This paper proposes a compact coplanar waveguide-fed slot antenna for ultra-wideband wearable applications, featuring six notch bands. The antenna utilizes a flexible liquid crystal polymer substrate with a thickness of 0.1 mm. The antenna achieves six band-notched characteristics by incorporating a split concentric ring etched on the radiating patch and L-shaped branches loaded on the ground plane. The proposed flexible antenna has dimensions of 30 × 30 mm2(0.65λ0*0.65λ0,λ0 is the free space wavelength at 6.5 GHz.). Measurement results show an impedance bandwidth ranging from 2.37 to 13.7 GHz and a fractional bandwidth of 134%. The notch bands cover 2.9–3.77 GHz for WiMAX applications, 4.14–4.9 GHz for the ARN band, 5.09–5.55 GHz for the WLAN downlink band, 5.86–6.46 GHz for the C-band uplink band, 6.66–7.39 GHz for the C-band/INSAT/super-extended band, and 7.93–8.43 GHz for ITU-8 GHz. The maximum gain in the operating band is 6.5 dBi. The performances of the flexible antenna are analyzed under bending conditions. The ANSYS HFSS electromagnetic simulator was used for the design and simulation of the proposed antenna. The flexible antenna is suitable for wearable applications.

The antenna characterization from planar near-field (NF) measurements is generally realized by using the classical NF to far-field transform technique of plane wave expansion (PWE). This approach imposes strong constraints on NF sampling. To overcome these limitations, an equivalent model of the antenna under test (AUT) is created based on a distribution of infinitesimal dipoles. A reduced-order model (ROM) of the problem is constructed to obtain a decomposition basis defining the radiated field. The powerful ability of the ROM in determining the number of points needed for accurate NF measurements is demonstrated. Also, efficient non-conventional sampling strategies are applied to the case of planar NF measurements and the influence of these distributions on the reduction of the number of samples is studied. The global analysis of our approach on simulated and measured NF data shows that only 20% of the total number of points are needed with respect to the classical PWE technique to achieve an accurate characterization.

Multipath components (MPCs) are both the challenge and the resources to exploit in high-frequency wireless communication, especially in environments with complex reflections. On the one hand, late-arriving MPCs cause inter-symbol interferences in digital communication. On the other hand, techniques such as multiple-input multiple-output and rake receivers have been widely applied to utilize the information carried in the math-path components. To this end, identifying and clustering MPCs is the foundation for tackling the challenges and boosting the utilization of reliable and correct information. Past research focuses either on extracting the path information or on clustering the extracted components. In this paper, we propose a complete workflow that performs identification as well as clustering of MPCs. We extend our previous work in clustering algorithms to indoor propagation measurements of three different frequency bands, as well as multiple transmitter–receiver locations. We verify that the fast attenuation of terahertz-band signals results in clear separations of peaks in measurements, which in turn facilitates the identification and clustering solutions. The ease of application highlights the wide-applying potential of high-frequency communication.

A novel high-selectivity ultra-wideband (UWB) balanced bandpass filter (BPF) with harmonic suppression characteristics is proposed. The differential-mode UWB passband is constructed using quarter-wavelength asymmetrical parallel-coupled transmission lines, resulting in sharp filtering selectivity, while common-mode noises are suppressed by loading the T-type stubs. A simple design method of integrating bandstop filter branches into the BPF for third harmonic suppression without increasing the circuit size is described and confirmed. A planar high-selectivity balanced BPF prototype is manufactured and measured at 2.6 GHz with a measured 3-dB fractional bandwidth of 108% to validate the framework principle. More importantly, with third harmonic suppression characteristics, the measured out-of-band rejection is more than 20 dB, spanning 4.35 GHz until 12.4 GHz.

This letter presents an improved analytical model for analyzing probe-fed microstrip antennas loaded by metallic vias with lumped terminations. The proposed formulation is based on the resonant cavity model and enables efficient analysis of such perturbed radiators for various types of terminations. The model is validated through the analysis of two antennas: one operating in a TM00 mode and the other with four capacitive terminations to produce circular polarization. Moreover, a reconfigurable RHCP/LHCP antenna based on the patch with capacitive terminations has been manufactured and tested, showing a broadside axial ratio below 0.5 dB at 1.575 GHz.

This paper presents a multibeam dielectric rod antenna for mm-wave wireless power transfer (WPT) applications. The proposed solution utilizes its unique multibeam setup which allows the generation of adjustable beams simultaneously, without the need for an additional beamforming network. To enhance the compactness of the system, each Rexolite rod is fed through an annular slot etched on a Rogers RO4003. The generated beams are steered toward the desired directions by adjustment in the configuration of these rods. The final configuration consists of five rods that were fabricated and measured. In this configuration, a beam coverage between $-30^{\circ}$ and 30∘ can be obtained, while in the frequency of interest, a gain value above $12\,\mathrm{dBi}$ is achieved. With its adjustable configuration, the proposed solution can be adapted to different operating scenarios. Moreover, the low cost and flexibility of the solution make it a promising candidate for Radio Frequency Wireless Power Transfer (RF-WPT) Internet of things applications.

This work presents the design of a wide-band frequency-selective surface (FSS) with its analysis for the performance enhancement of a microstrip antenna. To demonstrate the concept, a dual-band microstrip antenna is also designed and combined with the proposed FSS to investigate its advantages and performance enhancement capabilities. The proposed FSS is designed for a frequency range of 3.5–6.5 GHz, whereas the designed antenna operates in dual frequency bands of 3.5 and 5 GHz. The combined effect of the antenna and FSS is investigated at 5 GHz for improving the gain of the antenna from 2.8 to 3.2 dBi. The outcome of the measured performance validates that the proposed surface has potential capability for enhancing the gain of an antenna for 5G, WLAN, and Wi-Fi communication.

This paper presents for the first time the implementation of an Si/SiGe heterojunction bipolar phototransistor (HPT) into an STMicroelectronics BiCMOS technology together with the development of hydrodynamical model that fits in a trustable manner the measured opto-microwave performance. The developed hydrodynamical model relies on a precise topology analysis of the HPT and an efficient optical absorption coefficient model. It is key to predict the optimization required for the HPT. Simulation results with responsivities of 0.92 A/W and bandwidth of 1.55 GHz are obtained at low $V_{\scriptsize{\text{CE}}}=2$ V and for small devices with $2 \times 2\,\unicode{x00B5} \text{m}^{2}$ optical window. Simulation results are used to identify the best horizontal geometry that maximizes the gain–bandwidth product of the HPT. The behavior of the photo-generated carriers in the active region of the device is investigated.

We present continuous Class-F (CCF) and continuous Class-F−1 (CCF−1) power amplifiers (PAs) with compact circuit sizes. The output matching network (OMN) of a continuously harmonic-tuned PA must accommodate varying load impedance conditions across a wide frequency range, spanning from the fundamental frequency up to the 2nd and 3rd harmonic frequencies. This requirement typically leads to LPF-type OMNs with a significant circuit area overhead, thereby limiting the applicability of the broadband PAs. In this paper, we propose utilizing a one-port composite right-/left-handed transmission line to control the harmonic loads, while the fundamental loads are managed by a moderately sized LPF. This resulted in a notable reduction in PA size by nearly an order of magnitude. We demonstrate the effectiveness of this design approach through the fabrication of 2-GHz-band GaN HEMT PAs operating in CCF and CCF−1 modes. While both PAs exhibited high-efficiency (>70%) operational bandwidths at a state-of-the-art level, we also elucidate key design considerations specific to each PA operation mode.

In this article, a qualitative work has been carried out based on airborne pulsed Doppler (PD) RF sensor consist of its operational requirements in terms of phase noise modeling and associated contributing factors. Precise and efficient theoretical modeling of phase noise requirement for airborne-PD radar or long-range RF sensor is presented. This work also emphasis on the limitation of conventional phase noise modeling practices used for PD RF sensor. An improved equation has been derived for accurate phase noise estimation considering the range correlation effect and inline flicker contribution on residual phase noise requirement. Random vibrations causes increase in phase noise level around low frequency offsets region in local oscillator. The proposed phase noise model is efficient enough to counter phase noise degradation at lower frequency offsets. The proposed model is also experimentally validated. Improved modeling offers benefit in reducing the stringent RF sensor phase noise specifications at close-in frequency offsets using range correlation effect and precise inclusion of inline flicker contribution. Present work can be used to mitigate random vibration effects at close-in phase noise offsets, which avoids complex stabilization practices and stringent oscillator design phase noise specification.

We present a higher-order spectral element method (SEM) for analyzing eccentric anisotropic multilayered waveguides. The formulation uses conformal transformation optics to map the original eccentric waveguide to an equivalent concentric one. This transformation is extended to handle anisotropic non-reciprocal media characterized by non-symmetric and non-Hermitian tensors. In the transformed concentric domain, higher-order two-dimensional basis functions associated with the zeros of the completed Lobatto polynomial are used to expand the fields. To simulate radially unbounded problems, we employ a complex-stretched perfectly matched layer to mimic open space. The method is validated with radially bounded two-layer and three-layer waveguides and radially unbounded three-layer waveguides. Comparisons with the finite element method (FEM) demonstrate that our SEM approach requires significantly fewer degrees of freedom than FEM.

Reconfigurable intelligent surfaces (RISs) enhance the performance of wireless communication networks, particularly within millimeter wave (mm-Wave) bands. When a line-of-sight link is not strong enough or is fully blocked. The location of RIS has a significant impact on the RIS’s wireless channel and system performance. A wireless communication model has been proposed in a mm-Wave environment supported by RIS. The proposed model contains one transmitter and five users at the receiving end. Due to the small distance between users, there is interference between them and the received signal-to-interference-plus-noise ratio (SINR) decreases. Three RISs separated by different interspace distances were proposed to serve users at various distances from the transmitter to reduce inter-user interference. The simulation results showed that increasing the distance between the RIS site and the TX-User line served a larger number of users, and the three heights of the RIS provided a coverage range domain complementary to each other for different user sites. The improvement percentages in SINR for the second and third RIS are 48.46% and 77.38%, respectively. Enlarging the size of the RIS only increases the signal capacity and does not affect the coverage range domain of the single RIS.

This paper introduces a three-substrate layered transmitarray design that avoids the use of vias, aiming to produce broadband orbital angular momentum (OAM) vortex beams within the Ka-band. The suggested element configuration accomplishes a full 360∘ transmission phase while upholding a 1-dB transmission loss, with an overall thickness measuring 3.4 mm (equivalent to 0.34λ0 at 30.0 GHz). Its balanced unit cell arrangement amplifies its effectiveness in applications involving dual polarization. We examine the transmitarray behavior across four OAM modes (+1, +2, +3, +4 ), unveiling notable mode purity at operating frequency. Specifically, a broadband OAM vortex beam is achieved for the +1 mode during simulation. A square aperture transmitarray fed by a horn antenna is fabricated and measured to validate these simulated findings. Experimental results confirm the successful broadband vortex beam generation for $l = +1$ mode across the frequency spectrum from 27.0 to 40.0 GHz, approximately 43.3%. Additionally, the proposed transmitarray achieves a peak gain of 21.7 dBi, accompanied by an 11.8% aperture efficiency. Noteworthy is the consistent maintenance of mode purity above 86%.

In this article, we present a simulation tool for modeling a quasi-optical bench for material characterization. The model uses a Gaussian beam expansion and tracking analysis, together with a modal analysis to enable a comparison of the simulated reflection and transmission S-parameters to the ones measured with a 4-port vector network analyzer. A Thru-Reflect-Line calibration is performed to de-embed the simulated S-parameters of a dielectric slab located between two lens antennas, showing good agreement with the analytical slab model used for experimental permittivity extraction.

This paper presents a comprehensive analysis of interference events in automotive scenarios based on radar systems equipped with communication-assisted chirp sequence (CaCS). First, it examines the impact of interference on radar and communication functionalities in CaCS systems according to the orientation of the investigated nodes. For this purpose, a graph-based approach is employed with MATLAB simulations to illustrate the potential occurrence of interference on the graph for communication functionality compared with their counterparts on radar. Second, the paper delves into the impact of interference on the synchronization between two communicating CaCS nodes. It extends a previous study to match the frequency of current radar sensors, where chirp estimation, an adjusted version of the Schmidl & Cox algorithm, and correlation are adopted to synchronize the transmitter and receiver of two CaCS communicating nodes in the time-frequency plane. The proposed synchronization method is finally verified by measurements at ${79}\,\mathrm{GHz}$ with a system-on-chip, where the resulting correlation metric and mean square error are illustrated as validation factors.

A compact 8-port eighth-mode substrate-integrated waveguide (EMSIW) multiple-input multiple-output (MIMO) antenna is presented in this paper. It consists of eight EMSIW cavities placed side by side sharing their open-ended edges which are separated by rectangular slots. High isolation (>22 dB) between the antenna elements over the entire operating band is obtained by the strategic placement of rectangular slots and vias. The open-ended region of EMSIW cavity resonator and the edges of the diagonal slots help in the excitation of TE110 mode at 5.5 GHz. The simulated bandwidth of MIMO antenna is 180 MHz, while the measured bandwidth is 220 MHz. The proposed MIMO antenna system has potential applications for sub-6 GHz communication systems.

This invited, extended, paper compares and contrasts a number of different near-field (NF) to far-field (FF) transformation algorithms that can be used for the purpose of processing NF data acquired using multi-axis industrial robots. The merits and limitations of these various, commonly encountered algorithms are highlighted with comparison FF data presented across a frequency range spanning 3–15 GHz. Crucially, the paper explores the viability of using mixed mode acquisition geometries when performing antenna gain measurements where, prior to this work, several of the transforms yielded different transform gains, and electrical lengths. Here, we verify that at 8 GHz and above, where truncation effects were minimal, for a circa 30 dBi gain (at 8 GHz) test antenna the FF peaks were in agreement to better than ±0.02 dB, at 3σ irrespective of the acquisition geometry and transform algorithm used. In this invited, extended work, the existing simulation results are augmented with experimental results obtained from planar and spherical NF measurements of a pyramidal horn taken using a dual robotic antenna measurement system and a consistent distributed RF subsystem.

In this paper, a novel polarization conversion metasurface (PCM) is proposed. Compared with the conventional receiver-transmitter metasurface units, two metallized via holes are set up to correct the current. It can achieve better polarization conversion from linear to circular and maintain a high reflectivity performance. A patch antenna with an L-probe feed is used as a feeder. The circularly polarized Fabry–Perot resonator antenna (CP-FPRA) consists of the PCM with a 5 × 5 array and a feeder. The measurements indicate a 3 dB axial ratio (AR) bandwidth of 8.6% (22.3–24.3 GHz). And it achieves a maximum gain of 14.2 dBic at 24 GHz, compared to the feed antenna has a gain enhancement of 5.5 dBi (from 8.7 dBi to 14.2 dBic). The proposed CP-FPRA has high gain, a wide AR, and a relatively low profile, providing ideas for subsequent antenna designs.

In this paper, a large, compact array antenna that can be expanded in the 2-D plane is proposed for near-field radio frequency identification applications. By the introduction of the fractal structure and corner joint method, the array is easy to expand in the 2-D plane. An antenna element can be divided into a dozen or so loops, and traveling wave distribution makes sure that every loop is excited in a time period. So that a strong and uniform magnetic field could be generated in a large area. As a proof of concept, array antennas with $1 \times 8$, $2 \times 4$, and $3 \times 3$ elements are designed, fabricated, and measured. The measured bandwidth of the antennas covers the entire Chinese standard. Reading distances of the proposed large array antennas achieved up to 57 mm. Results show that the proposed antenna could realize flexibility and extendibility in a large area with stable and uniform magnetic field distribution.