Search Results (32)

This article presents a novel, compact, and flexible dual-band magnetoelectric dipole rectenna designed for radio frequency (RF) energy harvesting. The rectenna consists of a unique antenna structure, combining electric and magnetic dipoles to create unidirectional radiation patterns, minimizing interference from the human body. The rectifier is integrated with the antenna through conjugate matching, eliminating the need for additional matching circuits, reducing circuit losses, minimizing design complexity, and improving conversion efficiency. The proposed rectenna utilizes a flexible graphene film as the radiating element, which offers excellent conductivity and corrosion resistance, enabling conformal operation in diverse scenarios. Simulation and experimental results show that the rectenna operates effectively at 3.5 GHz and 4.9 GHz, achieving peak conversion efficiencies of 53.43% and 43.95%, respectively, at an input power of 4 dBm. The simulated and measured results achieved good agreement. The rectenna maintains stable performance under various bending conditions, demonstrating its suitability for flexible, wearable RF energy-harvesting systems. Full article

This paper presents a D-band dual linear-polarized wideband high-gain reflectarray (RA) antenna using low-temperature co-fired-ceramic (LTCC) technology. The proposed element comprises a dual-polarized magnetoelectric (ME) dipole and a multilayer slot-coupling substrate-integrated waveguide (SIW) phase-delay structure, which are organized in accordance with the receiving/reradiating (R/R) principle. The coverage of phase shifts for both orthogonal polarizations is set to be greater than 360 degrees by varying the length of the phase-delay structure. For verification, a D-band 1296-element RA prototype using the proposed unit cell is fabricated and measured in a THz chamber. The measured results show that the proposed RA achieves a peak gain of 32.25 and 33.03 dBi for the two orthogonal polarizations. The measured 3 dB gain bandwidths for the two orthogonal polarizations are 122–149 GHz (20%) and 123–149 GHz (19.3%), respectively. Full article

This study presents a novel methodology for designing a planar broadband wide-scanning dual-polarized array using tightly-coupled dipoles and wide-angle impedance matching. By etching the S-shaped gaps between the dipoles and incorporating shorting vias with defected ground structures, we demonstrated that all radiation elements can be arranged on a single-layer substrate. Additionally, we introduced a thin printed circuit board (PCB) layer with two-dimensional periodic structures for impedance matching at wide scan angles. Leveraging high permittivity and constrained electromagnetic waves, we realized zero-scan blindness within this band. The aperture consisted of only two PCB layers, with a total profile of approximately 0.091λ_low, where λ_low represented the free-space wavelength at 6 GHz. A 3 × 4 dual-polarized array was fabricated and measured to validate the proposed approach. The measured active voltage standing wave ratio for one embedded array element surpassed 2.2 over 6–18 GHz. By enabling the orthogonal dipoles at the edge of the array to be mutually coupled using an additional metal patch, the active S₁₁ for the edge cells exceeded −8.8 dB over 6.9–18 GHz. The measured patterns were in good agreement with simulations over 6–18 GHz, with the array exhibiting good radiation performance over ±60° in the E- and H-planes. Full article

This paper presents a wideband dual-polarized dipole antenna structure operating at 1.7–3.8 GHz (76.4%). For a traditional 4G dipole antenna that covers the band 1.71–2.69 GHz, it is difficult to maintain the satisfactory impedance matching and normal stable radiation patterns within the 5G sub-6 GHz band 3.3–3.8 GHz, mainly due to the fixed antenna height no longer being a quarter-wavelength. To solve this, a connected-ring-shaped metasurface structure is proposed and deployed to operate as an artificial magnetic conductor (AMC). As a result, stable antenna radiation patterns are obtained within the whole band 1.7–3.8 GHz. For verification, this wideband dipole antenna using AMC is implemented and tested. The measured results show that the proposed antenna has an impedance bandwidth of 80.7% (1.7–4.0 GHz). It has an average measured in-band realized gain of $7.0\pm 1.0$ dBi and a stable $70\pm 5$ half power beam width (HPBW) within the 4G/5G-sub 6GHz bands 1.71–2.69 GHz and 3.3–3.8 GHz. Full article

A broadband dual-polarized crossed dipole antenna is proposed in this paper. To achieve a wide impedance bandwidth and low-profile configuration, a novel bow-tie balun is applied to this antenna. Firstly, the working mechanisms of both bow-tie baluns and the antenna are introduced. Then, the parametric study and design guidelines are presented. Finally, the optimized antenna is fabricated, measured, and analyzed. The simulated and measured results show that the antenna has a wide impedance bandwidth from 2.42 GHz to 6.48 GHz. The fractional bandwidth is 91.2%. Moreover, within the whole band, the E-plane and H-plane radiation patterns are stable. The port isolation is greater than 20 dB, and the cross-polarization discrimination ratio is better than 25 dB. The proposed antenna achieves a realized gain of $7.5 \mathrm{d}\mathrm{B}\mathrm{i} \pm 0.5 \mathrm{d}\mathrm{B}\mathrm{i}$. It can be a good candidate for sub-6 GHz wireless communications or short-range radar applications. Full article

In this study, the spherical particle model and ten nonspherical particle models describing the scattering properties of snow are evaluated for potential use in precipitation estimation from spaceborne dual-frequency precipitation radar. The single scattering properties of nonspherical snow particles are computed using discrete dipole approximation (DDA), while those of spherical particles are determined using Mie theory. The precipitation profiles from WRF output are then input to a forward radiative transfer model to simulate the radar reflectivity at Ka-band and Ku-band. The results are validated with Global Precipitation Mission Dual-Frequency Precipitation Radar measurements. Greater consistency between the simulated and observed reflectivity is obtained when using the sector- and dendrite-shape assumptions. For the case in this study, when using the spherical-shape assumption, radar underestimates the error of the cloud’s top by about 300 m and underestimates the error of the cloud’s area by about 15%. As snowflake shapes change with temperature, we use the range between −40 °C and −5 °C to define three temperature layers. The relationships between reflectivity (Z) and precipitation rate (R) are fitted separately for the three layers, resulting in $\mathrm{Z}=134.59·{\mathrm{R}}^{1.184}$ (sector) and $\mathrm{Z}=127.35·{\mathrm{R}}^{1.221}$ (dendrite) below −40 °C. Full article

In this study, a dual-polarization and low-profile frequency-selective rasorber (FSR) constructed from a novel band-patterned octagonal ring and dipole slot-type elements is investigated. We show the process of designing from a full octagonal ring to realize a lossy frequency selective surface of our proposed FSR, and it has a passband with low insertion loss between the two absorptive bands. An equivalent circuit for our designed FSR is modeled to explain the introduction of the parallel resonance. Surface current, electric energy, and magnetic energy of the FSR are further investigated to illustrate the working mechanism. Simulated results indicate that S₁₁ < −10 dB bandwidth within 5.2–14.8 GHz, S₂₁ > −3 dB passband within 9.62–11.72 GHz, lower absorptive bandwidth within 5.02–8.80 GHz, and upper absorptive bandwidth within 12.94–14.89 GHz are obtained under normal incidence. Meanwhile, our proposed FSR possesses the properties of dual-polarization and angular stability. To verify the simulated results, a sample with thickness of 0.097 λ_L is manufactured, and the results are experimentally verified. Full article

This study presents a novel dual-polarized magnetoelectric dipole antenna and its array with director and rectangular parasitic metal patches for LTE and 5G sub-6 GHz base station applications. This antenna is composed of L-shaped magnetic dipoles, planar electric dipoles, rectangular director, rectangular parasitic metal patches, and η-shaped feed probes. The gain and bandwidth were enhanced by using the director and parasitic metal patches. The measured impedance bandwidth of the antenna was 82.8% (1.62–3.91 GHz, VSWR < 1.5), and its gain was 10 ± 0.5 dBi. The profile of the antenna unit, operated at 1.7 GHz, was only 42 mm (0.227λ₀, where λ₀ represents the free space wavelength corresponding to the lowest resonance frequency point). Subsequently, four antenna units were arranged in a line array with 0.6λ₀ spacing. Both the antenna and its array were fabricated and measured. The measurement results show that the array has good radiation characteristics, such as broad bandwidth covering 1.65–3.97 GHz (VSWR < 1.5), high gain (its gain was great than 15.2 dBi), and high radiation efficiency (>90%). Its HPBWs were 63° ± 4° and 15° ± 2° for H- and E-planes, respectively. The design can cover TD-LTE and 5G sub-6 GHz NR n78 frequency bands very well, meaning that this is a good candidate antenna for base station applications. Full article

A low-profile dual-polarized magneto-electric dipole (MED) is presented in this communication. The low profile was achieved using meander slots on the vertical magneto dipole, reducing the antenna height to 0.15λ₀, where λ₀ is the wavelength of the center frequency. Relatively, the proposed MED structure is easier to process and more stable than the traditional low-profile MED structure. The broadband performance for 5G Applications was realized based on MED structure, and the dual-polarization structure has wider coverage area and lower multipath transmission losses. Moreover, the orthogonal feeding structure provides a satisfying isolation between two ports. To verify the simulation results, a prototype of the proposed antenna was fabricated and measured. The results show that the overlapped operating frequency bandwidth with |S11| ≤ −10 dB, |S12| ≤ −20 dB was 36.8% from 3.1 GHz to 4.5 GHz, the peak gain reached 10.2 dBi, and the average gain exceeded 8.5 dBi. The measured 3 dB beamwidth with more than 44 degrees beamwidth was realized in both E-plane and H-plane. In addition, cross-polarization levels below −22 dB that covered the above frequency band were achieved. Compared with other MED antennas, in addition to broadband and high gain, the proposed antenna has the advantages of a low profile, easy processing, and low cost, which make it a competitive candidate for 5G applications. Full article

This paper proposes a dual-polarization dipole antenna for a cylindrical phased array working in Ku-band. The dipole antenna is double-layer structured and is composed of two orthogonal butterfly shaped dipole radiators, two ground co-planar waveguide (GCPW) feeding structures and vias. Each dipole is in the shape of a butterfly. The dipole patch is grooved triangularly and one side of it is bent into an N shape, which effectively expands the working frequency band of the antenna. The double-layer structure improves the isolation between the antenna ports. The antenna works between 15 GHz to 16.2 GHz and the isolation between the antenna’s two feeding ports in this band is better than 20 dB. The proposed dipole antenna is applied in a 32-element cylinder array. The simulation and measured results show that the array can scan between −60° to +60° in the azimuth plane with a gain fluctuation less than 2.5 dB. Therefore, the proposed design is an attractive candidate for conformal devices at Ku-band frequencies, and it also has a great potential for application in larger antenna arrays. Full article

A low-profile planar millimeter-wave (MMW) folded dipole antenna fed by substrate integrated waveguide (SIW) is proposed in this letter. By etching the gaps at the proper position of 1.5λ dipole, an additional resonant mode is generated. Accordingly, the working bandwidth is greatly broadened. In addition, by appropriately adjusting the length of the dual-side parallel strip line (DSPSL), the radiated electric fields generated by the aperture of the feeding SIW and the connecting metallic vias of the folded dipole are designed with an out-of-phase potential. Hence, the cross-polarization of the presented folded dipole antenna is improved as well. As a demonstration, a prototype is fabricated and measured. The experimental results exhibit that the proposed folded dipole has a −10 dB impedance bandwidth of 58.5% (from 30.3 GHz to 53.7 GHz), a gain of around 5 dBi with more than 120 degrees beamwidth in H-plane, and a cross-polarization levels below −15 dB, covering the working frequency band. Compared with the up-to-date planar dipole antenna, the proposed folded dipole achieves the widest working bandwidth and low cross-polarization level. The proposed antenna can be used as the terminal antenna of the MMW communication system. Full article

In this paper, a low-loss toroidal dipole metamaterial composed of four metal split ring resonators is proposed and verified at microwave range. Dual-band Fano resonances could be excited by normal incident electromagnetic waves at 6 GHz and 7.23 GHz. Analysis of the current distribution at the resonance frequency and the scattered power of multipoles shows that both Fano resonances derive from the predominant novel toroidal dipole. The simulation results exhibit that the sensitivity to refractive index of the analyte is 1.56 GHz/RIU and 1.8 GHz/RIU. Meanwhile, the group delay at two Fano peaks can reach to 11.38 ns and 12.85 ns, which means the presented toroidal metamaterial has significant slow light effects. The proposed dual-band toroidal dipole metamaterial may offer a new path for designing ultra-sensitive sensors, filters, modulators, slow light devices, and so on. Full article

Fluorescent probes that exhibit solvatochromic or excited-state proton-transfer (ESPT) properties are essential tools for the study of complex biological or chemical systems. Herein, the synthesis and characterization of a novel fluorophore that reveals both features, 5-isocyanonaphthalene-1-ol (ICOL), are reported. Various solvatochromic methods, such as Lippert–Mataga and Bilot–Kawski, together with time-dependent density functional theory (TD-DFT) and time-resolved emission spectroscopy (TRES), were applied to gain insights into its excited-state behavior. To make comparisons, the octyloxy derivative of ICOL, 5-isocyano-1-(octyloxy)naphthalene (ICON), was also prepared. We found that internal charge transfer (ICT) takes place between the isocyano and –OH groups of ICOL, and we determined the values of the dipole moments for the ground and excited states of both ICOL and ICON. Furthermore, in the emission spectra of ICOL, a second band at higher wavelengths (green emission) in solvents of higher polarities (dual emission), in addition to the band present at lower wavelengths (blue emission), were observed. The extent of this dual emission increases in the order of 2-propanol < methanol < N,N-dimethylformamide (DMF) < dimethyl sulfoxide (DMSO). The presence of the dual fluorescence of ICOL in these solvents can be ascribed to ESPT. For ICOL, we also determined ground- and excited-state pK_a values of 8.4 ± 0.3 and 0.9 ± 0.7, respectively, which indicates a considerable increase in acidity upon excitation. The TRES experiments showed that the excited-state lifetimes of the ICOL and ICON spanned from 10.1 ns to 5.0 ns and from 5.7 ns to 3.8 ns, respectively. In addition, we demonstrated that ICOL can be used as an effective indicator of not only the critical micelle concentration (cmc) of ionic (sodium lauryl sulfate (SLS)) and nonionic surfactants (Tween 80), but also other micellar parameters, such as partition coefficients, as well as to map the microenvironments in the cavities of biomacromolecules (e.g., BSA). It is also pointed out that fluorescence quenching by pyridine can effectively be utilized for the determination of the fractions of ICOL molecules that reside at the water–micelle interface and in the interior spaces of micelles. Full article

A design of a modular antenna/detector array for the electron cyclotron emission (ECE) imaging system at the Korea Superconducting Tokamak Advanced Research (KSTAR) is proposed. The modular antenna/detector array is based on a unit antenna/detector module, which consists of an elliptical mini-lens, a dual-dipole antenna, an antenna balun, a low-noise amplifier, and a metal frame. The proposed modular antenna/detector array resolves the problem in the conventional antenna/detector array where one faulty channel requires the entire array to be removed for the service. With the proposed modular array, each channel module can be easily and independently removed and replaced without interference to the rest of the array, thus minimizing the interrupted service time for maintenance. Moreover, the unit channel modules can be efficiently updated under a variety of the tokamak operation conditions. The antenna/detector modules are optimized to have improved performance, and are tested in a W-band test setup, and consistently provide the gain increase by 10~20 dB as compared with the conventional antenna/detector array. A set of the proposed modular antenna/detector array is currently installed and tested in the KSTAR ECE imaging system, and will consistently produce the improved ECE imaging to monitor MHD instability activities under various plasma operation conditions. Full article

This paper presents a novel hybrid antenna with equal beamwidth in two frequency bands for short-range radar applications. The proposed design consists of a 2 × 2 patch array and a SIW-fed dielectric rod antenna. The two kinds of radiators are responsible for the 5.8 GHz and 24 GHz ISM bands, respectively. Pencil beams are obtained in both lower and upper bands. The beamwidth generated by the dielectric rod can be flexibly tuned to coincide with that of the patch array. Magneto-electric (ME) dipole, composed of a slot and two parasitic monopoles, is constructed to replace the conventional 3-D waveguide feeder, which can excite the dielectric rod effectively. The complementary structure is helpful to obtain a pencil beam. The 2 × 2 patch array has the size of 70 × 70 mm² and is fed by a four-way power divider. Due to no overlapping radiating aperture, the two radiators can work independently with high port isolation. The measured peak gain in the two bands is 12.5 dBi and 12.7 dBi. The measured 3-dB beamwidth at 5.8 GHz and 24 GHz is 42° and 39° in x-z plane, and 43° and 42° in the y-z plane. The proposed antenna features a small beamwidth difference in two frequency bands, thus being attractive for dual-band radar systems. Full article