Microwave and Optical Technology Letters最新文献

The present study introduces a low-profile beam-steering metasurface lens antenna (MLA) that is excited by a defocused array antenna (DAA), eliminating the need for amplitude and phase excitation modulation. First, we modify an ultrathin Huygens' unit cell to provide greater angular stability, which is intended for use in beam-steering lens antennas. Subsequently, we analyze the effect of the focal–diameter ratio (F/D) on the beam-steering performance of the lens. Further, a one-dimensional (1D) MLA equipped with a DAA is modeled. Based on this model, we investigate the influence of DAA distance from the lens, DAA diameter, and F/D on radiation directivity and scanning capability. By adjusting the distance between the DAA and the lens, sub-arrays located in different regions of the DAA can be excited with uniform amplitude and phase, enabling dual-polarized single-beam scanning radiation. This excitation technique eliminates the need for amplitude and phase modulation networks, thereby reducing beam-steering costs and the complexity of the feed network. Finally, a 10$��\; ��{\lambda }_0�\; �\times ��$10$��\; ��{\lambda }_0��$ MLA prototype excited by a 52-unit dual-polarized DAA is simulated and fabricated. The simulation and measurement results demonstrate that the proposed MLA achieves a scanning range of ± 15°/± 16° in the E/H-plane at 10.3 GHz, with a gain fluctuation of less than 2.35/2.25 dB.

A low-insertion-loss, high-power rectangular waveguide-to-coaxial transition is proposed in this letter. The proposed rectangular waveguide-to-coaxial transition is constructed by a rectangular-waveguide H–T junction and square coaxes. The H-plane T-junction is used to convert the input wave into two in-phase waves. After passing through three 90° bends, the electric field vectors of the two in-phase waves are in opposite directions. Then they combine at the coaxial port. The TE10 mode in the rectangular waveguide is converted to the TEM mode in the coaxial line by the transition ridge. The power capacity of the transition is increased by the N-type connector. For verification, an X-band rectangular waveguide-to-coaxial transition has been designed, fabricated, and measured. The measured results show that the 20-dB fractional bandwidth is 22.4%. The insertion loss is no more than 0.1 dB. The transmission efficiency is 97.7%. And the power capacity can reach 65 kW.

This paper proposes a nonreciprocal array antenna based on spatiotemporal modulation. This approach relies on the drastically different phase response during the frequency conversion processes in the time-modulated antenna element. A prototype linear array composed of a pair of resonant patches is designed and fabricated for proof-of-concept validation. Measured results are in good agreement with simulation. The results show that the proposed array antenna is capable of providing versatile radiation performance for transmission and reception, including reciprocal transmission and reception radiation beams, nonreciprocal symmetric transmission and reception radiation beams, and nonreciprocal asymmetric transmission and reception radiation beams, by manipulating the RF signal phase and modulation signal phase.

This article introduces a compact non-planner inverted stacked microstrip antenna tailored for ultrawideband (UWB) applications. The innovative design of the antenna features a folded feed technique combined with a slotted lower patch and an additional parasitic upper patch, showcasing a novel approach to enhancing performance. Compactness is achieved by integrating a shorting wall, significantly reducing the antenna size without compromising performance. The proposed antenna demonstrates exceptional simulated bandwidth (S11<−10 dB) of 11020 MHz (3.6–14.62 GHz), equivalent to 120.9%, and measured impedance bandwidth of 11310 MHz (3.63–14.94 GHz), reflecting a substantial fractional bandwidth of 121.80%. Furthermore, it achieves a peak gain of 9 dBi, making it highly suitable for UWB operations. The combination of its compact size, extensive bandwidth, and stable radiation patterns makes this antenna a highly effective and appropriate choice for UWB technology.

This letter presents a novel wideband high gain and low radar cross section reduction (RCS) Fabry–Perot (FP) antenna using a single layer partially reflective surface (PRS). Different from the traditional PRS unit, the proposed PRS unit can broaden the gain bandwidth and reduce the in-band RCS. The designed PRS distributes the radiated waves in-phase through the positive phase gradient compensation and weakens the reflection of the incident waves through the phase cancellation. Compared to the previous wideband low RCS FP antennas, we first achieved the 3 dB gain bandwidth covering the 10 dB impedance bandwidth. Both the simulation and measured results verify the performance of the proposed FP antenna. The results show that the proposed FP antenna has a 10 dB impedance bandwidth of 8.6–11.8 GHz (31.4%) and an RCS reduction bandwidth of 7.9–14.0 GHz (55.7%) under the normal incidence. The 3 dB gain bandwidth and the maximum realized gain are 8.3–12.0 GHz (36.5%) and 16.3 dBi.

A high-quality (Q) low-noise amplifier (LNA) combined with a voltage-controlled oscillator (VCO) is presented for small frequency errors in self-calibration. The proposed new double capacitive-cross-coupled structure controls negative impedance and thus, changes the working mode between the LNA and VCO with a small variation of parasitic capacitance, which results in a small calibration frequency error. High-Q and low-noise performances were theoretically analyzed and confirmed by simulation and measurement. The measured LNA operated from 2.2 to 2.44 GHz with a Q-factor of 34 while the frequency offset was less than 0.9%. A power gain of 27 dB, noise figure of 2.1 dB, and input third-order intercept point (IIP3) of −17 dBm were obtained while the power dissipations of the LNA and VCO modes were 10.2 and 4.7 mW from a 1.5-V supply, respectively.

Stable and periodic soliton molecules (SMs) have been studied numerically by coupled nonlinear Schrodinger equations (CNLSEs). Split and formation processes of different-order SMs are observed by changing saturation power and filtering bandwidth. Bimodal pulses of SMs are in a transition state toward higher-order SMs. Short-period and long-period SMs are observed by adjusting saturation power. The research contributes to revealing SM dynamics, which has potential applications in encoding as well as optical storage.

The generation of high-coherence mid-infrared (MIR) supercontinuum (SC) spanning over one octave in As₂Se₃ tapered photonic crystal fiber (As₂Se₃-TPCF) is investigated through numerical simulations. Combined with the photonic crystal fiber and tapered fiber's structural characteristics, six As₂Se₃-TPCFs with different tapered structures are designed. The tapered regions are the power function and cosine tapered structures, respectively, while the taper waist and the untapered region have the same structure. Moreover, the nonlinear coefficient of the taper waist is 2.23825 W⁻¹m⁻¹ calculated by the finite element method (FEM), and the zero-dispersion wavelength (ZDW) in the down-taper moves with the increase of transmission distance, shifted from 5.2 to 2.4 μm. The temporal and spectral features of the MIR SC generated in As₂Se₃-TPCFs are numerically simulated by solving the generalized nonlinear Schrödinger equation (GNLSE), and the spectral broadening of As₂Se₃-TPCFs is mainly caused by self-phase modulation, Raman soliton self-frequency shift, and dispersive wave generation. Finally, six As₂Se₃-TPCFs with lengths of 0.1 m are pumped by short pulses with a center wavelength of 4.0 μm, pulse width of 40 fs, and pulse energy of 250 pJ, the results show that the linear tapered As₂Se₃-TPCF and the cosine tapered As₂Se₃-TPCF can achieve high-coherence MIR spectra spanning 1.6 octaves, with spectral widths from 2.1 to 6.4 μm.