International Journal of RF and Microwave Computer-Aided Engineering最新文献

In this paper, deep learning–based data-driven surrogate modeling approach is proposed for enhancing cost-efficiency of multiband antenna design optimization. The proposed surrogate model–assisted design approach has achieved a computational cost reduction of almost 40% compared to the conventional direct electromagnetic solver–based design methodologies in case of single design example. As for the validation of the proposed method, the obtained optimal design parameters from the surrogate model are used to manufacture an antenna design. The obtained results from the experimental measurement are compared with counterpart results from the literature.

A novel and simple design method of wide-passband filters with wide stopband based on half-wavelength (λ/2) resonators coupled by a short connected line (SCL) is proposed and analysed in this paper. Different from the traditional parallel-coupled structure filters, SCL is proposed to realize a strong coupling between two adjacent resonators and suppress the parasitic passbands simultaneously. And the eigenmode analysis method and impedance ratio characteristics are both used to reveal the mechanism of wide-stopband implementation. To further expand the stopband, filters based on step-impedance resonators (SIRs) with SCL are proposed and analysed in detail. To verify the proposed design method and wide-stopband filtering structures, three 4-pole filters with uniform-impedance resonators (UIRs), SIRs with same impedance ratio, and SIRs with different impedance ratios are designed, fabricated, and measured. The proposed filters can realize a wide stopband up to 5.8f₀ with rejection level better than 20 dB. Moreover, the proposed filters can easily realize a wide bandwidth.

Passive millimeter–wave (PMMW) scanners are widely used for personal security screening in public places due to their nonradiation and high real-time capabilities. However, the images obtained by these scanners frequently exhibit low signal-to-noise ratios and contrast, presenting challenges for automated detection systems. To address this issue, we propose an efficient semantic segmentation approach, FA-UNet, that employs a UNet architecture with a fusion attention mechanism to conduct binary classification (human body vs. background, including objects) for PMMW images. This approach incorporates a spatial attention mechanism into the lateral connections between the encoder and decoder and introduces a channel attention mechanism during the feature fusion process in the decoder. By combining these attention mechanisms, FA-UNet leads to more precise segmentation outcomes. The segmented image is then fused with the original image using our multistage fusion method, in which, first, the two images are blended in a 1:1 ratio for object detection. Then, a new fused image is obtained by adjusting the ratio within a certain range (0.3–0.5). Finally, the object detection results are overlaid on this fused image to generate a directly displayable image. We evaluate our method using a self-made dataset. Experimental results demonstrate that FA-UNet can accurately segment the human body region and preserve object shapes effectively. Using the fused image for object detection helps reduce false detections caused by background noise interference while improving the detection rate of weak targets. Additionally, the fused image aids in manual image interpretation in locations with higher security inspection levels and contributes to protect the privacy of individuals undergoing inspection to the greatest extent possible.

A small antenna is critical in wireless communication and monitoring of vital signs using data collected by implantable devices. Numerous studies address antenna miniaturization and reliability challenges while maintaining performance efficiency in this field. A reliable small-sized circularly polarized antenna of dimension (4.15² π × 1.28) mm³ developed for medical implants operating at the 1.4-GHz Wireless Medical Telemetry Service (WMTS) narrow band is presented in this work. The shorting pin, variable arc slots, and substrate and superstrate of high dielectric constant techniques were used. The proposed antenna underwent testing in a three-layer biological simulation environment that includes the skin, fat, and muscle. Subsequently, the antenna was fabricated, and measurements were performed by placing the antenna in beef biological tissues. The measurement results confirmed the simulated results. The antenna achieves an impedance bandwidth of 98 MHz (1.367~1.465 GHz, 7%). The effective axial ratio bandwidth (AR <3 dB) is 55.2 MHz (1.3668~1.422 GHz, 3.94%), which covers the CP operating frequency range. The simulation results attain a peak realized gain of −19.2 dBic. The communication link budget and the specific absorption rate (SAR) were analyzed. The results indicate that the radiation of the proposed antenna aligns with the safety limit of IEEE C95.1-1999 standards. The antenna exhibits excellent performance and reliability compared to other works operating within the 1.4-GHz WMTS band.

Microwave ablation (MWA) is based on the energy absorbed by biological tissue through microwave emission, which raises the temperature of the tumor to perform the treatment. MWA has the advantage of causing minimal bleeding and treating deep tumors. In this study, MWA for various slot design situations in a microwave coaxial antenna (MCA) was simulated through numerical analysis. For the slot design, the number of slots and the distance between slots were determined by the analysis parameters. A tumor developed inside the liver tissue was implemented, and the temperature distribution of the tumor and surrounding liver tissue was calculated for all cases selected for numerical analysis. The Helmholtz electromagnetic equation was used to calculate the electromagnetic field inside the tissue, and the modified Pennes bioheat equation was used to calculate the temperature change in the tissue due to the emitted microwave. Treatment effects were quantitatively analyzed for each slot design condition through an apoptotic variable based on the calculated temperature distribution. Lastly, conditions that produce optimal treatment effects were derived depending on the number of slots. The analysis showed that as the distance between the slots increased from 0.5 to 3.5 mm, the optimal treatment effect was obtained when the number of slots was 4, 3, 3, and 2, respectively, and the microwave input power at that time was 3.0, 2.8, 2.6, and 3.0 W, respectively. This is expected to allow for more rigorous and more therapeutically effective MWA.

In China, high-speed trains have become a major means of transportation for the masses. When the passengers wearing pacemakers travel on high-speed trains, electromagnetic environment in the carriage where the GSM-R voice and data antennae are located should be concerned. In this work, a real-size carriage monopole antennae simulating voice and data antennae as high-frequency radiation sources and wearing pacemaker passenger’ models were established to study the electromagnetic exposure of the passenger at different conditions. The results showed that when the passenger faced the voice antenna, he suffered much greater electromagnetic radiation than when his back in turned from it. The electric field strength, average SAR, and temperature rise of the heart when facing the antenna were 27.3 V/m, 0.0102 W/kg, and 0.0016°C, respectively. Meanwhile, the temperature rise of the pacemaker was 0.001°C. We also obtained the values of electromagnetic dose for the whole body. All data were below the limits of the ICNIRP guidelines. These results indicate that the electromagnetic fields generated by the GSM-R voice and data antennae do not harm the health of passengers wearing pacemaker.

This paper proposes and analyzes a 2 × 2 multi-input multioutput antenna based on an open-loop resonator structure and an inverted L structure. The top layer of the antenna uses symmetric inverted hook-shaped and inverted L branches and is connected to the bottom layer of the dual-feed port and the ground plane using the VIAs, respectively. The open-loop resonator structure at the bottom of the antenna and the top layer of the branched circuit are resonated to provide wide-bandwidth and dual-frequency characteristics. The substrate uses FR4 with an area of 40 × 30 × 0.8 mm³. Although the two antenna feed ports are very close to each other, using via to connect the defective bottom ground structure and the top inverted L-shaped branch, the isolation still achieves an excellent performance of 15 dB. The antenna has multiband application characteristics, and the bands include 2.29–5.51, 6.14–10.26, 2.29–5.33, 5.19–6.64, and 6.78–10.16 GHz. In pattern and MIMO transmission efficiency measurement, the peak radiation efficiency is 89%, the peak gain is 8.5 dBi, and the ECC is less than 0.034. In the transmission efficiency measurement mode using 64-QAM, watching the error vector magnitude at 2.56 and 5.11 GHz, the demodulation effect is very good, and the respective throughput results are 100% and 79.2%. The broadband characteristics of the antenna have a variety of applications, and it is simulated at the specific absorption rate, which meets the standards set by the Federal Communications Commission and is very suitable for use in wearable devices. The antenna can be applied to the X-band, n77, n79, Sub-6 GHz, WiMax, DSRC, WiFi 6, WiFi 6E, WiFi 7, C-V2X, and C-band.

A multifunctional frequency-selective rasorber (MFSR) with passband stealth performance by using PIN diodes is investigated, which is made up of two reconfigurable components (a lossy layer and transmissive polarization converter surface (lossless layer)). The proposed MFSR shows transmission in-band and absorption out-band at working state, but the transparent window is closed to achieve full-band stealth at nonworking state. Besides, the equivalent circuit model (ECM) is constructed to annotate the operating principle of the designed MFSR. The MFSR indicates a wide cross-polarized transmission window from 3.71 to 4.38 GHz between two absorption bands at working, meanwhile a broadband copolarized reflection band (S₁₁ < −10 dB) is accomplished in 1.78–5.50 GHz. At nonworking, an ultra-wideband stealth band is realized in 1.81–7.0 GHz when the absorptivity is over 80%, which has a 117.8% fractional bandwidth (FBW). In addition, the MFSR has a stable oblique incident characteristic (up to 25°). Finally, the sample of the MFSR is manufactured and experimented to demonstrate the availability of this design.

In this article, distance and frequency-dependent indoor wireless channel characterization and modeling are presented in C, X, and Ku bands at the line of sight (LOS) and nonline of sight (nLOS) scenarios. Complex frequency responses of the indoor radio channel are measured using the frequency-domain approach. The terminal and measurement setup dependencies of the propagation channel are deconvoluted using closed-form expressions devised from a two-port network model approach of the antenna transreceiver system. Subsequently, terminal independent frequency-domain channel transfer functions (CTFs) and time-domain channel impulse responses (CIRs) are derived for accurate statistical analysis of large- and small-scale fading parameters of the propagation channel. A distance-dependent statistical pathloss model is proposed. Successively, a frequency domain channel model using the fifth-order autoregressive process is proposed. Subsequently, the existence of the multiple clusters in the environment is analyzed by the poles of the transfer functions of the model. Models are validated in both time and frequency domains by comparing the computer-simulated synthetic model data with the empirical channel responses. The measurement data and the model data are seen to be in good agreement.

This paper proposes a 10 × 10 MIMO multiband broadband planar antenna for tablets or laptops. The designed antennas cover a large number of the popular sub-6-GHz application bands, such as 0.617–0.96, 2.1–2.7, 3.5–4.5, and 6.1–7.2 GHz for public safety communications, radio systems, Bluetooth, Wi-Fi, and satellite communications. The proposed antenna is designed with grounded branches, which can generate a wide bandwidth and cover most of the sub-6-GHz application band by coupling between branches of different lengths and antennas. MIMO antennas have been measured to have an envelope correlation coefficient of less than 0.7 and have met the standards set by international organizations for human radiation absorption simulations. The proposed antenna validates the unique 10 × 10 MIMO antenna structure and feasibility. Multiple operable frequency bands are realized, and the radiation effect of the antenna on the human body is analyzed if it complies with international market standards. The proposed antenna design is well suited for multiband and broadband requirements.