Microwave and Optical Technology Letters最新文献

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.

An ultra-wideband antenna with solar cells is presented for low-carbon wireless communication. Four solar cells are introduced for the radiation structure with a solar cell coverage of 80.9%. A foam substrate with a low permittivity is adopted for lightweight and wideband characteristics. Different resonant modes are stimulated for wideband performance based on the slot and patch structures. The measured results show that the working frequency band (|S11| < −10 dB) is from 1.42 to 5.3 GHz with a relative bandwidth of 115%. Bidirectional radiation patterns are achieved across the passband with an average gain of 4.5 dBi. This ultra-wideband dual-function design has a lightweight and planar structure for easy installation. It can accommodate various wireless communication systems (2G, 3G, 4G, and 5G) with the capacity to power self-supply.

Accurate phase distribution and excitation incident characteristics are key issues in the design of conformal metasurface array antenna (CMAA). In this paper, we employ the improved conformal phase compensation formula to calculate the accurate phase distribution at different bending degrees. Meanwhile, elements with stable incident characteristics are designed to minimize the phase-shift deviation caused by the increase in incident angle. Furthermore, the combination of 1Bit digital coding and superposition of aperture fields enables the CMAA to adapt to different bending degrees while realizing beam-forming. Based on the designed structure, a 10 GHz dual-beam in the direction of (φ = 90°, θ = ±45°) conformal reflect-array antenna (CRAA) is fabricated by printing 15 × 15 liquid metal elements on PDMS substrate. The measured peak gain is 17.9 dBi, and the antenna maintains favorable radiation characteristics in the range of bending degree between ± 25%.

This paper proposed a SIGW wideband 3-dB coupler that operates mainly in the Ka-band by combining the SIGW theory and the theory of branch-line coupler. Firstly, the structure of the SIGW is analyzed. Then, the coupler is designed using the SIGW transmission line with five-branch to realize a wideband. Finally, the proposed SIGW coupler is fabricated and measured, and the measurement results are consistent with the simulation results. The SIGW coupler centered at 30 GHz has a 40% wide bandwidth (24–36 GHz). The return loss of the coupler is better than 10 dB and the isolation is better than 17 dB. The SIGW coupler in this paper has a wide operating bandwidth, high isolation, and is easy to fabricate compared to conventional branch-line couplers.

This article presents a design method for compact and continuously tunable 360° phase shifter (PS). The proposed structure consists of a 180° reflection-type phase shifter (RTPS) cascaded with a 180° switched-type phase shifter (STPS). RTPS consists of a transformer-based 90° coupler and Γ-π reflection loads. STPS consists of a transformer and a single-pole double-throw (SPDT). For experimental verification, a compact and continuously tunable 360° PS with a center frequency of 1.5 GHz was designed and fabricated. From the measurement results, the proposed 360° PS provides a tunable phase shift range (PSR) of 0°–360°, with an the insertion loss (IL) of 2.85 ± 0.7 dB, which has a circuit size of 0.031 λg².