This paper presents an experimental overview of linearity metrics using setups based on a PNA-X and a vector signal analyzer to evaluate key performance indicators of a transistor, such as noise power ratio and error vector magnitude, under unequally spaced multi-tone (USMT) and various quadrature amplitude modulation signals. The purpose of this study is to verify the feasibility of characterizing the linearity of transistors and RF power amplifiers on a PNA-X-based measurement bench by exploiting the statistical properties of the previously developed USMT signal, which allows NPR measurement in a single pass. The measurements were performed on an $8 \times 50\,\mu\,\mathrm{m}$ gate GaN transistor from UMS Foundry,operating on-wafer at 29 GHz.

A rigorous analysis of the scattering of plane and cylindrical waves from a strip loaded single near zero and double near zero (DNZ) metamaterial cylindrical object is presented. The proposed problem has been solved using integral equations derived from Green’s theorem and usual tangential boundary conditions. During the analysis, it was found that by loading a strip onto the metamaterial cylindrical objects, one can enhance or diminish the scattering under some specified conditions. It is shown that an enhancement in the back scattering occurs for a strip loaded DNZ metamaterial cylinder as compared to the back scattering of an unloaded DNZ metamaterial cylinder for both types of incident polarization. In the case of a specifically located electric line source, it is argued that by loading a strip onto a DNZ metamaterial cylinder, one can reduce the magnitude of the total field significantly at specific observation azimuth angles. For a specific location of a magnetic line source, the magnitude of total field of a strip loaded mu near zero (MNZ) metamaterial can be significantly enhanced as compared to unloaded MNZ cylinder in the specific observation directions. This parametric investigation is helpful in the designing of cylindrical metamaterial-based devices.

This paper presents a millimeter-wave end-fire dual-polarized (DP) array antenna with symmetrical radiation patterns and high isolation. The DP radiation element is formed by integrating a quasi-Yagi antenna (providing horizontal polarization) into a pyramidal horn antenna (providing vertical polarization), resulting in a DP radiation element with a symmetrical radiation aperture. To efficiently feed the DP element while maintaining high isolation, a mode-composite full-corporate-feed network is employed, comprising substrate-integrated waveguide supporting the TE10 mode and substrate-integrated coaxial line supporting the TEM mode. This design eliminates the need for additional transition structures, achieving excellent mode isolation and a reduced substrate layer number. A 1 × 4-element DP array prototype operating at 26.5–29.5 GHz using low temperature co-fired ceramic technology was designed, fabricated, and measured. The test results indicate that the prototype achieves an average gain exceeding 10 dBi for both polarizations within the operating band. Thanks to the symmetrical DP radiation element and mode-composite full-corporate-feed network, symmetrical radiation patterns for both polarizations are observed in both the horizontal and vertical planes, along with a high cross-polarization discrimination of 22 dB and polarization port isolation of 35 dB.

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.

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 research presents the design and development of a microwave sensor capable of detecting and distinguishing hydroxylated organic compounds (HOCs), namely water, methanol, ethanol, and propanol. The work analyzes the physical mechanisms that govern the sensitivity and detectability of these liquids in the microwave range. Differences in sensor response are linked to variations in molecular characteristics such as dipole moment, microwave absorption, and refractive index. Unlike approaches that rely solely on experimentation, this study connects microwave behavior to fundamental molecular properties, enabling a predictive, physics-based understanding of HOC detection. Molecular polarization and relaxation models were combined with experimental observations to explain how these compounds interact with microwave fields. A metamaterial-based sensing cell was designed, simulated, and experimentally validated. Results demonstrate that the sensor effectively identifies hydroxyl compounds with high sensitivity. Water produced the highest resonance-frequency shift (0.76 GHz), followed by methanol (0.7 GHz), while ethanol and propanol showed similar shifts around 0.35–0.37 GHz. Propanol achieved a quality factor of 10.82 in the 12–17 GHz range. The sensor also reached a frequency detection resolution of 6.75 MHz and showed strong amplitude sensitivity, highest for water at 10.66 dB.

This research introduces a cutting-edge approach to glucose monitoring, which is essential in many applications. The study developed a new non-invasive glucose monitoring system utilizing machine learning techniques. This system examines the reflection coefficient data gathered from glucose solutions using a Vector Network Analyzer. To showcase the system’s accuracy in predicting glucose levels, two distinct datasets were employed. The first dataset comprised glucose solutions with concentrations spanning from 0 to 200 g/L, while the second dataset included solutions ranging from 15 000 to 20 000 mg/L for enhanced precision. The system measured both datasets, and three machine learning algorithms – Decision Tree, Random Forest, and Support Vector Regression – were applied to the collected data. Furthermore, a grid search method was employed to optimize the hyperparameters for each model’s optimal performance. The findings revealed that the Random Forest yielded the best results across both datasets. For gram scale, the R2 value was 0.9995, indicating that 99.95% of the glucose level variance was accounted for, with a low RMSE of 1.1589 mg/dL. Moreover, in milligram scale dataset, the R2 value was 0.9932, and RMSE was 1.1119 mg/dL, confirming the model’s high accuracy. These experimental outcomes demonstrate that the proposed system can effectively predict glucose levels.

Intelligent Reflecting Surface (IRS) technology operating at mm-wave frequencies is promising for 6G applications. However, this technique faces the challenge of beam splitting, as beams cannot be directed accurately at all frequencies. To enhance system performance and lessen the beam spillting effect, the IRS is developed using phase shifters and time delay modules, as the problem is analyzed in this paper. The results of the simulation revealed that the proposed system, which is based on sub-surface IRS and time delay modules, successfully overcomes the packet splitting challenge effectively. The proposed architecture was 94.5% better in gain compared with the traditional architecture. The results explained a 54% improvement in data rate when time delay is used in the Phase-shift-Time delay-Phase delay (PTDP) system compared to the conventional design. Moreover, the use of 2-bit phase shifting alone in the proposed design was appropriate to realize close to optimal performance due to the system capability to direct power in the desired direction through the use of precoding technology, which compensates for losses resulting from beam splitting.

A long-range, compact, wideband Ultra High Frequency (UHF) radio frequency identification (RFID) tag is proposed. The design features a triangular patch, designed to achieve wideband impedance matching. The tag exhibit −10 dB bandwidth from 753 to 917 MHz with a substrate thickness of 1.575 mm. The overall size of the tag is 121 × 30 × 1.575 mm3. The gain and bandwidth for varying substrate thickness is investigated. Further, two parasitic strips are designed alongside the patch to operate the tag more effectively at Federal Communications Commission (FCC) band in simultaneous with European Telecommunications Standards Institute (ETSI) band with increased read range. With parasitic strips, the tag exhibits −10 dB bandwidth from 766.5 to 896.5 MHz and 905 to 943.6 MHz which covers the bandwidth requirements in Europe, Asia, and North America. A prototype of the proposed tag is fabricated and experimentally tested with the RFID Higgs 4 IC. The tag provides a read range of over 14 m in 865–870 MHz and 13 m in 902–928 MHz when the tag is operated in free space and a read range of over 10.2 m in 865–870 MHz range and 10.3 m in 902–928 MHz range when mounted on a metallic surface of size of 200 × 200 m2 . The performance parameters of the designed tag are also compared with some commercially available designs.

This paper presents a wideband dual-polarized in-band full duplex antenna which can also suppress the higher order modes. A dual differential capacitive feeding scheme is proposed to increase the isolation between the co-located transmitter and receiver ports. The proposed design uses λ/4 resonators in close vicinity of the radiating patch to provide spurious-free characteristics. Further, a parasitic patch placed above the radiating patch at height “h” is used to enhance the input matching, impedance bandwidth, and gain of the proposed design. The key features of the proposed structure are its wide impedance bandwidth (∼20%), high inter-port isolation (>58 dB) throughout the entire operating frequency range (2.26–2.76 GHz), and simultaneous suppression of higher order modes which makes it a suitable candidate for modern wireless application. Finally, a prototype is fabricated and measurement results are in good agreement with simulation results.

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 article presents germanium telluride (GeTe)-based switches for radiofrequency (RF) applications, capable of reversible switching between their ON and OFF states through optical activation by irradiation. Unlike previous studies, the transition is induced by infrared laser pulses at a wavelength of λ = 915 nm, which is highly promising for future integration of laser sources and the proposal of fully integrated optical activation of phase change material (PCM) switches. This represents a novel approach compared to the existing literature, which primarily focuses on the ultra-violet spectrum, less suitable for on-chip optical integration. Our work also provides combined optical and thermal simulations to elucidate the challenges associated with actuating small PCM switches and demonstrates the effectiveness of PCMs at this wavelength. The study achieves bistable switching at high frequencies up to 40 GHz, with a figure of merit of 31.5 fs, despite the low GeTe conductivity of only 1.85·105 S/m. Additionally, significant advancements over the literature have been made by surpassing 30,000 cycles with optical actuation.

This paper presents a flexible SiGe monolithic microwave integrated circuit (MMIC) chipset for 120 GHz ultra-wideband frequency-modulated continuous wave radar systems. The highly integrated chipset is implemented with multiple-input and multiple-output radar in mind which leads to transmit and receive MMICs with four integrated channels in each chip. The transmitter achieves an output power of 12.9 dBm with a total power consumption of only 403 mW. The receiver chip incorporates a sub-harmonic approach for suppression of leakage radiation at 120 GHz through a receive channel. Both chips integrate active multiplier chains that are driven by a third reference dual band voltage-controlled oscillator (VCO) MMIC that can deliver an output at center frequencies of 15 or 30 GHz. The reference VCO MMIC demonstrates relative tuning ranges of 32%.

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.

The design of filters used in waveguides, which are crucial components of high-frequency communication systems, plays a significant role in improving system performance. In this study, the usage of metamaterials is first proposed, the SLA 3D printing method is used to design and fabricate CSRR meta-resonators-based bandpass waveguide filters (WGFs) with different filter orders for C-band (4-7.5 GHz), and simulated and measured filter performances are compared. Since the proposed novel WG structure is modular, it allows the design of C-band WGFs using different thicknesses of substrate materials. Also, the number of unit elements can be increased and any number of meta-resonators can be inserted to design filters of different orders ranging from 1 to 5. The electrical length of the WGF/WG structure can be changed according to the needs of the applications. The resulting WGFs demonstrated superior RF performance, being 50% lighter than comparable models found in the literature. Over the relevant frequency range, the filter exhibited return losses between 31-43 dB, insertion losses from 0.1 to 0.35 dB, FBW ranging from 12% to 16%, and quality factors between 6.23 and 8.28, depending on the filter order. The obtained experimental results align closely with the simulation predictions, confirming the effectiveness of the design.

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.