Waveguide Slot Array Antenna with a Hybrid-Phase Feed for Grating Lobe Reduction

The design of a 112-element millimeter-wave waveguide slot array antenna to reduce the grating lobe level is presented. A hybrid-phase feeding technique combining a cophase feed and an alternating-phase feed is applied to facilitate the suppression of grating lobes. In addition, a stepped feed waveguide and offset coupling slots aligned in a line are employed to realize a tapered aperture distribution. As a result, grating lobe suppression of 8.1 dB was achieved on the diagonal planes compared to a conventional alternating-phase-fed waveguide slot array antenna. A prototype of the proposed antenna was fabricated and measured. The measured results show that the proposed antenna exhibits a −15 dB reflection bandwidth of 3.4% and an average realized gain of 26.72 dBi within the measured frequency range. Good agreement between the simulated and measured radiation patterns is also observed

Understanding the formation of the metastable ferroelectric phase in hafnia–zirconia solid solution thin films

Hf₁₋ₓZrₓO₂ (x ∼ 0.5–0.7) has been the leading candidate of ferroelectric materials with a fluorite crystal structure showing highly promising compatibility with complementary metal oxide semiconductor devices. Despite the notable improvement in device performance and processing techniques, the origin of its ferroelectric crystalline phase (space group: Pca2₁) formation has not been clearly elucidated. Several recent experimental and theoretical studies evidently showed that the interface and grain boundary energies of the higher symmetry phases (orthorhombic and tetragonal) contribute to the stabilization of the metastable non-centrosymmetric orthorhombic phase or tetragonal phase. However, there was a clear quantitative discrepancy between the theoretical expectation and experiment results, suggesting that the thermodynamic model may not provide the full explanation. This work, therefore, focuses on the phase transition kinetics during the cooling step after the crystallization annealing. It was found that the large activation barrier for the transition from the tetragonal/orthorhombic to the monoclinic phase, which is the stable phase at room temperature, suppresses the phase transition, and thus, plays a critical role in the emergence of ferroelectricity

Paricalcitol Pretreatment Attenuates Renal Ischemia-Reperfusion Injury via Prostaglandin E 2

The protective mechanism of paricalcitol remains unclear in renal ischemia-reperfusion (IR) injury. We investigated the renoprotective effects of paricalcitol in IR injury through the prostaglandin E2 (PGE2) receptor EP4. Paricalcitol was injected into IR-exposed HK-2 cells and mice subjected to bilateral kidney ischemia for 23 min and reperfusion for 24 hr. Paricalcitol prevented IR-induced cell death and EP4 antagonist cotreatment offset these protective effects. Paricalcitol increased phosphorylation of Akt and cyclic AMP responsive element binding protein (CREB) and suppressed nuclear factor-κB (NF-κB) in IR-exposed cells and cotreatment of EP4 antagonist or EP4 small interfering RNA blunted these signals. In vivo studies showed that paricalcitol improved renal dysfunction and tubular necrosis after IR injury and cotreatment with EP4 antagonist inhibited the protective effects of paricalcitol. Phosphorylation of Akt was increased and nuclear translocation of p65 NF-κB was decreased in paricalcitol-treated mice with IR injury, which was reversed by EP4 blockade. Paricalcitol decreased oxidative stress and apoptosis in renal IR injury. Paricalcitol also attenuated the infiltration of inflammatory cells and production of proinflammatory cytokines after IR injury. EP4 antagonist abolished these antioxidant, anti-inflammatory, and antiapoptotic effects. The EP4 plays a pivotal role in the protective effects of paricalcitol in renal IR injury

A Comparative Study on the Ferroelectric Performances in Atomic Layer Deposited Hf0.5Zr0.5O2 Thin Films Using Tetrakis(ethylmethylamino) and Tetrakis(dimethylamino) Precursors

Abstract The chemical, physical, and electrical properties of the atomic layer deposited Hf0.5Zr0.5O2 thin films using tetrakis(ethylmethylamino) (TEMA) and tetrakis(dimethylamino) (TDMA) precursors are compared. The ligand of the metal-organic precursors strongly affects the residual C concentration, grain size, and the resulting ferroelectric properties. Depositing Hf0.5Zr0.5O2 films with the TDMA precursors results in lower C concentration and slightly larger grain size. These findings are beneficial to grow more ferroelectric-phase-dominant film, which mitigates its wake-up effect. From the wake-up test of the TDMA-Hf0.5Zr0.5O2 film with a 2.8 MV/cm cycling field, the adverse wake-up effect was well suppressed up to 105 cycles, with a reasonably high double remanent polarization value of ~40 μC/cm2. The film also showed reliable switching up to 109 cycles with the 2.5MV/cm cycling field without involving the wake-up effect but with the typical fatigue behavior

Low-Profile Spidron Fractal Dipole Antenna with a Ferrite-Loaded Artificial Magnetic Conductor for Manpack Applications

In this paper, a Spidron fractal dipole antenna with a ferrite-loaded artificial magnetic conductor (AMC) is presented. By applying ferrite composed of nickel–zinc with a high permeability value, a compact AMC that operates in the broadband frequency range within the high-frequency/very-high-frequency/ultra-high-frequency (HF/VHF/UHF) bands was designed. A Spidron fractal-shaped dipole antenna with a quasi-self-complementary structure was designed and combined with a miniaturized ferrite-loaded AMC. This allowed the designed AMC-integrated dipole antenna to operate in a wide frequency band, covering the HF/VHF/UHF bands, with low-profile characteristics. A prototype of the proposed Spidron fractal dipole antenna with the AMC was manufactured and measured and found to meet low VSWR (voltage standing wave radios) specifications of <3.5 within the 20–500 MHz bandwidth range. The simulated and measured results are in good agreement. The size of the Spidron fractal dipole antenna with the AMC is 0.03×0.026×0.001λ3 relative to the wavelength of the lowest operating frequency. The received power of the Spidron fractal dipole antenna with the AMC was also measured when it was applied to relatively small applications, such as a manpack in this case

Design of a Wide-Beamwidth Pixelated Dielectric Resonator Antenna Using a Modified Stepped-Impedance Filter to Suppress Harmonics

This study designed a wide-beamwidth pixelated dielectric resonator antenna (DRA) combined with a low-pass filter (LPF) to suppress harmonics. The DRA was designed to create a wide-beam pattern with a pixelated structure. The pixelated DRA was optimized by a genetic-learning particle swarm optimization algorithm. To prevent significant higher-mode radiation and harmonics from occurring in the DRA, an LPF was included in its feeding line. The filter had a seventh-order Chebyshev design, and a hybrid step-impedance filter was proposed by modifying the step-impedance filter for use in narrow spaces behind the ground

Ferrite-Loaded Spidron Fractal Loop VHF Antenna for UAV Applications

In this letter, an electrically small Spidron fractal loop antenna operating in the VHF band is proposed. The ferrite material, which consists of a nickel-zinc combination, is loaded into inside of the loop antenna to increase the gain of the antenna in the low frequency band. To minimize the magnetic loss of the ferrite in the high frequency band, the amount and configuration of the ferrite are optimized using a genetic algorithm. Through this optimization step, the amount of the ferrite is decreased to 37.5% and the gain of the antenna in the high frequency band is improved. The size of the proposed antenna is 0.0242 × 0.0242 × 0.0051 λL3 at the lowest operating frequency. The proposed antenna was fabricated to verify the performance, and the simulated and measured results are in good agreement. The measured peak gains varied from −31.6 to −1.9 dBi within the measured frequency band. To examine the performance of the proposed antenna mounted on an unmanned aerial vehicle model (UAV), the antenna on a UAV was also simulated and the results were discussed. The simulated realized peak gains of the antenna on the UAV and on flat ground are similar