Microwave and Optical Technology Letters最新文献

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.

A compact two-dimensional beamforming system for sub-6 GHz applications is presented, combining a Butler matrix with a four-element reconfigurable antenna array. Each antenna element consists of a rectangular patch and two metallic strips reconfigured by PIN diodes. The patch radiates in the broadside direction, while the reconfigurable strips help to steer the beam in two additional directions. When the PIN diode is ON, the strip acts as a reflector; when OFF, it behaves as a director, enabling dynamic beam control. The system generates 12 distinct beams by varying the diode states and input ports of the Butler matrix. It achieves a wide beam tilt range from −60° to +66° and a peak realized gain of 9.79 dBi. The proposed design offers a compact, low-profile solution for enhanced beam steering, suitable for next-generation wireless systems requiring high directionality and adaptability.

An efficient dual band transmission metasurface capable of generating OAM beams of different orders in the K-band and Ka-band is designed. The proposed metasurface unit consists of an intermediate dielectric substrate layer and two metal resonators for top and bottom layers. By adjusting the rotation angles of different resonators, the circularly polarized transmission phase at the K-band and Ka-band can be controlled independently, with both transmission coefficients larger than 0.8. By using this unit, a metasurface array that generates + 1 order OAM beam at the K-band and + 2 order OAM beam at the Ka-band is realized. Experimental results show that the generated OAM beams exhibit excellent performance, with measured main mode purity at the these two test frequencies is 0.71 and 0.7, respectively. This study provides a solution for generating multi-band OAM beams.