Microwave and Optical Technology Letters最新文献

This letter proposed a high-gain and high-directivity bow-tie antenna array (BTAA) with a composite reflector (CR) and a gradient refractive index (GRIN) lens. The CR is composed of two types of units with different mechanisms while the GRIN lens consists of eight metamaterial units with different refractive index. The measured results show that the maximum gain of the target antenna is 13.22 dBi, antenna gain is improved about 4.75 and 1.15 dB based on these structures, respectively. In addition, the minimum value of half-power beamwidth (HPBW) in xOz plane is 37.1 degrees, the maximum value of the sidelobe level is -10.19 dB, the proposed antenna has a good directivity in operation band. The simulation and measurement results demonstrate that proposed antenna has a good application potential in shallow GPR systems.

Microwave-photonics technology enables advanced radar systems by leveraging high bandwidth and low-loss signal processing for enhanced target detection and tracking. This paper presents the design and implementation of an X-band photonics-assisted continuous wave radar system, specifically developed for the detection and parameter estimation of small unmanned aerial vehicles (sUAVs) using micro-Doppler time-frequency analysis. The system incorporates a novel image-based processing algorithm that extracts critical rotor characteristics, such as rotational speed, blade length, and tip velocity. A detailed link-budget and hardware configuration, including intermediate frequency signal parameters, low-noise amplifier range, and analog-to-digital converter specifications, are presented to support system performance evaluation. Extensive open-field experiments were conducted on multiple real-time targets—including two-blade, three-blade, and flapping-wing sUAV models—with varying tilt angles and ranges up to 75 m. The system demonstrated the ability to detect up to four simultaneous targets, with a measurement accuracy ranging from 91.8% to 99%. This study contributes a scalable radar architecture and robust detection framework for security-critical applications, such as drone surveillance, reconnaissance detection, and autonomous threat tracking.

This paper presents a passive wireless flexible strain sensor with reconfigurable frequency selectivity inspired by kirigami. The sensor is composed of a rectangular complementary split-ring resonator (CSRR) array and a polyimide (PI) kirigami sheet, using a standard horn antenna as the transceiver antenna to communicate with the resonator array. Nonlinear finite element analysis is performed on the kirigami structure to predict the mechanical responses of various kirigami designs and obtain the stress distribution on the kirigami structure surface after stretching. The electromagnetic simulation and circuit simulation of the designed element structure are carried out, verifying the validity of the equivalent circuit model and the consistency of unit performance by comparing the simulation results. The resonator array is mounted on a custom kirigami sheet, where under quasi-axial stress, the kirigami design enables each resonant unit to shift and flip, thereby altering the overall electromagnetic properties of the surface. Experimental results show that when tensile force is applied to increase the strain level of the kirigami structure from 0% to 18%, the sensor exhibits a resonant frequency shift exceeding 30 MHz and a resonant amplitude shift exceeding 40 dB, with a sensitivity of 1.928 MHz/%. Additionally, the reflection coefficient changes by 172% within the strain range of 0%–8%. Compared with traditional strain sensors, this sensor has achieved noncontact and accurate strain measurement, expanding the application potential of strain sensors in monitoring structural deformation within complex engineering environments.

This paper presents a W-band broadband low-noise amplifier (LNA) implemented in a 100-nm GaAs process. A key innovation of the design is the co-optimization of gain peaking and staged source degeneration, which together enable flat gain and broadband noise performance. The work begins with an analysis of pseudomorphic high-electron-mobility transistor noise behavior, identifying the optimal noise current density as a critical design parameter. By selecting appropriate device dimensions and biasing the transistor at this current density, the noise is minimized theoretically. A four-stage cascaded topology is adopted, in which each stage applies tailored source degeneration feedback and interstage microstrip lines are optimized for broadband matching. Measurement results demonstrate a minimum noise figure of 4.4 dB across 75–90 GHz, with 17.5–20.5 dB gain, 3 dB gain flatness, input and output return losses below 5.9 and 6 dB, respectively, and isolation better than 38 dB, achieving state-of-the-art performance in the W-band.

A millimeter-wave (MMW) voltage-controlled oscillator (VCO) with parallel feedback architecture is proposed in this paper. A diplexer with large frequency ratio is exploited to act as a fundamental frequency stabilization and third-harmonic frequency extraction component, simultaneously. It consists of an X-band microstrip bandpass filter (BPF) and a Ka-band substrate integrated waveguide (SIW) BPF. The characteristics of the proposed diplexer possess a decent performance of high isolation between the two output ports. To verify the proposed architecture, a Ka-band VCO prototype is designed, fabricated, and measured. The observed outcomes indicate that the frequency tuning range is from 26.19 to 26.76 GHz, and the designed VCO achieves a superior phase noise (PN) of −128.7 dBc/Hz and the corresponding figure of merit (FOM) indicates −203.8 dB/Hz at 1-MHz offset frequency.

This article proposes a wideband bandpass filter (BPF) based on modified T-shaped resonators (MTSR) for 5G mid-band communication. The proposed BPF uses a T-shaped resonator connected to a J-inverter structure. This approach significantly reduces the filter size. In contrast to conventional wideband filters, this design prioritizes high selectivity and minimal insertion loss, which are essential for effective 5G communication. The length and width of the resonators can be optimized to observe the passband responses. The filter is fabricated on Roger4003 substrate with relative permittivity ε_r = 3.55, thickness 0.508 mm. The resulting band is centered at 6.25 GHz with fractional band widths of 65.6%, ranging from 4.2 to 8.3 GHz. The simulation was carried out using HFSS. The filter provides good passband performances, with IL < 0.2 dB and RL > 10 dB. The research suggests that this filter design can be crucial in advancing dependable and efficient 5 G communication networks, addressing the increasing need for rapid data transmission and connectivity.

In this letter, a low scattering ultrawideband tightly coupled dipole array (TCDA) based on the wideband absorber is proposed in this paper. The absorber consists of I-shaped metal strips loaded with resistors. Transverse metal strips are attached at both ends of the vertical strips to enhance the capacitive coupling between neighboring I-shaped strips, resulting in a broader low-frequency absorption bandwidth. The feeding networks and wide-angle impedance matching (WAIM) layers are meticulously designed to achieve optimal impedance matching and scanning performance. A 10×10 array prototype is fabricated and measured. Simulation and experimental results show that the designed array achieves 108.6% relative bandwidth of at least 10 dB scattering cross section reduction, demonstrating improvement over existing solutions. The array can scan up to 70° in the E-plane and 60° in the H-plane for voltage standing wave ratio (VSWR) < 3.5, exhibiting high potential for large beam scanning.

This letter presents an efficient modeling and fast simulation method for varactor diodes. By analyzing varactor diodes' circuit characteristics, the equivalent current density of varactor diodes is extracted to obtain an efficient Yee modeling. This modeling can realize the conversion between field and circuit. Besides, the efficient modeling is introduced in the leapfrog complying divergence implicit (LCDI) finite-difference time-domain (FDTD) method for rapid analysis of varactor diodes. Finally, the typical electromagnetic (EM) devices with varactor diodes are calculated. As demonstrated by the comparison of numerical results, the proposed method exhibits higher computational efficiency in comparison with the traditional FDTD method. Furthermore, in comparison with the leapfrog alternating direction implicit (LADI) FDTD method, it demonstrates lower storage requirements and smaller numerical errors. The proposed method supports the design and analysis of EM tunable devices employing varactor diodes.

In this study, an analysis is conducted on the strong reflection points (SRPs) of a serpentine micro-rectangular-coaxial delay line (MRCDL), to reveal the origin. It is disclosed that the SRPs are caused by the residual crosstalk at the bends between the adjacent segmental lines. The SRPs still exist and are stronger in the higher frequency band, and the periodicity is still related to the electrical length of the segmental lines, as in the conventional microstrip delay line. Even though the coupling strength between the adjacent segment lines in the MRCDL is greatly weakened comparing to the conventional serpentine microstrip delay line. The analysis gives us a caution that the SRPs are still needed to be avoided in the design of the MRCDL, which can be realized by adjusting the delay line pattern.