Microwave and Optical Technology Letters最新文献

This letter presents a 28 GHz balun-first low noise amplifier (LNA) featuring a wide dB-linear variable gain range. The architecture of LNA includes three-stage cascode amplifiers. An integrated balun at the input stage provides RF ESD protection and converts a single-ended signal to a differential one (S-to-D). A transformer-based dual-resonant matching network is designed and analyzed to achieve wideband performance. To realize a continuous dB-linear variable gain range and consistent input/output matching, gain control is implemented in the second stage using a 5-bit digital-to-analog converter (DAC) for a 32 dB gain range. The DAC can generate a nonlinear analog voltage to control the gate of the common-gate transistor in the second cascode stage, inversely compensating for the nonlinear gain variations of the cascode amplifier. The LNA is fabricated in 65-nm CMOS process with a core size of 0.154 mm². Measurement results exhibit a maximum gain of 33.5 dB and a minimum noise figure (NF) of 3.65 dB with a 3-dB bandwidth of 23–29.5 GHz. The measured variable gain range is approximately 32 dB across 32 different gain states, with a linear gain step of ~1 dB per state and an IP1dB ranging from −6.5 dBm to −35.25 dBm. The power consumption is 35.4–48 mW from a 1.2 V supply voltage.

This paper presents a low-scattering 1 × 2 patch array antenna combining resistive and coding metasurfaces (MSs) for the reduction of wideband-backscatter. An artificial magnetic conductor technology is used to validate the proposed technique, which is fundamentally based on scattering, phase cancellation, and absorptive property of the MS. By integration of coding MS elements and an absorbent unit cell, three different array blocks are utilized to significantly reduce the monostatic and bistatic backscattered energy level from 6.5 to 16.5 GHz, as well as overall reduction from 5 to 22 GHz. Under the incidence of plane waves, various reflection phases have been observed. The diffusion of the scattering energy from the surface can be achieved by carefully choosing the phase distributions for the reflected waves. Additionally, the bistatic backscattered energy level of the prototype is realized at various frequency points. This technique is validated using artificial magnetic conductors, which uniquely combine the effects of scattering, phase cancellation, and absorption in the MS's hybrid unit cells. Further, antenna array parameters are optimized for frequency, polarization, and angular diversity, S-parameters, radiating efficiency, reducing radar cross section (RCS) in the wideband range and ensuring robust performance. The experimental results were substantiated by simulations of the reference and proposed prototypes suggesting that the proposed prototype can be a good candidate for applications that require a low monostatic and bistatic RCS platform.

In this letter, we investigate the radio propagation characteristics in an open outdoor place through a frequency-domain channel measurement campaign at a frequency band of 2.1 GHz via asymmetric beam patterns. Specifically, we focus on the large-scale fading characteristics and analyze the transceivers' separation-dependent and boresight direction-dependent received power, shadow fading (SF), and SF auto-correlation properties under the case of perfect beam alignment. Furthermore, the effects of asymmetric beamwidths are also thorough investigated. The measured results reveal that transceivers' beams can reduce the shadow fading variances evidently in contrast to the omnidirectional antennas' case. Besides, it is found that the pattern where mobile receiver (Rx) uses narrow beams and static transmitter (Tx) adopts the omnidirectional antenna yields a high SF auto-correlation value compared to the other beam patterns. The conclusions help to understand the impacts of variable beamwidths on radio propagation.

The surveillance and assessment of the total viable count (TVC) of Staphylococcus under different levels of catheter contamination are crucial for the prevention and evaluation of catheter-related infections in hemodialysis (HD). This paper demonstrates the noninvasive and accurate measurement of the TVC of Staphylococcus using wavelength-modulated tunable diode laser absorption spectroscopy (WMAS). The tunable distributed feedback laser with a central wavelength of 2004 nm was employed and the detection limit of 22.5 ppm for carbon dioxide (CO₂) produced by Staphylococcus epidermidis was obtained. The growth of Staphylococcus under different medium concentrations was studied, and the results indicated a strong correlation between the growth rate and final TVC of S. epidermidis with the medium concentration. When the degree of catheter contamination was low, resulting in minimal residual nutrient concentration within the catheter, the bacterial growth rate and TVC were effectively suppressed. Therefore, it is proven that WMAS is a user-friendly, noninvasive, and high signal-to-noise ratio technique for monitoring Staphylococcus, making it an effective tool for assessing Staphylococcus growth in HD catheter surveillance.

This paper proposes a simple tri-band impedance transformer for frequency-dependent complex impedances. The proposed transformer is a cascade of a π-model transformer, three series transmission lines, and a tri-band susceptance stub network, the structure is simple, and the matching sequence of the three frequencies can be changed. All parameters of the design can be obtained from the derived analytical formulas, and the process of the design is elaborated. Two design examples demonstrate the proposed design method, and a prototype is fabricated for verification. Good agreement between the simulated results and measured results is obtained. Compared with the existing works, the transformer features a simple structure, offering flexibility to match frequency-dependent complex impedances, and a simple method. Additionally, it features a very short total electrical length and wider bandwidth. Therefore, the proposed transformer is suitable for the tri-band active circuits and wireless communication systems.

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.