In this work, a novel hybrid algorithm is introduced that combines the range migration algorithm (RMA) and the back projection algorithm (BPA). The traditional image reconstruction algorithms used for synthetic aperture radar each have trade-offs between computational efficiency and imaging accuracy. The proposed hybrid RMA–BPA approach leverages the computational efficiency of RMA for the initial image reconstruction and object detection, followed by BPA for the refined, high resolution of the cropped region of data. The method of focusing computational resources on the smaller cropped datasets that contain the objects significantly reduces the processing time compared to that of traditional standalone BPA. The hybrid approach’s performance was evaluated over three different scenarios, providing a reduction in computation time for each scenario. Due to the algorithm’s approach to crop the dataset for the specific object, the increased efficiency varied. The different scenarios each produced different times to compute; however, the most impressive result delivered a 75.2% reduction in computation time compared to traditional BPA, without sacrificing the accuracy of the image. The hybrid approach is especially suited for applications that require precise object detection in healthcare, oil and gas, security, and industrial inspections.

In this work, a flexible antenna as an Radio Frequency (RF) sensor is presented, which is used in Wireless Body Area Network communications. For on-body and off-body communications, the antenna elements have directional and quasi-omnidirectional patterns. This antenna is transparent, made from a polydimethylsiloxane (PDMS) substrate, which is well-known for its flexibility, with copper as its conducting element. The proposed design uses a PDMS substrate with a loss tangent tan δ of 0.02 and a dielectric constant εr of 2.65. The overall size of a compact antenna is 36.98 × 29.8 × 1 mm, which provides a wide impedance bandwidth that covers the wideband spectrum. Using slots and stubs, antennas were modified as a simple geometrical configuration to achieve a flexible and compact antenna size. The presented design is simulated by CST Microwave Studio with a range of operating frequencies from 3.26 to 4.62 GHz, a bandwidth of 1.36 GHz, and a gain of 2.42 dBi in its planar form. This achieves the required compactness, backward radiation, minimization loss, and targeted frequency bands for frequency notch characteristics used in the human body of proximity.

This work proposes a novel crossover cavity with high isolation and power handling capability. It consists of a one-pole Substrate Integrated Waveguide (SIW) circular resonator that excites two decoupled evanescent modes at the same resonant frequency. The proposed structure deploys two substrates acting as one evanescent-mode circular cavity. The electric fields of the evanescent modes are confined in the secondary substrate. Meanwhile, most of their magnetic fields exist in the main substrate. Each semicircular post is loaded by a capacitive load ($C_{1}$) in the secondary substrate, defining the resonant frequencies of the excited modes. Moreover, the isolation between channels is controlled through capacitive slots in the top metal layer of the main substrate. Consequently, the resonant frequency of the proposed crossover cavity and the isolation between its channels are independently tuned. The proposed SIW crossover cavity is implemented at 8.7 GHz with a size of (0.65$\lambda_{g}\times $0.65$\lambda_{g}$). A high-power handling capability of 44.7 dBm is measured. Also, 1.7 dB and 64 dB levels of insertion loss and isolation are measured, respectively. Furthermore, a 50-dB isolation bandwidth of 739 MHz is achieved. The scalability of the one-pole crossover cavity to a second-order transfer function has been demonstrated in a simulated two-channel crossover configuration.

Class-D amplifiers offer significant potential for achieving efficient and high-power RF amplification. By converting the collector dissipation of conventional amplifiers into load power components and employing filtering to eliminate unwanted frequencies, Class-D amplifiers achieve superior overall efficiency. This study proposes and investigates a high-efficiency push-pull Class-D power amplifier integrated with a carefully designed matching network. To validate the proposed amplifier’s performance and practical applicability, a proof-of-concept circuit was designed and fabricated. Operating within a frequency range of 7.7 –8.7 MHz, the amplifier achieved notable results, including a power-added efficiency of 89.26% and an output power of 49.54 dBm. The consistency between simulated and measured results underscores the reliability of the proposed design and its potential for practical deployment. This work demonstrates the suitability of the amplifier for wireless Radio Frequency Identification applications, offering a highly efficient solution with enhanced output power and performance. To the best of the authors’ knowledge, this study provides a novel approach to achieving exceptional efficiency and output power, representing a significant advancement in the field of RF power amplifier design.

This paper presents a low-cost, high-gain 1 × 4 collinear slot phased array for 5G millimeter-wave (mmWave) applications, which is realized on a two-layer standard printed circuit board. The design specifically addresses two key challenges in mmWave phased array design, which are mitigating the strong mutual coupling that limits wide-angle scanning performance and enabling the low cross-polarization radiation structure. A key innovation is the use of a periodically bent ridge within a ridge substrate integrated waveguide to efficiently excite a centerline collinear slot configuration, which minimizes cross-polarization. Furthermore, a compact via-based choke structure is introduced to suppress mutual coupling and thus achieve high inter-element isolation. The fabricated prototype exhibits an impedance bandwidth of 10.7% (26.5–29.5 GHz). The measured results show a peak gain of 14.5 dBi, port isolation better than 19 dB, and a stable 3-dB scanning range of ±50°. These results validate the proposed design as a compelling low-cost solution that achieves an excellent balance of high gain, wide-angle scanning, and high isolation.

A compact antenna aperture tuner for an inverted-F antenna is presented using a high-voltage enhancement-mode p-GaN gate high electron mobility transistor (HEMT) RF switch with a gate length of 0.5 µm. The proposed design achieves a breakdown voltage of 100 V for a single p-GaN HEMT switch, enabling the replacement of conventional stacked high-voltage RF metal-oxide-semiconductor field effect transistor (MOSFET) configurations. A 4-bit switched-capacitor network based on p-GaN HEMT devices is employed to cover the n77 (3.3–3.8 GHz) cellular frequency band. Measured results show that a return loss exceeding 6 dB is obtained at the antenna feed point over more than 90% of the target frequency range. Under a continuous wave of 34 dBm, the measured reflected second- and third-order harmonics (H2 and H3) are −56 and −75 dBm, respectively. These results demonstrate the feasibility of p-GaN HEMT-based RF switches for compact and high-voltage antenna tuning applications.

The proposed research aims to develop an efficient sidelobe canceller beamforming antenna array for scanning and anti-jamming purposes in radars with time-modulation. Time-modulated antennas are unconventional alternatives to phased arrays, in which the phase deviations between the impinging signals can be controlled by suitably switching ON and OFF the array elements at different time instants. This research addresses the design of a quantum-inspired optimal time-modulated beamformer, aiming for a broad scan coverage of 90° towards broadside. The scanned beams are generated using quantum algorithm-inspired time schemes, in which the ON times of each element are optimized to achieve the optimal radiation characteristics. The beamformer simultaneously aimed to suppress the sidelobes of the scanned radiation patterns. The proposed beamformer is designed for an 8-element antenna array, and the incorporation of time-modulation and its inherent harmonics generation enables simultaneous beam scanning over a desired region. The scanned patterns with reduced sidelobes are further exploited for the strategic null placement by proposing the time-modulated single-point anti-jammers. The concept is further extended, and an 8-element beamformer is developed for sectorized anti-jamming to show the efficiency, effectiveness, and robustness of the proposed research. Multiple sectors in the angular region are targeted by exploiting the harmonics and suppressing them below a desired level. The sidelobe canceller beamformer also demonstrates decent performance, suppressing sidelobes below 20 dB across all applications. The radiation power efficiency of the beamformer is more than 78%. The proposed sidelobe canceller time-modulated beamformer is also compared with other related research for a detailed comparison.

A microstrip low-pass filter with sharp roll-off and excellent suppression in both the near- and far-stopbands is proposed. The design incorporates a stepped-impedance hairpin-type resonator (SIHTR) along with a pair of asymmetric T-shaped resonators (TSRs). While the SIHTR offers a tunable 3 dB cutoff frequency and roll-off rate (ROR), its near-stopband suppression degrades at higher ROR values. To address this limitation and further extend the stopband bandwidth, two TSRs with distinct resonant frequencies are positioned at the input and output ports. By fixing their resonant frequencies and fine-tuning their stopband characteristics, the overall suppression bandwidth and stopband attenuation are significantly enhanced. The proposed filter features a compact layout, high selectivity, a wide stopband, and excellent out-of-band suppression performance. Measured results demonstrate an insertion loss of less than 1 dB and a return loss of greater than 15.1 dB in the passband from DC to 7.5 GHz. The 3 dB cutoff frequency is 8.23 GHz, and the transition band is 34.58 dB/GHz from -3dB to -40dB. In the stopband, attenuation exceeds 31.5 dB across the frequency range from 9.17 GHz to 40 GHz.

This article examines the benefits of utilizing site and orbital diversity reception techniques at Ka- and Q-bands in South Eastern Europe, comparing their performance in Cyprus and Greece. The assessment relies on measured rainfall rate statistics, collected near the selected locations in both countries. The study compares and evaluates the performance of double and triple site and orbital diversity scenarios. The simulation outcome reveals that the adoption of double and triple site, or double and triple orbital diversity configurations leads to considerable enhancements in outage performance in both frequency bands. The delivered improvements are markedly significant when specifically 3-site and 3-orbit diversities are applied, especially at Q-band. However, the orbital diversity demonstrates inferior performance compared with site diversity. Notably, for satellite systems demanding extremely high levels of service continuity, the 3-site diversity approach proves highly effective at Ka- and Q-bands, accomplishing this without necessitating overly large fade margins. Comparing Cyprus and Greece, the latter demonstrates lower outage improvements due to the higher measured rainfall rates. Finally, for a dual orbital diversity scenario in Greece, measured experimental results are presented in terms of joint attenuation and compared with the theoretical model, exhibiting noticeable accuracy.

The pronounced phase noise issue in millimeter-wave (mm-wave) complementary metal oxide semiconductor (CMOS) voltage-controlled oscillators (VCOs) has motivated a wider loop bandwidth in integer-N phase-locked loops (PLLs). In this work, we introduce a quadrature-phase spurious-tone-canceling phase detector (QSC-PD) that decouples the inherent trade-off between PLL loop bandwidth and spurious tone suppression. By incorporating an auxiliary sampling phase detection path, the spurious signals produced by the primary path are effectively canceled without extra power overhead or compromising loop stability. Owing to its high gain, the QSC-PD reduces its own jitter contribution within the loop bandwidth. Furthermore, the QSC-PD facilitates both frequency acquisition and VCO lock detection. Implemented in 0.13 μm SiGe bipolar CMOS technology, the mm-wave PLL attains a spurious tone of −84.5 dBc, a phase noise of −112 dBc/Hz at 1 MHz offset, and a minimum integrated jitter of 57.9 fsrms (1 kHz–300 MHz) at 15.6 GHz. The entire circuit consumes 39.6–44.5 mW.

In three-dimensional (3D) through-the-wall radar imaging, unknown wall parameters such as thickness and relative permittivity distort electromagnetic wave propagation, causing image defocusing and target displacement. Autofocusing is therefore essential, but conventional methods are computationally demanding due to two-dimensional (2D) searches over wall parameters and repeated reconstruction of full 3D images. To address this challenge efficiently, a slice-based 3D imaging strategy is adopted. Radar data are acquired along a linear aperture parallel to the wall at multiple heights. For each height, the collected measurements form a B-scan dataset, which is processed independently to reconstruct a 2D image slice. A computationally efficient two-step framework is proposed. First, the wall’s relative permittivity is estimated from the time-domain response of the B-scan at a selected height, and autofocusing is performed by varying only the wall thickness, reducing the conventional 2D search to a one-dimensional problem. Second, focused 2D image slices are reconstructed at all heights. The final 3D image of the concealed targets is obtained by superimposing these slices into a volumetric representation. The experimental results demonstrate that the proposed technique yields well-focused images while significantly reducing the computational cost.

This paper focuses on the design of a novel 4-port antenna suitable for 5G smartphones operating in the 4–6 GHz band. Element-level structural asymmetry is leveraged to optimize the loss and coupling performance of the multi-element antenna. Relative orientation of the parameterized radiating elements is chosen based on extensive analysis of the current distribution and return loss characteristics. Characteristic modes are analyzed to identify the significant contributing modes, and equivalent circuit analysis is carried out to get insights into the radiation characteristics. Measurements closely matched with the results from simulations and modeling. Specific absorption rate analysis revealed that the radiation levels are within the prescribed safety limits while satisfying the other performance requirements. Hence, this antenna is suitable for 5G applications as it ensures user safety and also aligns with regulatory standards.

The design of double-pole double-throw (DPDT) and single-pole double-throw (SPDT) waveguide switches, along with their actuating mechanisms for high-power applications, is presented. The mechanical waveguide switch is based on gap waveguide technology, which uses a controlled air gap to prevent electromagnetic wave leakage. A rotating inner cylinder enables signal transmission and switching, while a fixed outer cube protects the cylinder and secures the input and output ports. Dividing the switch into two parts simplifies manufacturing and assembly. The switch can withstand a peak power of 100 kW. Its electrical performance is analyzed using CST Studio Suite. The proposed switch is fabricated and experimentally validated, showing strong agreement between simulated and measured results. The return loss exceeds 30 dB, indicating very low reflected power, while the insertion loss is below 0.1 dB, demonstrating minimal signal power loss. The isolation is greater than 90 dB, indicating extremely low leakage between ports. The switching operation is controlled by an actuating mechanism designed using COMSOL Multiphysics. The mechanism operates at 28 V and 0.9 A, achieving a switching time of 50 ms. The proposed design provides high-power handling capability, low loss, high isolation, and fast switching performance.

A sparse high-gain multifaceted circularly polarized antenna array based on partially reflecting surfaces (PRSs) is designed. Circular polarization is obtained by implementing the sequential phase rotation method at the source antenna level. Beamforming is implemented using phase compensation combined with amplitude weighting proportional to the radiated intensity of the given facet in the targeted direction, following the maximum ratio transmission concept. The radiation pattern is scanned across the angular region specified by the angular gap between adjacent facets. The obtained beamformed result shows a maximum gain fluctuation smaller than 0.5 dB across the scanned sector, together with a sidelobe suppression of 10.27 dB, and the obtained embedded element pattern exhibits a flat top.

A multi-objective evolutionary algorithm based on decomposition with an improved hybrid particle swarm optimization (MOEA/D-IHPSO) method is proposed, which aims to enhance the efficiency of automated optimization for antenna geometry. The optimization process includes two stages: optimization problem modeling and algorithm application. In the first stage, the topology optimization regions are selected according to the surface current distribution of the antenna, and a differential grid division strategy is employed to characterize the selected regions, ensuring the modeling accuracy of the key topology areas. By combining the encoded topological parameters of the selected regions with the key size parameters, a hybrid solution vector is formed and subsequently used to generate the initial population. In the second stage, the proposed framework uses new crossover and adaptive mutation operators to accelerate the process of reaching the target solution. Furthermore, MOEA/D-IHPSO incorporates a novel transfer learning-based recombination strategy that directly leverages historical optimization data without requiring surrogate model training, thereby intelligently guiding the search direction. To validate the effectiveness of the method, a dual-polarized omnidirectional antenna is optimized. Experimental results show that the optimization efficiency is improved by 31.8% and 26% compared to IBPSO and MOEA/D-GO algorithms, respectively.

In this paper, a passive, chipless ${2 \times 2}$ RFID tag array designed on a thin polyimide substrate is proposed for a wearable application. The radiating element comprises a star-shaped multi-ring structure enclosed in a square folded split ring. Requirement of compactness in wearables gives rise to electromagnetic interference (EMI) due to close coupling between the tag elements, which deteriorates the performance of the RFID system and requires mitigation of the EMI. In the present work, the coupling is analyzed extensively for two separate cases: when all array elements are of the same size and when they are of two different sizes, to investigate both inbound and outbound EMI scenarios. The orientation of each tag element with specific configuration is examined to achieve minimum coupling and to gain a larger read range, an important parameter in the design of passive RFID tags. Furthermore, specific absorption rate analysis confirms the safety and suitability of the design for on-body applications. The prototype model of the proposed configuration is developed, measured, and compared with the simulation results. A good agreement between the simulation and measured results confirms its suitability for compact wearable applications.

With the evolution from 5G to 6G and the popularization of carrier aggregation technology, mobile terminal devices face challenges in miniaturizing multiplexers and handling concurrent signals across a wide-bandgap. This study proposes a numerical de-embedding design method. By precisely calculating and compensating for the parasitic loads, it achieves deterministic synthesis of matching networks. Based on this method, we designed and fabricated a monolithic integrated surface acoustic wave triplexer on a lithium tantalite on insulator (LTOI) substrate for dual-frequency GPS L1/L5 positioning and Bluetooth (BT) communication. To suppress a specific spurious mode on the LTOI substrate and improve the isolation, a notch inductor structure was embedded into the design. The monolithic integrated triplexer measures 2.5 mm × 2.0 mm × 0.6 mm after packaging. The insertion loss is less than 1.6 dB in both the L1 and L5 bands. In the BT band, the average loss within any 18 MHz range of the passband is below 2.5 dB. The return loss for all three channels is better than −10 dB, while the isolation between channels is maintained at ≈40 dB. The successful fabrication of this triplexer not only validates the design method but also demonstrates its potential for application in miniaturized wearable devices.

This study presents the development of a 3D-printed, wideband, dual-polarized magneto-electric dipole antenna. The proposed antenna demonstrates exceptional cross-polarization isolation (XPI) between its two mutually orthogonal RF ports, achieved through innovative feeding probes, specifically an inverted $\Gamma$-shape and a conventional $\Gamma$-shape probe. The analysis reveals that misalignment between probes can impair XPI; this phenomenon is systematically examined through electromagnetic full-wave simulations. A practical remedy is provided using four plastic rods strategically positioned through the probes and posts. Measurements indicate that XPI exceeds 50 dB across the common operating frequency range of 3.05–4.13 GHz (30%). The maximum realized gain is approximately 7.9 dBi, with a nearly flat response and stable radiation patterns across both ports throughout the bandwidth. The proposed antenna offers a cost-effective, 3D-printed design, wideband radiation performance, and exceptional port-to-port isolation, demonstrating significant potential for full-duplex wireless communication and ICAS applications.

In this paper, we present an ultra-fast technique for brain tumor detection in microwave brain imaging systems based on compressive sensing (CS). To achieve this, we designed an elliptical array-based microwave imaging system by simulating sixteen elements of modified bowtie antennas in the CST medium around a multi-layer head phantom. Additionally, we designed an appropriate matching medium to radiate in the desired band from 1 to 4 GHz. The algorithm section of our technique involves pre-processing steps for calibration, a processing step to create a two-dimensional image of the received signals, and a post-processing step for CS. In the processing section, we used a confocal image-reconstructing method based on delay and sum and delay, multiply, and sum beam-forming algorithms. Finally, we applied a new CS technique that includes an L1-norm convex optimization method to reconstruct low-dimension images from the original reconstructed images. We present simulated results to validate the effectiveness of our proposed method for precisely localizing the tumor target in a human full head phantom. The simulated results demonstrate that by using our proposed CS method, the image reconstruction processing time decreased to 63% and the compressed image size reduced to 25% of the original image.