0302λo×0.0357λo×0.0008λo, where λo is free space wavelength at 165 MHz. Measured bandwidth of the antenna is 710 MHz (165-875 MHz) corresponding to a fractional bandwidth of 136.5%. The main advantage of the antenna is its ability to scan over a wide angle from -25 degrees to +45 degrees with acceptable gain and radiation efficiency of 1.2 dBi and 50.1%, respectively, measured at 400 MHz. The wide scanning attributes of the antenna make it suitable for passive radar applications to scan across the VHF-UHF bands for FM-Radio, television, mobile phones and GPS applications
- …
