In many wireless power transfer (WPT) scenarios, to prevent lateral misalignment between the transmitter (Tx) and the receiver (Rx) and to implement a stable power transfer, multiple Txs are used in place of a single Tx. The existing multi-Tx structures lack flexibility in assembly due to wired connections between Tx units, and face the challenge of variation in power delivered to the load (PDL) in the over-coupling region. A self-organized parity-time (PT) symmetric WPT system comprising dual independent Tx units is proposed in this paper. It provides two operating modes by activating one or two Tx units, offering not only a stable but also an identical PDL. This is achieved by strategically using a scaled PT-symmetric structure when activating only one Tx unit with a scaling factor of 2, and synchronizing the oscillation when activating dual Tx units with the help of existing mutual coupling between them. The theoretical analysis is validated by simulations and experiments. The proposed structure addresses the performance valley region that exists between two side-by-side traditional single-source single-coil structures. Moreover, compared to traditional single-source dual-coil structures, it extends the lateral transfer range rate from 20% to 100% and offers flexibility in assembly.

This paper presents a broadband rectifier based on GaN high electron mobility transistor (HEMT). The continuous class-B/J rectifier operation mode is analyzed in detail. The relationship between the continuous mode class-B/J rectification efficiency and the output capacitance Cout and the on-state resistance Ron is built and the rectification model is firstly presented. Then, the available impedance design space can be determined based on the rectification efficiency model. Considering the package parameters of the CGH40010F, design space at the package plane has been presented. Moreover, a broadband phase tuning network (PTN) is adjusted to satisfy this impedance space. Thus, a broadband transistor-based rectifier can be designed using the continuous class-B/J mode and the PTN. For validation, a rectifier working in 2.4–3.3 GHz was fabricated using CGH40010F. The rectification efficiency varies from 66% to 78% when RF input power is 10 W. Compared with other transistor-based rectifiers, the presented rectifier has a competitive working bandwidth.

This paper introduces a high-power, compact active integrated antenna with extended voltage tuning capability, featuring a nearly 1 GHz oscillation range in the X-band (8.35–9.21 GHz). This broad frequency range enhances the oscillator’s flexibility and adaptability for advanced applications in radar systems and wireless communication. The design integrates InGaAs HEMT technology using a feedback circuit. The self-oscillating antenna, manufactured on a RO4003C substrate with a height of 0.508 mm and dimensions of 0.23 × 0.27 ${{\lambda}}_0^2$, demonstrates impressive performance through small- and large-signal analyses. The obtained results are based on harmonic balance simulation using the auxiliary generator technique within the Advanced Design Systems (ADS) tool. Simulation results indicate power levels from 10.928 dBm to 8.062 dBm, while measured output power ranges from 10.90 dBm to 7.916 dBm, and Equivalent Isotropically Radiated Power (EIRP) values were between 12.68 dBm and 10.198 dBm in the interval 8.35–9.21 GHz. Phase noise measurements are −102.94 dBc/Hz at 1 MHz and −124.13 dBc/Hz at 10 MHz. The simulated and measured results are in good agreement, highlighting the robustness and reliability of the oscillator, as well as the effectiveness of the design, which is well suited for applications requiring high stability, precise frequency control, high output power, and efficient performance for microwave applications.

This work proposes an integrated pulse transmitter with polarization reconfigurability. A reconfigurable pulse-triggered network is designed and seamlessly integrated with a dual-polarized radiator within the compact transmitter structure. This integration allows the radiator to sequentially perform DC charge accumulation, pulse oscillation, and radiation during each pulse cycle. Moreover, the reconfigurable pulse-triggered network introduces two operating modes, enabling the pulse transmitter to switch between different polarization states. Experiments demonstrate that the proposed pulse transmitter can directly convert DC energy into radiated pulses with switchable polarization modes. The pulse signal with a peak-to-peak voltage of 1.6 V is received in the −45° polarization direction at 1.5 m under mode 1, and switches to +45° polarization with a peak-to-peak voltage of 1.6 V under mode 2.

This paper presents a novel compact substrate-integrated waveguide (SIW) antenna that can be utilized for several applications, such as fifth generation (5 G), internet of things (IoT), artificial intelligence, and medical applications. Six antennas are designed. In addition, there are single SIW, 2 × 1 arrays, and 4 × 1 arrays with and without slots. The proposed feeding method is implemented to create a slot antenna array with incorporating KS connector. The proposed designs target the 25–28 GHz band, covering up to 3 GHz of bandwidth depending on the configuration. The structures are designed and simulated using a numerical technique package (CST). The simulation results demonstrate that the SIW antenna array functions efficiently in terms of the gain, return loss, and radiation patterns. Furthermore, the proposed structures have a total volume of 62 mm × 55 mm × 0.508 mm. In conclusion, the experimental results demonstrate that the performance of the proposed antenna is in good agreement with the simulations. Moreover, the gain increased from 8.5 dBi for the single SIW antenna to 14.7 dBi for the four-element array at 26 GHz, indicating a 72.9% improvement.

Presented in this study is a compact, dual-band, and highly flexible inverted slotted triangular-shaped monopole antenna. It is backed with a dual-band artificial magnetic conductor for off-body wireless and low specific absorption rate (SAR) medical applications. The antenna is designed to radiate at 2.45 GHz of the Industrial, Scientific, and Medical-band and achieves dual-band resonance by etching two inverted L-shaped slots off the monopole antenna. By doing so, the antenna operates at 5.2 GHz of the wireless local area network frequency band. In off-body operation, the integrated design achieves gain improvements at both operating frequencies by 6 and 4.9 dBi, respectively, compared to the standalone antenna. In the case of the on-human-body operation scenario, low SAR levels of 0.39 and 0.07 W/kg were realized at both resonant frequencies, respectively. The proposed integrated design was fabricated and tested, where the tested results highly align with the simulated ones in free space and on-body cases. The antenna size is only 39 × 25 mm2 which is claimed to be an ultra-size. Thus, the presented antenna is claimed to be very competitive in terms of the small size and the achieved antenna parameter results.

A compact low-SAR antenna for the Wireless Body Area Network is tailored using Characteristic Mode Analysis exciting the dominant modes. The novel antenna structure produces resonance at 2.45 and 5.9 GHz. The antenna with the dimensions of 0.286λ₀ × 0.265λ₀ × 0.012λ₀, for free-space wavelength. To make the antenna compatible with the human body, an Artificial Magnetic Conductor is incorporated. This engineered periodic structure achieves 0° reflection phase at 2.45 and 5.9 GHz, effectively mimicking a perfect magnetic conductor at these frequencies. The AMC-coupled antenna had resilience to body effects providing isolation. This also makes the antenna human compatible by reducing the Specific Absorption Rate of the antenna below 1.6 W/kg and enhancing the gain of the antenna. The fabricated prototype is experimentally validated using minced meat as a biological phantom. This confirms the feasibility of magnetically engineered reflective surfaces for antenna making it suitable for human wearable applications.

Radio frequency (RF) coaxial connectors are crucial in high-speed digital systems for data transmission. Connectors applied in harsh environments will be degraded over time, affecting the signal integrity. At present, a suitable equalization technology is of substantial value for enhancing the quality of high-speed signal transmission. However, there is limited research focusing on specific equalization designs for degraded connectors. In this current work, based on the theoretical analysis, simulations validation and experimental testing, an equivalent circuit model of the degraded connector was developed. Furthermore, an equalization structure consisting of series resistance and capacitance was proposed. The transmission loss caused by the connector degradation was compensated effectively using this method. Meanwhile, eye diagram characteristics were improved significantly at the receiver where zero timing jitter and an almost full eye opening were achieved. Equalization enhances the eye opening factor by over 50% compared to the uncompensated system. This paper integrates electrical contact theory with high-speed equalization design. Tools and guidance were provided through the proposed modeling techniques for studying equalization effects of this degraded connector system in designs and applications.

A ϕ2.5 m Gregorian antenna has been designed, analyzed, developed, and tested for a contoured beam for India and its Islands. The downlink band is 11.7–12.2 GHz. Uplink band is 17.3–17.8 GHz. The frequency band ratio is 1:1.52. The feed system consists of a radial corrugated horn and a turnstile orthomode transducer. Since there is a common feed system for Ku-Tx and Ku-Rx bands, it causes a large variation in the phase center for Tx and Rx bands. This large disparity in Tx and Rx phase center makes shaping challenging to achieve higher edge of coverage (EoC) gain, over widely separated transmit and receive bands. The optimization is carried out to achieve enhanced EoC gain and compliance of cross-polar isolation (XPI) through surface shaping of main and sub-reflectors. We have also optimized the feed coordinate to achieve the goal. The scattered near field at feed aperture is also minimized to get good XPI. Minimum radius of curvature of the surfaces has been controlled, which is required for the manufacturing of sub- and main-reflectors with minimum fabrication error. A new technique has been devised for the accommodation of a Gregorian antenna on a spacecraft with suitable radio frequency (RF) clearance. The impact of photogrammetry targets on RF performance is also brought out in the article.

This study presents the design and analysis of a dual linear polarized sinuous antenna (DLPSA) optimized for ultra-wideband applications, such as remote sensing of longitudinal metallic targets and microwave imaging systems. The capability of the sinuous antenna to generate dual linearly polarized radiation patterns makes it a strong candidate for these applications. A key design challenge lies in developing a practical feeding network that requires modifications to the antenna feed region. The proposed DLPSA antenna achieves unidirectional radiation patterns in the 2–5 GHz frequency band. A prototype was fabricated, with measured results closely aligned with the simulations. The antenna demonstrates enhanced return loss, gain, and radiation pattern performance compared to existing designs. Additionally, the dual linear polarization capability was verified through co- and cross-polarization measurements conducted in an anechoic chamber.

In this article, a 1 × 2 bandwidth (BW) and frequency-reconfigurable dielectric resonator-based multiple input multiple output (MIMO) antenna array is presented for 5G sub-6 GHz (3.3–6.0 GHz)/Wi-Fi 6E (5.925–6.425 GHz)/Wi-Fi 5G (5.15–5.85 GHz) applications. Additional dual-ring-open loop resonator structures with varied dimensions are introduced within antenna’s feeding network to achieve BW and frequency reconfigurability. RF PIN and varactor diodes (VDs) are integrated with proposed structure to enable switching between various modes and continuous tuning of frequency and BW, respectively. Further, Taguchi neural network (TNN) has been incorporated to predict percentage bandwidth of proposed antenna, getting a maximum deviation of only 0.6% from actual value. The proposed structure operated from 4.98 to 6.5 GHz, achieving wide continuous frequency tuning of 20.36% in passband and 6.1% reconfiguration for notch band. It also demonstrates continuous BW tunability from 16.69% to 34.44% with measured BWs of 19.58%, 34.44%, and 16.69% at 0, 3, and 8 V reverse bias voltages of VDs, respectively. MIMO antenna array structure also shows enhanced gain performance with a peak gain of 11.03 dBi and an overall gain above 7 dBi in the whole operating band.

This paper proposes a broadband, low-profile, dual-circularly polarized (CP) active phased array modular subarray. The subarray elements adopt dual-CP stacked microstrip patch antennas to expand the bandwidth. Each subarray has a complete structure and function, which can be used independently or extended to meet the requirements of different application scenarios. The impact of asymmetric plane is counteracted by a mirror-feed technique, which improves the consistency of scanning gain and axial ratio (AR) at both positive and negative angles. Meanwhile, the subarray can simultaneously form two beams of left-handed circular polarization (LHCP) and right-handed circular polarization (RHCP) for scanning. Finally, a modular subarray prototype with an 8 × 8 array scale was simulated, fabricated, and measured. The simulation results show that the scanning gain decreases by less than 2.19 dB at ±45° and 5.4 dB at ±60° at the frequency of 12.1 GHz. Moreover, within the frequency range of 10.23–12.77 GHz (22.08%), the active voltage standing wave ratios (VSWR) of LHCP and RHCP in the azimuth and elevation dimensions of the subarray are below 2, and the AR in the beam scanning range of ±45° and ±60° are less than 3 and 6 dB, respectively.

In this paper, a dual-band dual-circularly polarized (CP) patch antenna with integrated coupling structure and stepped impedance resonators (SIRs) is proposed. The tapped-line coupling generates $0^{\circ}/180^{\circ}$ phase in two frequency bands, while the parallel coupled-line coupling exhibits an inherent $90^{\circ}$ phase delay in two frequency bands. The two-way coupling structure generates the $\pm90^\circ$ phase shift enabling dual-CP, eliminate the need for additional phase shifters. Then, the SIRs excite the two orthogonal modes of the radiation patch while concurrently matching the impedance between the antenna and the input port, eliminating the need for an additional matching network. Finally, the radiation patch and SIRs are integrated into a complete structure, and a T- junction is used to connect the two branches. Compared to traditional design, the proposed antenna greatly reduces the complexity and difficulty. The development stages are discussed in detail. The proposed design is demonstrated through prototype fabrication and characterization.

This work proposes a small, wideband circularly polarized planar monopole antenna. The antenna comprises a modified C-shaped radiating patch and a truncated rectangular ground plane with a small open-ended slot to achieve a wideband circular polarization property. The proposed antenna has a compact volume of 0.57 λ0 × 0.45λ0 × 0.024λ0 (where λ0 is the free space wavelength at resonant frequency of 4.5 GHz). It provides a measured fractional impedance bandwidth of 50.70% and fractional 3 dB axial ratio bandwidth of 45.04%. The measured peak gain of the antenna is 7.4 dBi. It also maintains a gain of more than 6 dBi throughout the entire band. The mechanism of circular polarization is also described herein. A parametric investigation of various design parameters has also been prepared herein. The proposed model was simulated using the High Frequency Structure Simulator, and measurements were conducted to validate the simulated results. The simulated and measured results of the various characteristics of the proposed antenna are presented. Owing to its low-profile, wideband, and circular polarization characteristics, the proposed antenna is applicable for different wireless applications.

A metasurface (MTS) antenna with wideband radiation and low radar cross section (RCS) performance is proposed. The design is based on a two-step RCS reduction (RCSR) strategy applied to a reference antenna – a conventional 4 × 4 square patch array MTS antenna that exhibits stable broadside radiation within 5–6.5 GHz. In the first step, the patch array of the reference antenna is reconfigured into a quasi-chessboard MTS using the principle of reflection cancellation, enabling wideband RCSR under both x- and y-polarized incidences. In the second step, guided by the antenna scattering theory based on characteristic modes, six slots are etched on the ground plane to further enhance RCSR under x-polarized incidence. Characteristic mode analysis is employed throughout the design process to simultaneously analyze radiation and scattering behaviors. Compared with the reference antenna, the proposed MTS antenna maintains similar radiation performance while achieving monostatic RCSR bandwidths of 3.7–11.3 and 4.7–11.3 GHz for x- and y-polarized incident waves, respectively. It also demonstrates significantly broader RCSR bandwidths compared to a metallic plate of the same size.

Body-centric and body-worn applications have gained much more attention due to the emergence of wearable electronics. Antenna designs suitable for body-centric communications have then become a crucial part of any wearable system. This article introduces an ultra-wideband (UWB) antenna with dimensions of 24 × 18 × 0.8 mm3, designed using a flexible jean substrate. Using a slotted patch and defected ground, a wide impedance bandwidth of 15 GHz was achieved. A novel multiple input multiple output (MIMO) configuration with extended swastika-shaped connected ground is proposed to improve the reliability in body-centric communication. Frequency selective surface (FSS) is deployed to reduce specific absorption rate (SAR) and also to achieve directional radiation pattern at a specified frequency range to support both on- and off-body communications. A novel approach of corner-connected inter-rotated square rings was used to achieve wideband response. With the proposed FSS, the antenna renders a good peak gain of 9.1 dB, with the efficiency ranging from 72% to 94% in the UWB spectrum. The FSS proposal also helped in bringing down the SAR within the limits. All the MIMO diversity parameters reported remain good enough, ensuring link reliability. Real-time on-body measurements were carried out at various body parts. The path loss obtained while using the proposed antenna is considerably minimal. Satisfactory results were obtained from the time domain analysis carried out, which ensures good pulse similarity and minimum phase variations.