International Journal of Rf and Microwave Computer-Aided Engineering

In wireless telecommunication systems, the precise adjustment of the antenna direction has a direct effect on the quality of the received signal. In this article, a new routing algorithm is designed using the wireless energy harvesting (WEH) technology from electromagnetic waves to adjust the orientation of the receiver antenna. The algorithm is simulated for routing in TDD LTE cellular network at 2.35 GHz frequency. The proposed antenna in this article is a cross‐dipole type with dual‐polarization RHCP and LHCP, and its measured impedance bandwidths are 1.97–2.70 GHz at Port 1 and 1.96–2.72 GHz at Port 2. Also, 7.45 dBic peak gain and end‐fire radiation capability of the proposed antenna are among the advantages of the automatic routing system. The proposed rectifier for WEH uses the voltage doubler technique. A new construction of microstrip elements has been used for the impedance matching network (IMN). The fabricated rectifier at 2.35 GHz can provide PCE = 52.8% at −0.5 dBm input power, which is suitable for WEH.

A printed MIMO antenna specifically designed for small satellite communication has been presented in this paper. The antenna is invented of two radiators resonating at millimeter-wave and constructed using Rogers’s RT duroid 5880. The design includes two identical octagonal patches with a diamond-shaped slot and having two quadrilateral notches. These elements are placed over a substrate and connected to a microstrip transmission line that embeds a quarter-wave transformer. To establish the effectiveness of the MIMO antenna being proposed, a comparative analysis is conducted between its simulated and experimental performance. Each radiator in the antenna setup includes partial ground, which forms the back layer of the substrate. The design is simulated on the CST tool, and measurements are conducted on a Rohde and Schwarz vector network analyzer. The obtained results show a favorable level of agreement with the simulated outcomes, validating the effectiveness of the proposed MIMO antenna. The antenna design offers exceptional features such as wide bandwidth, self-isolated, high gain, and a directional radiation pattern while also supporting a wide frequency band, making it an ideal choice for 28 GHz band applications. The performance of MIMO antennas in diversity can be determined using parameters such as envelope correlation coefficient (ECC), diversity gain (DG), and total active reflection coefficient (TARC). Satellite communication will be improved by implementing the suggested MIMO antenna through upgrading small satellite communication systems.

In the context of the rapid development of wireless body area network and ultra‐wideband technology, this design puts forward a new structure of ultra‐wideband flexible antenna. Its operating band is 1.22–8.82 GHz, with a maximum gain of 4.8 dBi. The antenna adopts a polyimide material with a relative dielectric constant of 3.5 and a thickness of 0.2 mm as the dielectric substrate. The overall size of the antenna is very small, measuring 0.15 λ × 0.21 λ at the lowest frequency of 1.22 GHz. In this paper, the influence of some antenna parameters on its performance, the influence of different bending conditions on the performance of the antenna, and the specific absorptivity of the antenna to the human body are discussed. In order to further explore the performance stability of the antenna, the performance of the antenna under right‐angle bending is simulated and tested in this paper. Simulation results show that the antenna still has two frequency bands 1.22–2.58 GHz and 3.35–9.53 GHz under right‐angle bending, which can still cover most of the commercial communication bands, and the measured results are in good agreement with the simulation results. Therefore, the antenna has strong adaptability and damage resistance and can be used in wearable equipment for military or emergency rescue.

In this letter, an ultrawideband stacked structure metasurface is designed to minimize the backward RCS across a frequency range of 5–40 GHz. The stack structure design demonstrated a maximum RCS reduction at 19 GHz, achieving an impressive reduction of 18.11 dBsm compared to a PEC of the same dimensions. The proposed metasurface exhibits the capability to scatter incident plane waves in various directions under both normal and oblique incidence conditions. Additionally, the calculated quantized encoding phase can facilitate further RCS reductions of 3–6 dBsm within the frequency range of 8–25 GHz. Consequently, this work effectively designs and promotes research on low RCS metasurfaces across different frequencies.

This paper presents an improved design of a Ku‐band power divider (PD) based on a substrate integrated waveguide (SIW) technology. The design is aimed at using the block upconverter (BUC) of the Ku‐band satellite communication system. The PD has been developed to operate in the frequency range of 13.75–14.5 GHz for low‐loss, good isolation, and good amplitude and phase imbalances for both power dividing and combining. To increase the isolation between output ports, TE 102 mode is selected to operate in the main cavity while the coupled cavity operates in the TE 101 mode. Low insertion loss of the PD can be achievable by determining Q factor of the SIW cavities. In addition, good phase and amplitude imbalances can also be obtained by making a suitable arrangement of the input and output ports. The measured results at the center frequency of 14.12 GHz exhibit an insertion loss of 1.3 dB, return loss of 16.9 dB, isolation of 16 dB, amplitude imbalance of 1.2 dB, and phase imbalance of 2.8°. The simulations are consistent with the measurements, validating the accuracy of the proposed method. The proposed PD can be a promising candidate for use in the BUC of the Ku‐band satellite systems.

In this work, we propose a physics-informed extreme learning machine (PIELM) method to identify the eigenmode field distributions of waveguides and transmission lines by solving Helmholtz partial differential equation (PDE) with initial and boundary conditions. A single-layer neural network architecture is adopted in PIELM, where the input layer parameters are initialized randomly. By embedding physics-informed constraints into the loss function, a system matrix equation can be established. Then, the output layer weights can be learned with the Moore–Penrose generalized inverse algorithm. Compared with physics-informed neural network (PINN), PIELM only uses a single-layer feedforward neural network and does not engage in an iterative optimization process utilizing backpropagation and gradient descent algorithms. As a result, the time spent on model training is reduced significantly, with the total process accelerated. Some numerical examples are presented to validate both accuracy and efficiency of PIELM method compared with PINN method in solving the eigenmode field distribution problem of waveguides and transmission lines.

This work presents a multiple-input/multiple-output (MIMO) antenna consisting of dipoles with integrated baluns and a parasitic element to reduce mutual coupling, which can cover two frequency bands. The configuration of the decoupling element is determined by using an optimization algorithm. The algorithm takes nine physical dimensions of the decoupling element as input and adjusts them by minimizing a cost function. One of these decision variables (DVs) is the number of decoupling element’s stairs (steps), which is a discrete parameter. In its simple form, the antenna cannot obtain proper isolation in the low-frequency band, which has been solved by employing a decoupling structure in the middle of the antenna. The experimental results show that the antenna has impedance bandwidths of 1.95–3.50 GHz and 3.98–5.67 GHz, providing minimum isolation of 13.1 and 19.5 dB in the low- and high-frequency bands, respectively. The ECC value is lower than 0.0038, and the peak gains are equal to 4.4 and 5.21 dB for the low- and high-frequency bands. The main contribution of this work is the design of the decoupling element, which, considering the antenna’s characteristics, has improved the antenna’s isolation by 12.4 dB only in the center of the low-frequency band.

In this paper, a compact dual‐band antenna module has been developed, achieving significant isolation between the ports. The design integrates an open‐edge slot antenna for the lower frequency band (5.15–7.1 GHz) with a 1 × 2 MIMO metasurface antenna for the mmWave frequency range (24.5–29.5 GHz), resulting in a high‐performance, compact dual‐band solution. The slot antenna is optimized for a reduced size configuration with enhanced bandwidth for lower frequencies, while the metasurface antenna delivers wider bandwidth and stable performance in the mmWave range with minimal mutual coupling and high efficiency. This makes the overall design highly effective for modern compact dual‐band applications. The dual‐band antenna module has dimensions of 20 × 16.5 × 0.99 mm (0.39 λ 0 × 0.32 λ 0 × 0.01 λ 0 , where λ 0 represents the free‐space wavelength at 5.85 GHz). It achieves a measured peak gain of 3.8 dB for the lower band and 8.81 dB for the mmWave band. Additionally, the output of the mmWave antennas can be combined for higher gain or used in a MIMO configuration, enhancing channel capacity and communication reliability, which are critical for modern wireless systems.

Aiming at the electromagnetic compatibility testing requirements of slender equipment, this paper proposes a design scheme for a cylindrical reverberation chamber. Through numerical simulation, the lowest usable frequency and field uniformity of the cylindrical reverberation chamber were analyzed. The results show that the cylindrical reverberation chamber has good field uniformity when the frequency is greater than 6fTE111, meeting the stringent requirements of IEC 61000-4-21. Utilizing this cylindrical structure for the reverberation chamber can effectively reduce testing costs and improve testing efficiency and accuracy. This research provides a foundation for further optimization of cylindrical reverberation chamber design, and it is expected to become an important tool for effective electromagnetic compatibility testing of equipment.

The domain decomposition method (DDM) enables efficient simulation of electromagnetic problems in large-scale array antennas using full-wave methods on moderate hardware. This paper introduces and compares two nonoverlapping DDMs serving as preconditioners with outstanding simulation efficiency. The first method targets finite periodic array antennas by transforming a single array unit rather than explicitly modeling the entire array, effectively leveraging repetitive structures to significantly reduce memory usage and computation time. The second method applies to universal array antennas with arbitrary geometries, employing both planar and nonplanar mesh-based domain partitioning at subdomain interfaces for flexible modeling of complex arrays. To further enhance computational performance, we propose a parallel multilevel preconditioner based on the block Jacobi preconditioner, thereby accelerating the solution efficiency of subdomain matrix equations in both methods. Additionally, since the choice of domain partitioning method significantly impacts the computational efficiency of DDMs, we propose three different subdomain partitioning strategies. These strategies enable us to accelerate computations while expanding our capacity to simulate a wider variety of types of cases. We developed a fast electromagnetic radiation simulation tool utilizing these techniques. Simulations of exponentially tapered slot (Vivaldi) antenna arrays and antenna arrays with radomes demonstrate that our tool achieves accuracy comparable to commercial software, and notably, our tool outperforms commercial software in terms of the speed of iterative solutions.

In this paper, a new coating structure is proposed for broadband radar cross section (RCS) reduction using 1-bit metasurfaces. The designed structure consists of two types of unit cell, arranged in concentric square rings. The substrate of unit cells is different, FR4 and Ultralum-2000 with thicknesses of 2.4 and 0.762 mm, respectively. The proposed structure shows an ultrawideband property to reduce the RCS, less than −10 dB, in the frequency range of 14–45 GHz. This range covers part of Ku-band (14–18 GHz), K-band (18–27 GHz), and Ka-band (27–40 GHz) and part of millimeter-wave band (40–45 GHz). To validate the designed work and simulation results, a prototype with the dimension of 84×84 mm² is fabricated and tested. Also, the RCS reduction is determined analytically and presented. The measured results verify well the analytical and simulation results. In short, this work includes three new points: (1) the use of two substrates with different thickness and dielectric constant to design unit cells, (2) a new arrangement of array cells in the form of concentric square rings, and (3) achieving a great bandwidth to reduce RCS.

The use of surrogate models in assisting evolutionary algorithms for antenna optimization has achieved significant research outcomes. The construction of surrogate model primarily depends on two aspects; one is the selection of datasets, and the other is the model’s structure and performance. This paper proposes a novel dataset selection method aimed at enhancing the performance of the constructed surrogate model. Additionally, based on Bayesian neural network (BNN) and leveraging the advantages of handling sequence data with long short-term memory (LSTM), a BNN-LSTM surrogate model is introduced. After training, this surrogate model is used as the fitness evaluation function, enabling optimization design based on differential evolution (DE) algorithm. Experimental validations are conducted using the optimizations of a dual-frequency slotted patch antenna and a rectangular cut-corner ultrawideband antenna as examples. Results demonstrate that the proposed surrogate model exhibits high accuracy, providing a guidance for antenna optimization.

A spaceborne Earth-coverage phased array (ECPA) antenna at Ka-band is proposed for low-Earth orbit (LEO) satellite applications, which is based on digital beamforming (DBF) partially shared subarray architecture to implement two stages of DBF. By taking into account the effects of mutual coupling in active element pattern optimization, a new method to obtain an Earth-matched beam of the equivalent element of the ECPA is presented, in which the DBF-shared subarray, segmental shaping technique, and differential evolution algorithm are utilized to achieve Earth-coverage characteristic for the ECPA. Both the design method and the principle of DBF partially shared subarray for grating lobe suppression are presented. Moreover, a 16-element DBF-shared subarray with a shared ratio of 4:1 obtaining an Earth-matched beam pattern is designed, optimized, and verified by full-wave simulation in Ansys Electronics Desktop. Taking the DBF-shared subarray as the equivalent element, an ECPA including 40 DBF-shared subarrays is also designed and simulated. Numerical results demonstrate that the proposed ECPA has excellent performance of Earth-coverage scanning to compensate for the satellite communication link variation caused by path loss variation during beam scanning for LEO applications. In addition, the ECPA has the advantages of a low sidelobe level better than −20 dB as well as grating lobe suppression.

A wideband high-efficiency dual-polarized metal-only reflectarray antenna is designed and analyzed. The unit cell is composed of a layer of grooved metal plate and a ground, with an air layer in the middle. The proposed element features a phase range of about 360° and works independently in orthogonal directions, enabling dual linearly polarized operations. Based on this unit cell, a circular array including 177 elements with a diameter of 250 mm is simulated and fabricated at 10 GHz. The measured results show that the reflectarray exhibits a good performance in both horizontal and vertical polarizations, with a 1-dB gain bandwidth of 20.2% and 20% and peak aperture efficiency of 62.3% and 61%, respectively. In addition, sidelobe and cross-polarization levels are also satisfactory.

This work provides a comprehensive review of conjugately characteristic impedance transmission lines (CCITLs) and their applications in quarter-wave–like transformers (QWLTs). These promising concepts are employed in the development of miniaturized CCITL-based power dividers (CCITL-PDs). A thorough design procedure for CCITL-PDs with arbitrary power division ratios is presented, including detailed derivations and analysis of the perfect isolation condition. For illustration, an equal-split CCITL-PD implemented using multisection transmission lines (MSTLs) is designed to achieve a 25% reduction in electrical length compared to conventional equal-split Wilkinson power dividers. Although the achieved reduction is modest, this example provides valuable insights and approaches for further optimizations in CCITL-PD design, showcasing its potential for microwave component miniaturization.

A compact low-profile dual-band dual-polarized wearable patch antenna, capable of working in 2.4 and 5.8 GHz ISM band for either on-body or off-body applications with different radiation patterns in each working band, is presented in this paper. The fabricated antenna consists of four layers including modified ground and patch layers and two dielectric layers made of jean fabric, and it has a radius of 30 mm with overall height of 3.4 mm fed by a single probe. The proposed structure is designed in a way that is capable of radiating linearly polarized (LP) waves in lower working frequency and circularly polarized (CP) waves in its upper working band. The ground plane is modified to ensure the dual-band radiation as well as miniaturization of the antenna. The patch of the antenna benefits from truncated corners and four circular stubs which are practically coupled with antenna’s modified ground to provide desired axial ratio and dual polarization capability. With the help of computer-based simulations, the antenna is placed on human body tissue and the calculated amount of SAR values in each band for 1 g tissue is 0.15 and 0.89 Wkg, respectively, which guarantee the safety of the human body in close proximity to the antenna.

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.