Microwave and Optical Technology Letters最新文献

In this paper, an all-fiber passively Q-switched (QS) Er-doped fiber laser (EDFL) was designed and successfully demonstrated by innovatively employing germanene as saturable absorber (SA). Due to its low-warp honeycomb structure and remarkable zero bandgap property, germanene exhibits excellent potential for highly stable broadband pulse modulation. Based on the saturable absorption effect of germanene, a stable passive QS laser output was successfully achieved at 1530 nm under a threshold pump power of 63.7 mW. With the pump power increasing from 63.7 to 403.5 mW, the pulse repetition rate increases from 48.5 to 121.2 kHz accordingly. Meanwhile, we observe that the pulse width was shortened from 3.54 μs to 890 ns. The experimental results prove that germanene nanosheets have a promising future as a Q-switcher in fiber lasers.

In this paper, a new approach for the design of wideband bandpass frequency selective surface (FSS) is proposed based on the microstrip patch resonator and substrate integrated waveguide (SIW) cavity. Originating from the similarity of field distributions between the patch and SIW resonators, the patch resonator is concentrically embedded within the SIW cavity. In this context, resonant modes in both patch resonator and SIW cavity can be generated without enlarging the circuit size. Then, the slotlines are introduced to the ground layer to establish cross-couplings to produce transmission zeros (TZs) for better out-of-band performances. For demonstration, a fourth-order bandpass FSS is constructed, simulated, and fabricated. The measured results agree with the simulated ones, verifying that the proposed design method possesses attractive advantages of low profile, compact size, high frequency selectively, and nice universality.

A metal-loaded double-layer unidirectional radiation slot antenna with flat gain is proposed for millimeter-wave (mm-wave) operations. Our presented antenna is constituted of a slot antenna with metal vias, an inner floating metal, a metal line, and ground patch. With the help of inner metal excited by the coupling of the slot antenna, an additional resonance point around 26 GHz could be obtained and the antenna gain is enhanced. To verify the design, the antenna has been fabricated with the prepreg technology. The whole fabricated size is only 0.62 × 0.62λ₀² with a thickness of 0.057λ₀ (λ₀ is the free-space wavelength at 26 GHz). The measured impedance bandwidth is from 25.1 to 26.55 GHz. Moreover, the proposed antenna obtains a wide flat gain (5.78 ± 0.48 dBi) within the bandwidth and stable one-sided radiation patterns. The above characteristics show that the proposed antenna is a competitive choice for mm-wave systems.

This article proposes a switchable filter with four operating states, namely dual-band mode, lower band mode, upper band mode, and all-stop mode. The transition between these states is achieved by using positive intrinsic negative diodes, while the center frequency tuning is done by using varactors. In order to verify the design concept, a prototype has been fabricated on an F4BME substrate with a dielectric constant of 2.25 and a thickness of 1 mm, and the measured results were in agreement with the simulations. Notably, the dual-band mode yields four transmission zeros (TZs), while the single-band mode produces two TZs. The final circuit size of the designed filter is 0.18 × 0.14 λg, making it ideally suited for reconfigurable multi-band communication systems.

Ten to 25 μm-long-wavelength mid-infrared laser has broad application prospects in fields such as military, industrial, medical, and spectroscopy. Currently, lasers capable of emitting 10–25 μm-long-wavelength mid-infrared radiation include CO₂ lasers, solid-state lasers, quantum cascade lasers, infrared supercontinuum light sources, and free electron lasers. This review summarizes the development status of these five types of lasers, providing a detailed analysis and summary of their operating principles, advantages, limitations, and future outlooks. The aim is to offer valuable reference information for related research and to promote the further development and application of tunable mid-infrared laser at 10–25 μm.

This paper presents a novel design method for a tri-band multiple in multiple out (MIMO) antenna. The antenna consists of four sets of identical antenna pairs arranged on the two side frames. Three resonant modes can be obtained using a microstrip coupling feed structure by employing different branches in antenna unit design. The working frequencies of the modes can be adjusted independently. Moreover, in each pair of antennas, two antenna units were closely arranged and a decoupling grounding branch was employed between the adjacent antennas to ensure good isolation. The tri-band eight-element MIMO antenna operates at 3.5, 4.9, and 5.6 GHz and the isolations were better than 14 dB. The proposed antenna had a low profile of 0.06$��{\lambda }_0�$ and good isolation so it has potential applications in 5G mobile terminals.

A novel equation for array beam pattern synthesis is presented. The expected pattern total power is set to a fixed value, under this constraint, the difference between the main beam total power and the other part total power is maximized to achieve the array pattern synthesis. To solve the proposed pattern synthesis equation, which cannot be solved by any published traditional method, based on the Lagrange multiplier method, it is transformed into a new equation in which the array element excitation vector is the eigenvector of a matrix. Thus, the array element excitation vector can be obtained by matrix eigenvalue decomposition. Three array architectures using the method are taken as examples to show its advantages. Simulation results of the examples show that the method has better performance than other methods. The method is a noniterative approach, so it requires less computational volume to complete the pattern synthesis process. In addition, through eigenvalue decomposition, multiple eigenvectors can provide other different solutions of array elements current excitations, which can be applied in different areas.

A single-channel transmitarray antenna with abilities of super resolution and digital beamforming (DBF) is proposed. The amplitude and phase distributions on the array aperture are reconstructed through beam switching with a single channel. By finding and solving relations between distributions and received signals of beams, aperture distributions can be reconstructed. The ill-conditioned problem caused by limited scanning range and angular interval is solved using the regularization method. The obtained distributions can then be delivered to super-resolution algorithm to obtain super resolution, or used to produce shaped beams by DBF. On the basis of the proposed theory, a bifocal beam-reconfigurable transmitarray is designed and tested as a single-channel DBF antenna without special and additional hardware design. It has the outstanding advantages of low cost, simple structure, low energy consumption, and high working frequency.

Aimed at the interconnection between coaxial transmission line and substrate-integrated waveguide (SIW), a wideband coaxial-to-SIW transition was proposed and applied in a 1-to-4 radial power divider. First of all, a fan-shaped region was designed on the end of a SIW transmission line. Then, a coaxial transmission line was inserted into this region. To improve the impedance matching at the coaxial port, a feeding ring was designed on the back of the transition where the coaxial line was inserted. Next, the transition was applied in a 1-to-4 radial power divider to realize an equal power division. Finally, to validate the correctness of the designs, prototypes were fabricated and measured. For the coaxial-to-SIW transition, measured reflection coefficient |S₁₁| was less than −15 dB from 7.84 to 12.18 GHz. Transmission coefficient |S₂₁| was between −0.52 and −0.24 dB. For the 1-to-4 radial divider, measured |S₁₁| was less than −15 dB from 7.91 to 12.4 GHz, and the transmission coefficient was around −6.9 dB. Measurement and simulation agreed well with each other. Therefore, the proposed design can be used in coaxial-to-SIW interconnection scenarios.