Microwave and Optical Technology Letters最新文献

Based on the improved YOLOv8n, a steel plate defect detection and recognition method is proposed to address the high labor costs and workload of traditional tasks. SPPFELAN processes inputs in parallel to enhance computational efficiency by executing multiple pooling operations simultaneously. The parallel feature fusion module PscSE, using a mixed-dimension SE attention mechanism (scSE), captures global and channel-related information better, improving characterization capability. The EIOU loss function addresses the ambiguous aspect ratio definition of CIOU loss, enhancing detection accuracy and accelerating convergence. Results show the YOLOv8n-PscSE-SPPFELAN model achieves 76.9% [email protected] on the Northeastern University steel plate dataset, a 4.6% improvement over the original YOLOv8n, with a computation amount of 7.7 GFLOPs, reducing resource usage and greatly improving detection speed.

Microstrip antennas are increasingly utilized in space-borne applications, spanning areas such as RFID, mobile communication, and healthcare. This paper introduces a novel wearable ultra-wideband (UWB) microstrip patch antenna, distinctively designed in a star shape. The antenna, with a total volume of 1172 mmÂş, is crafted on a semiflexible substrate using RT/duroid 5880. It exhibits a low loss tangent of 0.0004 and a relative permittivity of 2.2. The proposed design achieves a resonant frequency of 3.4 GHz, an impressive reflection coefficient of −39 dB, and an extensive bandwidth of 5.6 GHz, ranging from 2.8 to 8.4 GHz. Although the antenna demonstrates modest gain and directivity, its expansive bandwidth is a significant attribute. This wideband antenna is proposed as an ideal candidate for wearable biomedical applications, leveraging its substantial bandwidth and unique design characteristics.

A common design solution of wideband filtering antennas inspired by the synthesis of a flat-top gain curve is proposed by using mutual coupling effects. The realization of a frequency-varied flat-top gain curve based on specially designed subarrays is analyzed. Analysis results conclude a design process of generating filtering response based on shorting pins and parasitic structures. A single-layer rectangle patch array loaded with parasitic shorted patches is designed and analyzed for the validation. The proposed antenna possesses an impedance bandwidth of 4.95–6.05 GHz and a peak realized gain of 11.2 dBi. Besides, the design has its out-of-band rejection levels higher than 15 dB.

In this paper, an enhancement gain of compact CPW-Fed antenna using a single layer frequency selective surfaces (FSSs) reflector for ultra-wideband (UWB) applications is presented. A hexagonal CPW-Fed antenna with a size of 30 × 30 mm² is realized to provide a UWB bandwidth operation. In this study, a novel design of an FSS unit cell with reduction and a small size of 8 × 8 mm² is proposed. It allows one to achieve a UWB band-stop response between 3 and 11.5 GHz. The FSS reflector has 7 × 7 units with a total size of 56 × 56 mm². This reflector is placed below the antenna at a distance of 20 mm. The main objective of this contribution is to improve the gain level of the antenna, where the proposed antenna achieves an improvement of realized gain of 6.2 dBi with increasing from 2.2 to 8.4 dBi. The antenna became more directive after the integration of the FSS reflector with a directional radiation pattern. The numerical and experimental results are in good concordance with the simulated one. This study is performed in terms of voltage standing wave ratio, radiation pattern, realized gain, and radiation efficiency.

This paper presents a novel additively manufactured wideband dual circularly polarized (CP) open-ended waveguide (OEW) antenna, which adopts a pair of wedge-shaped outer ridges acting as a circular polarizer. Study found that compared to the con- ventional designs that employ internal polarization converting structures, such outer ridges are capable of achieving wider axial ratio bandwidth (ARBW) and better reflection coefficients. On each ridge, two rectangular slots are designed to suppress the higher order mode caused by the increased waveguide size, and further expanding the ARBW. The proposed antenna is fed by two differential ports. By switching the feeding ports, the CP states can be altered to either right-handed CP (RHCP) or left-handed CP (LHCP). In terms of configuration, the proposed antenna has a simple one-piece structure and is fabricated by using dielec- tric 3-D printing technology. To form the waveguide walls, its partial surfaces are coated by copper films through electroplat- ing. The proposed antenna features easy fabrication and light weight. Experimental results show that the proposed antenna has an impedance bandwidth of larger than 47.6% (8–13 GHz) with reflection coefficients lower than −15 dB, while the 3-dB ARBW is 37.7% from 8.4 to 12.3 GHz.

A folded transmitarray antenna (FTA) with low profile, high efficiency, and broadband is proposed. The transmission unit-cell is composed of two metallic layers of bowknot-shaped patches printed on a single layer of dielectric substrate. By regulating bowknot-shaped patches' dimension and mirroring elements' top and bottom layers, 360° phase swing and high transmission magnitudes are obtained. With the introduction of a reflectarray integrated with a feed horn in the middle, an FTA is designed based on ray tracing principle, leading to a profile reduced to 1/3 of the focal distance of traditional transmitarrays. According to testing results, 15.5% 1 dB gain bandwidth, 30.9% 3 dB gain bandwidth, and 42.3% peak aperture efficiency are achieved. These outstanding performances demonstrate its good potential for a wide range of high-gain applications.

This letter introduces a novel design approach for broadband radar cross section (RCS) reduction of frequency selective surface (FSS) radomes. The approach integrates the principles of phase cancellation and spatial filtering together through a hybrid design method. The phase cancellation is obtained through the checkerboard arrangement of units, and the spatial filtering characteristics is achieved by the slot etched on the ground plane. Experimental and simulation results demonstrate that etching slots on the ground plane maintains broadband in-phase reflection and bandpass characteristics, thereby extending the bandwidth of RCS reduction through a combination of two operation bands. Theoretical analysis of the working mechanism is also provided using equivalent circuit models. In comparison to the conventional radomes, the proposed FSS radome achieves significant bandwidth improvement for RCS reduction, indicating that it has promising prospects in future low-RCS radome applications.

Pathology is an important branch of science in the diagnosis and treatment of several diseases. In cancer diseases, serious investigations have been made about the course of the diseases. A report that is essential for both the patient and the doctor is prepared by the pathologists as a result of a detailed cellular examination. These reports contain information about the disease. Access duration to these reports, which affects the form and duration of the treatment, is extremely important today. It is possible to shorten this period with systems using antenna technologies. The pathological breast tissue samples have been examined by using horn antenna structures with high gain in this study. Dual identical horn antennas have been placed opposite each other as receivers and transmitters in the measurement setup at 24 GHz. Measurements of normal and cancerous breast tissues have been made, and the normalization process has been applied to the measured scattering parameters. The different values between normal and cancerous breast tissues have been shown with this process. The normalized values are compared with other analyzed values. According to the results obtained, the percentage of normalized values for transmission is much more effective and meaningful than other results.

This letter explores the possibility of long-distance transmission of an orbital angular momentum (OAM) beam through rectangular tunnels. Theoretical analysis reveals that the OAM beam propagating in the tunnel with square cross section fulfills the conditions for axial propagation and exhibits azimuth symmetry. In comparison with free-space OAM generation, we draw the conclusion that long-distance transmission of OAM beams is achievable in the tunnels with square cross section. The validity of our conclusion is further substantiated through numerical experiments. Simulation results demonstrate that the first-order OAM beam radiated by a uniform circular antenna array exhibits favorable helical phase distribution and the circular symmetry of the amplitude distribution in the tunnel beyond the Rayleigh distance. However, these characteristics degrade with increasing mode order and propagation distance, because the increase of high-order OAM beam divergence angle and propagation distance will exacerbate the impact of multipath effects in the tunnel environment.

A fully integrated gallium arsenide (GaAs) heterojunction bipolar transistor (HBT) power amplifier (PA) for wireless local area network 802.11ax applications is presented in this paper. The structure consists of two-stage power cells. To satisfy the high linearity requirements of IEEE 802.11ax, we analyzed the distortion of amplitude-to-amplitude and amplitude-to-phase. Due to the thermal and voltage sensitivity of GaAs HBT, an adaptive bias circuit is designed to ensure linearity. Moreover, an efficient passive output matching network is designed by analyzing the efficiency of the passive network. The design electromagnetic structure is fabricated in a 2-μm GaAs HBT process. Under continuous wave testing, the output power reaches 27.2 dBm and the maximum efficiency of 28% at 2.4 GHz. Under the excitation of a 40 MHz 1024-quadratic amplitude modulation signal, the output power meeting error vector magnitude of −35 dB reaches 16.8–17.2 dBm from 2.4 to 2.5 GHz.