Microwave and Optical Technology Letters最新文献

In this letter, an electromagnetic stealth composite superlattice-type structure based on indium tin oxides (ITO) resistive film and frequency selective absorber (FSA) is proposed for radar cross section (RCS) reduction. It exhibits impressive ultra-wideband performance with absorption of more than 85% (RCS reduction 8.2 dB) spanning from 0.94 to 23.2 GHz (relative bandwidth 184.8%). The proposed absorber is also polarization-insensitive and has angular incidence stability up to 45° and 60° for TE and TM polarizations, respectively. Additionally, it demonstrates excellent miniaturization characteristics, with a cell size of only 0.15λ_L × 0.15λ_L × 0.09λ_L, which provides a technical solution for research and application in related fields.

This paper presents a novel single-pole double-throw (SPDT) mechanical switch using gap waveguide (GWG) technology. The design is based on the fact that no electrical connection between the upper and lower plates of GWGs is required. The proposed switch structure comprises two distinct components: the first is a fixed waveguiding section, while the second is a movable section used to switch between ports. Although the proposed method is general, for demonstration purposes, an SPDT switch for Ku-band applications is designed, fabricated, and experimentally characterized. The switch is fabricated by soldering pin headers on printed circuit boards (PCBs). The simulation and measurement results demonstrate that the proposed switch exhibits superior performance characteristics compared to other recently published GWG switches. The operating bandwidth, isolation, minimal signal attenuation, and robust power handling capabilities achieved make this switch highly attractive for operation in demanding communication systems.

A narrowband bandpass filter (BPF) using mixed lumped and distributed circuits is proposed with wide stopband and small circuit size. By loading four lumped capacitors on the two pairs of coupled lines and two open stubs, the periodic harmonics generated by the coupled lines and open stubs can be effectively suppressed, resulting in the achievement of wideband stopband. To validate the design, a narrowband BPF prototype with center frequency f₀ at 1 GHz is fabricated, whose measured 3-dB fractional bandwidth is 5% (0.97–1.02 GHz). The in-band insertion loss is less than 1.5 dB and return loss is greater than 32 dB. The rejection level of stopband is better than −20 dB at the frequency range from 1.05 to 6.22 GHz.

In this paper, the idea of cross-coupling is applied to realize zero-controllable high-selectivity band-pass frequency selective surface(FSS). The element consists of two resonant layers at the top and bottom and a coupling layer in the middle. Cross-coupling is introduced into the structure, which makes it have electric coupling, magnetic coupling and direct path. Two transmission zeros(TZs) are generated on both sides of the passband, thus realizing the filtering characteristics of fast roll-off. The mechanism of TZs generation is studied by using an equivalent circuit odd-even mode analytical method. Due to its centrosymmetric structure, the FSS has good angular stability and polarization stability. FSS samples with operating frequency at 19.25 GHz, low stop band at 18.2 GHz, and high stop band at 20.8 GHz were fabricated and tested experimentally. The FSS maintains stable performance at an incidence Angle of 75°. The measurement results are in good agreement with the full-wave and circuit simulation results, verifying the design of FSS.

In this paper, a novel technique for the design of microstrip tight-coupling directional coupler with node-segment-type structure (NSTS) is proposed. The NSTS is configured by connecting microstrip line segments among free nodes distributed on the print circuit board (PCB). L-shaped line segments characterized by constraint nodes and individual width are proposed for detailed geometry description of NSTS. The optimal NSTS can be acquired by implementing multiobjective optimization search for the optimal distribution of the nodes and the line widths. For demonstration, a 3-dB microstrip directional coupler working at 1.75 GHz is designed with NSTS in a compact size. The measurement indicates that high directivity over 36 dB and amplitude imbalance of < ±1 dB in an operation bandwidth of 33% can be obtained.

A wideband differentially fed rectangular dielectric resonator antenna (DRA) is investigated in this paper. The proposed DRA is based on a wideband balanced-to-balanced microstrip-to-slotline power divider (MSPD). The balanced MSPD is designed using the multi-mode resonance of a slotline which realizes a broad 10-dB differential impedance bandwidth of 87% (1.84–4.45 GHz). The rectangular DRA can be excited to operate in a wideband TE₁₁₁ mode. The DRA has a 10-dB differential impedance bandwidth of about 42.6% (2.48–3.74 GHz) and a broadside radiation pattern with a peak gain of 5.2 dBi. The proposed differential-to-differential feeding mechanism to excite DRA can perfectly match with wideband differential circuits.

A surface plasmon-polariton graphene waveguide directional couplers for THz region are discussed in this paper. The device has a very simple structure. The central part of it presents two side-coupled parallel graphene nanoribbons with a small gap between them. The graphene waveguides are deposited on a dielectric substrate. In one of the presented examples, the proposed 3 dB coupler has a 25% fractional bandwidth centered at 3.8 THz with isolation and return losses better than −17 dB. By changing the Fermi energy of graphene, the power division in a given frequency range can be dynamically controlled or, alternatively, a frequency band of the coupler with a fixed power division can be dislocated. The discussion is fulfilled in terms of the so-called frequency reference point corresponding to a 3-dB coupler. We determine also the limits of possible coupler parameters tuning in the frequency range from 2 to 8 THz. The suggested general analysis can be useful in the design of graphene couplers for high-density integrated THz circuit.

In this work, a three-stage ultra-wideband and high-efficiency monolithic microwave integrated circuit (MMIC) power amplifier (PA) from 17 to 41 GHz has been designed and realized. The available bandwidth, efficiency, output power, and drain voltage of the transistor have been thoroughly considered during the PA design. Additionally, the gate peripheries of the driving stage ratio are set as 1:1.5 to prevent premature saturation of the driving stage. Pulse measurements show that the PA has a saturated output power greater than 1.2 W across 83% of the fractional bandwidth (FBW). The power gain is over 15 dB with less than 1 dB variation, and it reaches a peak output power and PAE of 32.5 dBm and 33%, respectively. This PA presents notable wideband performance and advantages in comparison with other PAs in previous works.

In this letter, a tri-band on-body/off-body wearable substrate integrated waveguide (SIW) textile antenna operating in the World Interoperability for Microwave Access (WiMAX) band (2.3–2.69 GHz; 3.3–3.8 GHz) and WLAN band (5.15–5.825 GHz) is proposed. The antenna uses a SIW resonant cavity, which allows multiple frequency points to be excited to achieve multi-frequency characteristics, and a layer of metasurface (MS) structure is added to adjust the resonant frequency points and impedance bandwidth. The final results show that the antenna performance is good, the measured results are consistent with the simulated results, the peak gain is 9.27 dBi, the antenna creates the omnidirectional and unidirectional radiation patterns very well, in addition, its wearable performance is good, in the human body and the free space measured data is basically the same, using the three-layer human body tissue model to calculate the antenna's Specific Absorption Rate (SAR) value, and the calculation result is lower than the upper limit of the United States and the European Union standards, These characteristics indicate that the antenna can be used in wearable systems.

In this letter, a dual-polarized dipole antenna with wide beamwidth in both E-plane and H-plane is developed. Compared to the typical printed dipole antenna, the radiator arms of the developed dipole antenna are bent into arc shapes to broaden the beamwidth. Moreover, four short arc-shaped metallic patches, which act as directors, are introduced to the outside of each radiator arm to further broaden the beamwidth. Simulated results show that the developed antenna achieves an operational bandwidth (where the value of reflection coefficients is less than −10 dB) of ~14.7% (1.76–2.04 GHz). In addition, the half-power beamwidths in both the E-plane and H-plane of the developed antenna are significantly broadened throughout the operating frequency band compared to the reference printed dipole. Specially, the beamwidths enhanced from 58° to 135° in the E-plane and from 95° to 128° in the H-plane, which validated the effectiveness of the developed beamwidth enhancement method. A prototype is fabricated and measured and shows good agreement with the simulated results.