Microwave and Optical Technology Letters最新文献

This article introduces a compact planar antenna for implantable neurostimulation devices that ensures efficient and reliable communication with handheld devices while minimizing battery drainage. The antenna design operates within the 2.4–2.48 GHz frequency range, suitable for the 2.45 GHz ISM band. A cubical shell, created using 3-D printing technology, was employed to evaluate the antenna's performance on pig tissue models. Reflection coefficient measurements and Specific Absorption Rate (SAR) analysis were conducted to assess safety and functionality. The newly designed antenna demonstrated an impedance bandwidth ranging from 2.2 GHz to 2.67 GHz when integrated into the device and positioned between pig tissues. The SAR analysis confirmed that the antenna adheres to safety standards for electromagnetic exposure. The antenna effectively maintains communication capabilities and meets safety standards when embedded within the human body, thus addressing key challenges in implantable device functionality due to antenna detuning. This study contributes significantly to the field of implantable biomedical devices, offering a viable solution to communication effectiveness while ensuring energy efficiency and safety compliance, thereby improving long-term device functionality.

This article presents a near-field, electronically polarization-reconfigurable, lightweight, low-cost millimeter-wave antenna system featuring a fully metallic metasurface (FMM) superstrate over a 3D-printed pyramidal horn antenna. The proposed unit cells of the FMM superstrate consist of three identical metallic layers, each adorned with periodically perforated L-shaped structures at every corner, along with a central horizontal rectangular slot. The antenna prototype supports LHCP, LP, and RHCP polarization configurations through three different electronic axial rotations of the FMM superstrate at the horn antenna's aperture. Both simulations and experiments are conducted to validate the antenna design, demonstrating good agreement and confirming the feasibility of the proposed design. The antenna achieves a 3 dB axial ratio (AR) bandwidth of 400 MHz, with a maximum realized gain reduction of 0.5 dB and a peak gain of 21.6 dBi at 30.1 GHz, while maintaining an excellent side lobe level of −21 dB.

In this letter, a wideband filtering dielectric resonator antenna is proposed. The antenna consists of a hybrid dielectric block and four dielectric blocks with metal vias. The hybrid dielectric resonator is surrounded by the four dielectric blocks with metal vias. It is fed by a microstrip feedline with two bent transverse stubs. The dielectric blocks with metal vias can generate two radiation nulls at band edges, thereby realizing the filtering function. The two laterally bent branches of the microstrip line, which differ in length and shape, excite an additional resonant mode that improves impedance matching and enhances suppression in the upper stopband. This study exhibits a 10-dB impedance bandwidth of 42% (2.27–3.44 GHz), a peak gain of 7.35 dBi. To prove the correctness of the simulation, the antenna prototype is fabricated and tested. The experimental measurements closely match the simulation results.

Inverse design based on high-performance computing ability is an efficient and intuitive design method. In this paper, we employed the digitized adjoint method to design a symmetric 3-dB power splitter based on N-ary digital pattern with an occupied compact footprint of only 3.25 µm × 2.6 µm. The digitized adjoint method is applied to inverse design and continuously adjusts and updates the relative permittivity for a cylindrical material filled with the intermediate material to obtain a quasi-digital pattern and then transforms it into a quaternary digital pattern. Based on this approach, a symmetrical structure with etching cylindrical radius of 45, 37, and 30 nm was obtained, which enables the 3-dB power splitter to achieve a precise 50:50 split ratio in a wide wavelength range from 1.45 to 1.65 µm. And the excess loss (EL) was less than 1 dB with an operating bandwidth of 200 nm. This approach holds significant potential for informing the design of high-performance, compact power splitters.

Metasurfaces provide an unprecedented capability for manipulating electromagnetic waves. In this study, a wideband and high-gain folded transmit-array antenna (FTA) based on a 3-bit Fabry–Perot transmission polarizer (FPTP) metasurface was proposed and realized. The proposed FTA comprises three key components: (1) top-layer FPTP metasurface, (2) bottom-layer miniaturized waveguide horn feed, and (3) reflector array. The FPTP metasurface adopts a sandwich structure, integrating two orthogonal metallic grids with an embedded 3-bit digitally encoded C-shaped ring, which simultaneously achieves polarization conversion and high-precision phase compensation while avoiding insertion losses caused by multilayer stacking. The feed employs a customized miniaturized waveguide horn, and the reflector incorporates a 90° polarization conversion function, effectively mitigating the impact of missing central elements in the primary reflector without requiring additional polarization layers. Through synergistic optimization of the FPTP metasurface, feed, and reflector, the system achieves high-gain and wideband performance while maintaining a low-profile geometry (thickness reduced to one-quarter of the focal length). A prototype with 45 × 45 unit cells was fabricated and tested, demonstrating an operational bandwidth of 11.3–17 GHz, a measured peak gain of 27.1 dBi, a 3-dB gain bandwidth of 36.4%, and an aperture efficiency of 38%, all of which align closely with simulations. The proposed 3-bit FPTP metasurface provides a novel solution for low-profile, high-gain antenna design and is expected to find potential applications in next-generation wireless communication systems.

This paper presents a series of mode-composite bandpass filters (BPFs) and diplexer, which integrate both electro-magnetic (EM) and source-load (SL) coupling within the hybrid eighth-mode substrate-integrated waveguide (EMSIW) and microstrip line (MSL) resonators. The mixed EM coupling can achieve a distinct distribution of transmission zeros (TZs), and SL coupling can further enhance the selectivity near the operating passband. Case I presents a mode-composite BPF operating at 3.5 GHz. The proposed BPF employs SL coupling and EM coupling, with electric coupling (EC) being predominant. Consequently, this configuration yields three TZs adjacent to the passband: one to the left and two to the right. Case II presents a similar BPF design operating at 5.6 GHz, but with magnetic coupling (MC) dominating the mixed EM coupling. This configuration also results in three TZs near the passband: one to the right and two to the left. To demonstrate and validate the novel property, both types of mode-composite BPFs and the relevant diplexer have been designed, fabricated, and measured. The simulation and measurement have reached to a satisfactory agreement.

In this letter, we propose a broadband bandpass filter featuring controllable notch bands and a wide stopband, utilizing fan-shaped substrate integrated waveguide (FSSIW) and spoof surface plasmon polaritons (SSPPs). Rectangular slots arranged in a quasiperiodic pattern are carved into the central part of the upper metal of the FSSIW structure to support SSPPs mode. The dispersion curve of the quasiperiodic FSSIW-SSPPs unit structure is analyzed, which demonstrates that the quasiperiodic FSSIW-SSPPs unit structure is suitable for developing wideband bandpass filter. By modifying the geometric characteristics of the FSSIW and SSPPs structures, the lower and upper cutoff frequencies of the bandpass filter based on the Quasiperiodic FSSIW-SSPPs unit can be controlled independently. Utilizing the wideband bandpass filter as a foundation, coupling U-shaped resonators at the input and output terminals of the filter generates a notched band in the passband. The novel developed a wideband bandpass filter featuring a frequency notch that exhibits measured passbands spanning from 7.640 to 9.183 GHz and from 9.343 to 10.503 GHz. This filter with a notched band offers the benefits of compact lateral dimensions and a broad stopband.

In this article, a compact 28/38 GHz dual-band endfire phased array is presented for 5G millimeter-wave (mm-wave) mobile terminal applications. The unit cell is a planar dipole printed on a single substrate layer. Parasitic strips and etched slots are loadedon the dipole to construct different current paths in 28 GHz and 38 GHz, thus achieving dual-band operation with a single radiator, leading to a small ground clearance of 1.6 mm. A 5-element array with 5-mm element spacing is fabricated. The measured -10 dB impedance bandwidths are 11.7% (26.9–30.2 GHz) and 13.1% (36.5–41.5 GHz) in the two operating bands with isolation higher than 16 dB. The measured peak gains attain 8.5 dBi and 10.4 dBi in the lower and upper bands. The phased array supports a beam scanning angle of –51° to + 50° at 28 GHz and –39° to +37° at 38 GHz.

In this study, we demonstrate an intracavity frequency-doubled 532-nm laser with a high peak power and narrow pulse width based on an LED-pumped electro-optically (E-O) Q-switched Nd:YAG laser. In the Q-switched operation mode, a maximum output of 4.35 mJ pulse energy at 1064 nm was obtained at a repetition rate of 200 Hz with a duration of 88 ns and a peak power of 50 kW. By optimizing the incidence angle of the KTP crystal to satisfy the noncritical phase-matching condition, the output pulse energy for the green laser at 532 nm was 1.55 mJ at a repetition rate of 200 Hz with a duration of 46 ns and a peak power of 33.7 kW by intracavity frequency doubling. To the best of our knowledge, this is the first demonstration of LED-pumped E-O Q-switched 1064- and 532-nm lasers reported to date.

Steering the radiation pattern to the desired direction is highly anticipated for smartwatch GPS antenna in user scenarios, as it prevents energy from being wasted in unnecessary directions. In this paper, a dual-pattern reconfigurable metal-bezel smartwatch GPS antenna is proposed, which is capable of concentrating radiation energy according to different wearing preferences. The smartwatch consists of a metal bezel and a ground plane. An L-shaped branch is introduced, enabling current coupling into the clearance. With only two switches, opposite localized current paths can be achieved within the clearance, contributing to different radiation patterns. As a result, the antennas' peak gains of −0.70 dBi and −0.84 dBi are achieved at 1.575 GHz, respectively, which are suitable for left-wrist and right-wrist wearing scenarios. Antenna prototypes were fabricated, with the measured results agreeing well with the simulated ones. The L-shaped branch can be realized by laser direct structuring (LDS). The simple and practical implementation offers a feasible solution for enhancing the performance of smartwatch GPS antenna.