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.

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.

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.

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.

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.

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.

Diabetes is increasingly recognized as a serious, worldwide public health concern. In this paper, an extreme learning machine (ELM) based on time-domain pulses was introduced to obtain noninvasive glucose detection. To validate the method, time-domain signals from different concentrations of glucose solutions were detected in the model. Considering that the glucose levels of diabetic patients range from 30 to 500 mg/dL, the glucose solution concentration was set to 10−500 mg/dL, with an interval of 10 mg/dL. The received signals were trained using the ELM algorithm, which was able to accurately predict solutions of unknown concentration with an average relative error of 1.45%. The proposed method is rapid to process, simple to operate, and highly accurate for noninvasive glucose detection. The results demonstrated that microwave detection technology combined with the ELM algorithm has the potential to become a valuable tool for noninvasive glucose monitoring in clinical settings.

This paper presents a novel UHF RFID tag antenna with metal-mount capability, broadband characteristics, and frequency controllability. To achieve anti-metal performance, we explore a vertical loop structure as the main radiator, with slots for frequency adjustment and layout flexibility. The antenna operates based on a hybrid magnetic–electric mode interaction mechanism, in which the vertical loop provides a magnetic-dipole-dominated radiation mode. Furthermore, asymmetric resonant dipole patches are loaded on both sides of the center feed line to introduce an auxiliary electric mode and broaden the operating bandwidth. This structural-level mode and coupling engineering enables independent control of the center frequency while maintaining wideband impedance matching. The proposed antenna has a compact size of $0.1951\lambda \times0.128\lambda \times0.0051 \lambda$, with the main radiation lobe concentrated within 60$^{\circ}$ from the zenith. By mounting on a $100\times100\times2\,\mathrm{mm}^{3}$ copper plate, it achieves a maximum read range of 7.32 m, which demonstrates the good adaptability for UHF RFID tagging on metal surfaces.

This research paper proposes an innovative, mathematically engaging, and compact Dual Staircase-Shaped Fractal Antenna (DSSFA) using an HSA-ANN Ensembled integrated approach. The revealed structure bearing size 26 × 32 × 1.6 mm3 is tailored on an easily accessible FR4 substrate and backed by a modified ground plane. The considered fractal radiator is designed iteratively and exhibits a symmetrical dual staircase-shape. During the generation process, the framed HSA-ANN Ensembled integrated strategy offers the targeted frequency points. The developed heterogeneous ANN Ensembled Models are employed for the prediction of two critical design parameters (feed position and ground length). Afterward, the trained Ensembled models are utilized in the fitness function of the HSA for the creation of optimized operating points. Furthermore, laboratory measurements on the Realized DSSFA are carried out to justify the feasibility of the described fractal approach. The examined resonant points are 2.48, 3.58, 4.25, 7.65, 8.74, 11.83, and 14.44 GHz. At the claimed resonant points, the said antenna is characterized by stable partially deformed omnidirectional/bidirectional radiation patterns. The demonstrated fractalization technique allows the physical size to be reduced by 33%. Based on the experimentation, it has been stated that the introduced antenna is intended for use in distinct wireless applications.

This paper presents a novel planar balanced-to-balanced diplexer with high isolation and harmonic suppression. Both the lower and higher channels of the diplexer consist of the two-stepped impedance resonators and one uniform impedance resonator. To enhance the inter-channel isolation of the diplexer, the cross-coupling between the resonators is used to introduce extra out-of-band transmission zeros. By utilizing stepped impedance resonators with different impedance ratios, the harmonics of the three resonators, except the fundamental harmonics, are different from each other so as to suppress the odd- and even-mode harmonics effectively and ultimately to achieve the purpose of broadening the stopband and enhancing the common-mode (CM) suppression. To verify the feasibility of this design, a microstrip prototype with dual-channel center frequencies of 2.01 GHz and 3.54 GHz was manufactured. Experimental results demonstrate that the in-band differential-mode (DM) isolation is higher than 41.6 dB and 41.5 dB for the lower and higher channels, respectively. CM suppression is greater than 20 dB in the 0–13.7 GHz range for the lower channel and 20 dB in the 0–9.0 GHz range for the higher channel. The stopband suppression level achieves 20 dB up to 18.5 GHz.

This paper presents a broadband metasurface (MS) antenna designed through characteristic modes analysis. By introducing horizontal slots into a 3 × 3 MS array, a pair of degenerate modes is successfully separated and the dominant mode is reconfigured as TM10 mode. Optimizing feed position simultaneously excites the TM10 modes of both the patch antenna and the MS, expanding the −10 dB impedance bandwidth from 4.09–4.22 GHz to 3.45–4.5 GHz with a gain variation of less than 1.9 dB. Furthermore, a dual-port multiple-input multiple-output (MIMO) antenna is constructed by orthogonally arranging two elements. The exclusive TM10 mode enables inherent decoupling, achieving over 23.6 dB isolation. Measured results exhibit good agreement with simulations, demonstrating an operational band of 3.44–4.39 GHz, effectively covering the 5G NR (New Radio) n48 band.

This paper presents a quad-port triplexer structure designed for next-generation wireless portable devices. The proposed triplexer consists of three bandpass filters isolated from one another. Filters 1 and 2 are designed using identical coupled line structures with varying physical properties, while filter 3 is developed with a novel coupled line structure. The modified coupled line enables a compact triplexer design, enhances isolation and bandwidth, and reduces the insertion loss. A comprehensive analysis of the proposed triplexer is conducted, and the S-parameter response demonstrates that the triplexer operates at 2.91, 4.43, and 1.20 GHz, with fractional bandwidths of 30.2$\%$, 22$\%$, and 33.3$\%$, respectively. The in-band return loss is better than 12.3 dB across the entire passband. Additionally, the triplexer features three transmission poles for the first two passbands and two for the third. The in-band insertion loss is less than 0.63 dB for all three passbands. The measured performance of the fabricated triplexer closely corresponds to the simulated results, validating its effectiveness in achieving the desired specifications. This makes the triplexer highly suitable for 5G networks and IoT-based wireless communication devices that demand multiband, high-performance filtering.

This paper presents a compact dual-band multiple-input multiple-output (MIMO) fractal antenna based on a novel butterfly-flock iterative ring structure. Each MIMO element is formed through three fractal iterations, where every added ring is half the size of the previous one and rotated by 90° in anti-phase, creating extended current paths and inherent spatial polarization diversity. The antenna achieves wide operating bands of 1.1–5.6 GHz and 7.4–9.7 GHz, covering GPS, 3G, WLAN, LTE, WiMAX, 5G, and satellite communication systems. Compared with earlier designs, the proposed structure demonstrates improved diversity performance, including a low Total Active Reflection Coefficient and a low Channel Capacity Loss. With a compact size of 30 × 40 × 0.8 mm3, the design is suitable for integration into modern portable wireless devices.

Inductive wireless power transfer (WPT) systems require compensating capacitors to operate efficiently. However, these capacitors can introduce additional costs, weight, and losses, particularly at MHz-range operating frequencies. To mitigate these issues, self-resonant coils can be used by exploiting the parasitic capacitances inherent in double-layer printed circuit boards (PCBs). In this work, a double-layer coil for a self-resonant series WPT system is developed for operation at the AirFuel standard frequency of 6.78 MHz. Unlike conventional design methods adopted for self-resonant coils, mainly based on analytical formulations, the proposed approach employs Finite Element Method simulations that couple electro-quasistatic and magneto-quasistatic formulations. This approach enables accurate evaluation of the self-resonant frequency (SRF) as well as the current distribution along the PCB layers, revealing significant non-uniformity. Building on this insight, copper trace length is reduced to save material while maintaining performance in terms of operating frequency. Both the full-trace and reduced-trace coils are fabricated and tested, showing good agreement with simulations. Notably, the proposed reduction in the copper trace affects the SRF by only 3% compared with the full-trace design.

Based on practical requirements, this paper presents the design, fabrication, and experimental validation of a Ka-band wideband two-dimensional (2D) phased array antenna with 45° slant polarization. The array integrates a polarizer with 28 six-element metallic Vivaldi linear sub-arrays. To the best of the authors’ knowledge, no previous work has reported the engineering implementation of a polarizer-integrated 2D phased array at Ka-band, as existing studies are limited to single elements or one-dimensional arrays. Measured results show that the array achieves an active Voltage Standing Wave Ratio (VSWR) below 2.6 over 32–40 GHz, with a gain exceeding 25.5 dBi. It supports wide-angle scanning up to ±50° in the azimuth plane and ±30° in the elevation plane, with a scan loss not exceeding 3 dB across the entire scanning range. Furthermore, the amplitude difference between horizontal and vertical polarization components remains within 2.9 dB throughout the scanning range, confirming desirable slant polarization characteristics.

In this paper, a dual-frequency switchable wireless power transfer (WPT) system based on parity–time (PT) symmetry is proposed. For the transmitter, a high-efficiency switch-mode amplifier is employed as the negative impedance to provide the required gain. To realize dual-frequency operation, the magnetic coupling coil is designed as triple-tap structure which can be used to create two distinct series inductor-capacitor (LC) resonant branches by switch. At the receiver, two parallel inductor-capacitor-resistor (LCR) resonant circuits with corresponding dual operational frequency of transmitter are adopted to achieve stable energy reception. The transmission characteristics of the system under different frequency switching modes are analyzed theoretically and verified experimentally. The results demonstrate that, whether operating in the low- or high-frequency mode, the system can maintain the PT-symmetric state in the strong coupling regime, achieving robust and efficient WPT with system efficiency >80%. The proposed dual-frequency switchable WPT system can offer a theoretical reference for practical reconfigurable wireless charging applications requiring dual operating frequencies.

We present a general analysis of a densely interleaved array (DIA) transmitter, which can transmit two independent beams with the same polarization at closely spaced frequencies from the same aperture. We use standard array theory to show that the array factor and bandwidth of the DIA remain comparable to those of a uniform linear array (ULA). The analysis also reveals that the effective isotropic radiated power (EIRP) of the DIA is 3 dB lower than that of a ULA; however, the two beams can be combined into one, which results in an EIRP increase of 3 dB over the same ULA. We validate the theory by building a DIA demonstrator consisting of two 8-element ULAs of reflector-backed dipoles, which have been interleaved with one another with quarter-wavelength spacing, having the same polarization, and two dummy elements on either end. Half of the dipoles operate at 2.39 GHz and the other half at 2.41 GHz. Even with increased mutual coupling between the antenna elements, the active interaction between the two tones does not generate significant mixing products. The DIA offers good versatility and allows for free-space power combining, which can effectively reduce the output power requirements of the transmitting (TX) amplifiers.

This paper presents a novel self-octuplexing substrate-integrated waveguide (SIW) cavity-backed slot antenna for eight-band wireless communication services. This antenna employs eight semi-elliptical-shaped slots on an octagonal SIW cavity with different lengths to radiate at eight different frequencies. The eight radiating frequencies are 2.7, 3, 3.3, 3.6, 3.9, 4.2, 4.5, and 4.72 GHz, with impedance matching is less than −10 dB. Each radiator is backed by an eighth-mode SIW cavity and excited by a 50 Ω microstrip line. A designed prototype of the antenna is fabricated and tested. It has more than 34 dB measured isolation among any two ports. The maximum measured antenna gains are 4.4, 4.19, 4.11, 4.03, 4.19, 4.28, 5.2, and 5.44 dBi at the respective operating frequencies. It has a measured cross-polarization level of below −24.2 dB in the boresight direction and a front-to-back ratio of more than 10.4 dB in all the bands. All the slots can be tuned independently to radiate at the desired frequency band. This antenna can easily be integrated with other planar circuits due to an unperturbed ground plane.