Microwave and Optical Technology Letters最新文献

In contemporary communication systems, especially military radar systems, there is a significant demand for low-profile, wideband, high-gain antennas that can operate across the X-band (8–12 GHz). Despite numerous studies on X-band antennas, they are often characterized by limitations such as low gain, narrow bandwidth, or a high profile. This letter presents a monopole array antenna that combines the advantages of low-profile, wideband, and high-gain. And a parallel feeding network based on a quasi-microstrip structure is designed in this letter, which solves the problem of difficult feeding for this type of array. Through parameter optimization of the array antenna, its overall size is obtained as 76 mm × 63 mm × 5 mm, with an operational frequency range of 7.4–13.3 GHz and a relative bandwidth of 59%. Rigorous measurement of the array antenna's prototype has been conducted, revealing a high degree of congruence with simulation results. The measured results show that the antenna has a stable gain in the range of 13–14.3 dBi, and the highest measured aperture efficiency reached 47%. It is facile to fabricate and readily integrates with communication systems. This design also has a certain promotional effect on the research of wideband antennas.

For the first time, a miniaturized wideband four-way unequal filtering power divider (FPD) based on asymmetric three-coupled lines (A-TCLs) is proposed. Two stepped-impedance resonators (SIR) are loaded on the A-TCL for enhancing the frequency selectivity and out-of-band rejection. Besides, two types of resistors are loaded for good output impedance matchings and isolations. Design equations are derived by combining the methods of even-odd mode decomposition and voltage-current analysis. For validation, a prototype with a power division ratio of 1.8:1:1:1.8 is designed. Measurements show that an overlapped bandwidth of more than 60% is obtained with low insertion loss, large out-of-band rejection and high frequency selectivity. In addition, the overall size is 0.43λ_g × 0.32λ_g, which is the smallest one in the state-of-the-art four-way FPDs.

In this paper, a wide band tapered rod two-element MIMO antenna system is designed using a perforated H-guide section for W-band applications. The antenna system comprises of a metallic housing and a perforated H-guide section with tapered input/output dielectric sections. The dielectric section is sandwiched between the two halves of the metallic housing. The designed MIMO antenna is fed by a pair of WR-10 rectangular waveguides. The perforations in the dielectric section not only provide the mechanical stability to the structure but also facilitate high inter-port isolation. The MIMO performance of the designed antenna system is calculated with reference to envelope correlation coefficient (ECC), diversity gain (DG), and channel capacity loss (CCL). These parameters are below the satisfactory range of 0.5, 10 dB, and 0.4 bit/s/Hz. High gain (> 12 dBi), high port-to-port isolation (> 28 dB), and end-fire radiation characteristics of the designed antenna system, make it a potential candidate for W-band communication systems.

A broadband circularly polarized metasurface antenna is proposed. The initial metasurface structure is first diagonally chamfered and a rectangular slot is etched at the chamfer. The chamfering operation can cause an imbalance in the surface impedance of the hypersurface patch, and this imbalance creates a phase difference between the incident wave and the reflected wave, which is considered to be circularly polarized when the phase difference is close to 90° and the amplitudes of the two are equal. Analyze the metasurface structure after chamfering using the characteristic mode theory (CMT), further optimize it based on the obtained characteristic mode analysis results, and analyze it again using the characteristic mode. Finally, two target modes with a phase difference close to 90° were formed. The two characteristic modes are successfully excited by microstrip slot-coupled feeding structure to achieve circularly polarized radiation of the antenna. Finally, the antenna is fabricated and measured. Based on the measured results, it can be observed that the antenna has 35.4% −10 dB impedance bandwidth, and 17% 3 dB axial ratio bandwidth, and the antenna simulated and measured results match.

This letter proposes a novel single-layer dual-polarized (DP) millimeter wave (mmWave) low-profile antenna. This antenna is based on a circular substrate integrated waveguide (SIW) resonant cavity. Two different resonant cavities are created by incorporating via fences internally: a conventional circular resonant cavity and a circular ring resonant cavity. The bandwidth is expanded by introducing a central via in the internal resonant cavity, which generates the TM₀₁₀ and TM₁₁₀ resonant modes. On the other hand, the external annular resonant cavity introduces the TM₄₁₀ and TM₅₁₀ resonant modes by carefully adjusting the size of the radiation slot. The radiation slots within the external annular resonant cavity and the inner circular resonant cavity are positioned orthogonally, enabling dual-polarized (DP) operation. It is shown that the DP antenna can achieve the measured −10 dB impedance bandwidths (FBW) of 11.82% (26.26–29.56 GHz) and 11.15% (26.09–29.17 GHz) for port 1 and port 2, respectively. The antenna features stable radiation patterns with an average gain of 5.1 dBi and a high isolation exceeding 20 dB within the passband. The antenna exhibits a single-layer structure, low profile, high-isolation, and low-cost advantages, which can be a good candidate for 5G mmWave indoor applications.

We present a single longitudinal mode Ho:YLF MOPA laser operating at 2050.7 nm by utilizing the Fabry–Perot etalon method to construct a compact SLM seed laser and employing Tm-doped fiber as the amplifier. With an output power of 336 mW generated by the seed laser, the maximum output power of 13.1 W for the single longitudinal mode MOPA laser was recorded at a pump power of 88.7 W. A peak slope efficiency of 26.9% was achieved when the pump power exceeded 58.7 W. To our knowledge, this is the first report of utilizing Tm-doped fiber to amplify the SLM operation of Ho:YLF laser.

This paper presents a novel compact balanced-to-single-ended out-of-phase filtering power divide with continuously tunable center frequency and bandwidth. By introducing a T-shaped slot on the isosceles right triangle patch resonator to perturb the TM₁₀ mode and exploring varactors-loaded stubs, a new tunable miniaturized patch resonator is created. The proposed filter comprised three new tunable patch resonators connected by back-to-back varactors to adjust bandwidth in between. By studying the electric field distribution of the odd mode TM₁₀ and grounded isolation resistors, the wished out-of-phase output signal and good port-to-port isolation can be generated. Based on such a simple structure, a balanced-to-single-ended out-of-phase filtering power with tunable bandwidth is designed and realized with a center frequency tuning range covering from 1.60 to 1.95 GHz (19.7%) and 3-dB bandwidth tuning range covering from 265 to 328 MHz at 1.90 GHz.

The monolayer WSe₂ material was utilized for a saturable absorber to create a 2.7 μm passively Q-switched pulse laser. The maximal single pulse energy was 2.75 µJ, and the highest peak power was measured approximately 2.53 W. As far as we know, this is the first instance of monolayer WSe₂ being used for passive Q-switching operation in mid-infrared. The results provide favorable evidence for monolayer WSe₂ as a mid-infrared Q-switcher and show the promise of monolayer two-dimensional materials for ultrafast pulsed laser applications.

The present work deals with the performance investigation of bandwidth-efficient optical fiber communication systems. In this paper, novel 2-D orthogonal hybrid optical modulation techniques are proposed. In the proposed fiber optic communication system for dense wavelength-division multiplexing (DWDM), optical modulation techniques minimum shift keying (MSK) and pulse amplitude modulation (PAM) are simultaneously modulated at 100 GHz channel spacing with a minimum utilization bandwidth of 4.3 THz. The results show a significant advantage in using the proposed hybrid optical modulation techniques in offering high bandwidth optical signal-to-noise ratio with an acceptable quality factor.

In this paper, a novel partially reflective metasurface (PRS) unit is proposed for beam deflection in a dual-band shared aperture Fabry–Perot cavity antenna (DB-FPA). It operates in the C-band and X-band. Independent control of different frequency bands can be achieved by adjusting the different parameters of the PRS unit. A coaxially fed patch antenna is used as the feed source for the proposed antenna. This antenna exhibits high aperture efficiency and can operate in two bands with a ratio of 1:1.67. The measurements indicate the impedance bandwidth $��\; ��\left|�\; �S_{11}�\; �\right|�\; �<�\; �-�\; �10��$ dB of the DB-FPA is 5.54-6.48 GHz (15.6%) and 9.62–10.52 GHz (9%). The gain is 7.15 dBi at 6 GHz with an aperture efficiency of 34.8%, and 8.3 dBi at 10 GHz with an aperture efficiency of 14.5%. The beam deflection of $��\; ��{22}^{\circ }��$ at 6 GHz and $��\; ��-�\; �{54}^{\circ }��$ at 10 GHz.