Microwave and Optical Technology Letters最新文献

A novel filter design is proposed that employs harmonic rejection characteristics based on half-mode substrate-integrated waveguide resonance cavities and microstrip resonators. The objective is to expand the filter's blocking bandwidth and reduce the filter's size. The filter employs two half-mode substrate-integrated waveguide resonant cavities, which serve to effectively reduce the size of the filter. Moreover, the higher-order modes TE₂₀₁ and TE₂₀₂ are unable to propagate within the resonant cavities. The suppression of the TE₁₀₂ mode is achieved by setting the coupling window between the resonant cavities at the weakest field strength of this mode. Concurrently, two microstrip resonators are integrated into the coupling window, thereby enabling the realization of a fourth-order filter response with only two resonant cavities. The filter was processed and measured, and the results were found to be in good agreement with the simulation. It is proved that the design method proposed in this paper is feasible.

A two-channel high-selectivity, wideband bandpass filter has been presented. This is based on a microstrip mixed-impedance resonator and defected ground structure with the mixed coupling strategy. Two pairs of peripheral stepped-impedance resonator (SIR) structures are used as stubs, achieving TZs at the immediate lower and upper cut-off sides of the passband and control the bandwidth, while the other two transmission zeros on the upper cut-off side are yielded through the defected ground structure, and the coupling between the SIR and uniform-impedance resonators components, respectively. A prototype of the circuit is fabricated and measured for validation. The measured results exhibited insertion and return losses better than 1.1 and 20.5 dB, respectively, and high isolation levels exceeding 19 dB. In total, four transmission zeros are achieved. The designed filtering circuit realized a 3-dB fractional bandwidth of 58.1%. There is a 0.95f₀ stopband at the upper cutoff. The fabrication of the prototype shows good agreement between the simulated and measured performance.

The TiS₂ compound has attracted considerable attention among researchers in the fields of energy storage and conversion, as well as semiconductor materials. This is due to its remarkable capability to incorporate various elements into its van der Waals gap, as well as its potential to adjust the carrier concentration within the material to optimize its electrically relevant properties. In our study, we employed a terahertz (THz) time-domain spectroscopy system to measure the spectra of TiS₂ within the THz frequency range. Through this analysis, we examined the optical parameters, such as transmittance and refractive index, of the TiS₂ samples. Additionally, we conducted optical pumping correlation experiments using THz detection technology to investigate the optical pumping effects on TiS₂. By analyzing the THz energy transmission process in different states, we were able to calculate and fit the carrier recombination time. The findings of our research hold significant implications for the advancement of THz devices operating in the 6G frequency band.

We propose a novel approach to dual-channel optoelectronic oscillators (OEOs) with enhanced frequency band by leveraging directly modulated (DM) semiconductor lasers under optical injection. In this configuration, the frequency-tuned optical signal from a master laser is introduced into a single-mode slave laser, facilitating multioptical-mode operation. The resulting multiple optical frequencies emitted by the slave laser facilitates a DM-OEO signal at a frequency exceeding the laser's intrinsic modulation bandwidth. Through the deployment of a dual-channel OEO based on the DM multimode laser signal, stable oscillation signals have been successfully achieved simultaneously at 15 and 18 GHz with phase noise levels of 96.43 and 95.62 dBc/Hz, respectively, at a 10-kHz offset frequency.

In this study, a frequency-reconfigurable circular patch antenna with a varactor diode has been presented. The proposed antenna has been designed and investigated in four steps: circular patch antenna (Antenna 1), antenna with double slots (Antenna 2), antenna with quad slots (Antenna 3), and antenna with varactor diode (Antenna 4). The proposed antenna has been made compact with rectangular slots and a hyperabrupt junction tuning varactor diode (SMV1249-079LF). The proposed antenna has been designed and produced in 32 × 32 × 0.64 mm³ dimensions, approximately 80% minimized compared to a microstrip circular patch antenna operating at 850 MHZ resonance frequency. This frequency-reconfigurable antenna can perform between the range of 0.85–1.3 GHz frequency with 0–3 V DC voltage tuning of the varactor diode. So, using with the varactor diode, the proposed antenna has obtained a 53% tuning range between 0.85 and 1.3 GHz frequencies. This study offers a different antenna design, compactness, and high tuning ratio compared to previous studies. This frequency reconfigurable antenna can be preferred with its wideband structure in different communications areas and wireless energy transfer systems.

In this letter, a mm-wave monolithic ceramic waveguide filter using a transition between a grounded coplanar waveguide (GCPW) feed and a ceramic waveguide has been proposed. The published studies on monolithic ceramic waveguide filters with wideband properties for the mm-wave are lacking. A desired external quality factor, satisfying wide bandwidth, is achieved using both inductive and capacitive couplings in the transition. The inductive coupling is realized with a waveguide's hole directly connected to the microstrip line probe of the GCPW. The capacitive coupling is employed with the slots of both GCPW and ceramic waveguide, which are placed facing each other. Adopting the presented transition, the inline monolithic ceramic waveguide filter for a fourth-order Chebyshev response was designed. The fabricated filter provided the insertion and return losses of lower than 1.2 dB and higher than 10 dB, respectively, at frequencies from 26.43 to 29.76 GHz, with a fractional bandwidth of 11.85%.

Fano resonance (FR) and the triggered nonreciprocal thermal radiation (NTR) in a Weyl semimetal (WSM)- incorporated Kretschmann configuration has been observed and analyzed. Employing the anisotropic permittivity tensor, the electromagnetic responses of the proposed layered structure have been studied, and we illustrate that FR and strong nonreciprocity is attributed to the coupling between the planar waveguide mode and surface plasmon polaritons in WSM. It is shown that absorptivity (α) is not consistent with emissivity (e) in the considered angular range, which confirms near-complete violation of Kirchhoff's law with nonmagnetic WSM. To analyze the physical origin of NTR, we performed numerical calculations for the α, e, nonreciprocity (η), as well as the magnetic field inside each layer. The compre-hensive investigation of η with regard to geometric parameters suggests great potential for the practical use of perfect absorption and NTR over a wide range of frequencies and layer thicknesses.

A 220 GHz GaN-based monolithic integrated frequency doubler with high continuous-wave output power has been developed. The doubler achieves improved heat dissipation by establishing the terahertz (THz) monolithic integrated circuit topology with GaN Schottky barrier diodes integrated on a high thermal conductivity SiC substrate. It features six anodes to enhance the power-handling capabilities. A refractory Schottky metal stack is adopted for better thermal stability. The doubler realizes satisfactory performance by introducing the suspended microstrip and an all-in-one output structure. For verification, a prototype of the proposed frequency doubler was fabricated and tested. Measured results show that the proposed doubler produces a continuous-wave output power of 255 mW at 220 GHz with an efficiency of 14.6%, exhibiting excellent potential for powerful THz sources.

A wideband transmitarray antenna (TA) incorporating a polarization conversion metasurface (PCM) is proposed. Four PCM elements with annular metallic polarizers are utilized to provide 2-bit phase compensation without altering the geometric parameters of the elements, resulting in a wideband TA with a bandwidth comparable to that of the individual elements. A prototype of the proposed TA is designed, fabricated, and measured. The measured 1- and 3-dB gain bandwidths of the proposed TA are found to be 10–13.6 GHz (30%) and 9.2–15 GHz (48.3%), respectively, while the effective 1-dB transmission band of the individual elements is 7.8–14.6 GHz. The similarity between the bandwidth of the proposed TA and that of elements used in our design demonstrates less wastage of element bandwidth by the proposed approach. A measured peak gain of 27.2 dBi and a peak aperture efficiency (AE) of 48.7% highlight the promising potential of the proposed TA for long-distance communication, point-to-point communication, and other applications.

This article introduces a unique design approach for a compact in-band full-duplex (IBFD) antenna with good isolation in a wider bandwidth at the 2.4 GHz WLAN. The meander slot baluns are innovatively constructed in the feeding network, one balun on the top substrate layer and the other on the bottom substrate layer of the ground, to realize double differential feeding and polarization diversity. The metallic vias that connect one of the baluns in the feeding network with the co-radiating patch further reduce the antenna's overall size. The balun's neutral coupling characteristics of differential potentials, which reduce the leakage currents by creating null potential, and differential filtering, which suppresses the leakage currents by non-coupling fields, generate high isolation in the antenna. The designed balun offers a stable differential feed with a trivial magnitude and phase imbalances of (0.04–0.06) dB and $��\pm �\; �1^0�$, respectively. The antenna offers a minimum isolation of 78 dB with a wider bandwidth of 130 MHz. The far-field measurement shows broadside radiation with low cross-polar levels of less than −32 dB. A prototype is fabricated on FR-4 substrate layers with an overall size of (0.8 × 0.8 × 0.012)$��{\lambda }_0�$ ($��{\lambda }_0�$ is the free space wavelength of the frequency $��f_0�\; �=�\; �2.4�$ GHz) to validate the proposed design performance. The measured results of the prototype properly correlate with the simulated results.