Development of large-scale quantum computing systems will require radio frequency (RF) and microwave technologies operating reliably at cryogenic temperatures down to tens of milli-Kelvin (mK). The quantum bits in the most promising quantum computing technologies such as the superconducting quantum computing are designed using principles of microwave engineering and operated using microwave signals. The control, readout, and coupling of qubits are implemented using a network of microwave components operating at various temperature stages. To ensure reliable operation of quantum computing systems, it is critical to ensure optimal performance of these microwave components and qubits at their respective operating temperatures, which can be as low as mK temperatures. It is, therefore, critical to understand the microwave characteristics of waveforms, components, circuits, networks, and systems at cryogenic temperatures. The UK’s National Physical Laboratory (NPL) is focussed on developing new microwave measurement capabilities through the UK’s National Quantum Technologies Programme to address various microwave test and measurement challenges in quantum computing. This includes the development of various measurement capabilities to characterize the microwave performance of quantum and microwave devices and substrate materials at cryogenic temperatures. This paper summarizes the roadmap of activities at NPL to address these microwave metrology challenges in quantum computing.

This paper presents a methodology designed to leverage multitemporal sequences of synthetic aperture radar (SAR) and multispectral data and automatically extract urban changes. The approach compares results using different radar and optical sensors, describing the advantages and drawbacks of using SAR data from the COnstellation of small Satellites for the Mediterranean basin Observation (COSMO)/SkyMed, SAtélite Argentino de Observación COn Microondas (SAOCOM), and Sentinel-1 constellations, as well as nighttime light data or Sentinel-2 images. Multiple indexes obtained from multispectral data are compared, too, and results obtained by an unsupervised clustering procedure are analyzed. The results show that using different datasets it is possible to obtain consistent results about different types of changes in urban areas (e.g., demolition, development, and densification) with different levels of spatial details.

Adrenal gland-induced hypertension, also known as secondary hypertension, is a medical condition caused by an underlying adrenal pathology, most typically adrenocortical adenomas. Current clinical practices involve pharmacotherapy or surgical resection to treat adrenal gland diseases that cause hypertension. However, due to the limitations of these treatment options, microwave ablation (MWA) has emerged as a promising minimally invasive alternative. An accurate understanding of the dielectric properties of adrenal glands would support the further development and optimization of MWA technology for treating adrenal tumors. Only a few studies have examined the dielectric properties of both human and animal adrenal glands, and the sample sizes of these studies have been relatively small. Therefore, further dielectric data of human and animal adrenal glands are warranted. This paper presents the ex vivo dielectric properties of the ovine adrenal glands (medulla and cortex) and summarizes the published literature on dielectric data of adrenal glands from porcine, bovine, ovine, and human samples in the microwave frequency range to analyze the consistency and reliability of the reported data. The dielectric properties of the ovine adrenal glands (N = 8) were measured using an open-ended coaxial probe measurement technique at frequencies ranging from 0.5 to 8.5 GHz. This study also investigated the temperature-dependent dielectric properties of the ovine adrenal medulla ranging from 37 to 64°C at frequencies ranging from 0.5 to 8.5 GHz. The dielectric properties of the ovine adrenal medulla measured in this study were found to be consistent with the literature. Moreover, the review suggests that variations exist in the dielectric properties of the adrenal medulla and cortex among species. The study also found that the dielectric properties of the adrenal medulla decrease with increasing temperature, similar to other tissues for which temperature-dependent dielectric data have been reported. This summary of dielectric data of adrenal glands and the temperature-dependent dielectric properties of the ovine adrenal medulla will accelerate the development of MWA technologies for hypertension treatment.

Radar absorption structures made of an active frequency selective surfaces (AFSS) have enormous potential in the aviation, naval, and other industries. In this research paper, a systematic review (SR) is carried out in the field of the AFSS to bring uncertainties, obstacles, challenges, classifications, applications, and design issues that arrive in the development of the sub-6 GHz architecture. To bias the AFSS component, as per the signal requirements, a unique set of circuits (PIN diode) is required, with ON and OFF state and a transmission zone. The bandwidth of which is determined by the bias voltage supplied. It can behave as a complicated hybrid impedance structure by providing ON and OFF biasing voltage to a PIN diode embodied in an FSS structure. Higher manufacturing costs of AFSS components, more significant complexities involved, a large amount of power consumption, and reactive impedance losses are some common limitations faced while implementing and designing an AFSS. Many envisioned problems are corrected with the AFSS design, current or creative implementations, and processing parameters are investigated progressively. It implies that new AFSSs will be an alternative to regular FSSs in the future. This paper is based on Kitchenham’s three-phase review procedure and supplements it with results, views, and recommendations from other leading experts in the field.

This article presents the design of a dielectric lens antenna that utilizes the concept of a stepped Fresnel lens for focusing electromagnetic millimeter waves. Based on the quasi-optical properties of these waves, a Cartesian Oval is optimized and employed as a focusing lens. Multiple such lenses are combined to two different Fresnel-based lens antennas. We survey these newly designed lens antennas and compare them with a focusing lens antenna based on a Cartesian oval and a far-field lens antenna. Simulations and measurements with a frequency-modulated continuous-wave (FMCW) radar validate the effectiveness of the new design, demonstrating an even improved focus size while significantly reducing the size and weight of the lens antenna by up to 53% and by nearly 48 %, respectively. Additionally, the Fresnel-based lens antennas reveal a frequency dependency, enabling frequency-based steering of the focal length over a wide relative tuning range of 177%, which we thoroughly investigate for various bandwidths and center frequencies.

In this study, a novel, cost-effective miniaturized tag antenna was developed for applications on the human body. To achieve impedance matching with the complex conjugate impedance of the Monza-4 tag chip (7.17–j74.22 Ω at 915 MHz), the proposed structure was configured by coarsely tuning the positions of vias and fine-tuning the small gaps of its coupled patches. For further reducing the profile and dimensions of the antenna, a design technique based on the three-dimensional dipole antenna current distribution was used. The proposed antenna configuration was not only miniaturized but also achieved a long stable reading distance (>5.0 m) and a wide impedance bandwidth of 71 MHz or 7.65% (covering the ultrahigh frequency radio frequency identification ranges in most regions), regardless of the location of the tag on the human body. Experiments were conducted to validate the simulated results, and adequate agreement was found between the simulated results and the measured results.

Radar-based hand gesture recognition is a potential noncontact human–machine interaction technique. To enhance the recognition performance of hand gesture, a multidomain fusion-based recognition method using frequency-modulated continuous wave radar is proposed in this article. The received raw echo data of gestures is preprocessed to obtain the range–time matrix, Doppler–time matrix, and range–Doppler–frame tensor. The obtained three-domain radar data corresponding to each gesture are input into the three-channel convolutional neural network for feature extraction. In particular, the extracted features from three-domain data are fused with learnable weight matrices to obtain the final gesture classification results. The experimental results have shown that the classification accuracy of the proposed multidomain fusion network based on learning weight matrix-based fusion is 98.45%, which improves the classification performance compared with the classic average-based fusion and concatenation fusion.

The main interest in using synthetic aperture radar (SAR) technology in automotive scenarios is that arbitrarily long arrays can be synthesized by exploiting the natural motion of the ego vehicle, enabling finer azimuth resolution and improved detection. All of this is achieved without increasing the hardware complexity in terms of the number of physical antennas. In this paper, we start by discussing the application of SAR imaging in the automotive environment from both theoretical and experimental perspectives. We proceed by describing an efficient processing workflow and we derive the rough number of operations required to focus an image proving the real-time imaging capability of the system. The experimental results are based on open road data acquired using an eight-channel radar at 77 GHz, considering side-looking SAR and forward SAR. The results confirm the idea that SAR imaging can be successfully and routinely used for high-resolution mapping of urban environments in the near future.

Frequency-modulated continuous-wave radar systems profit from increasing the absolute bandwidths of the generated frequency chirps to improve range resolution. As the relative bandwidth of SiGe-voltage-controlled oscillators (VCOs) is limited to about 80%, increasing the center frequency fundamentally or via frequency multiplication is the most direct way to increase that absolute bandwidth. However, as some applications require penetration depth, which dramatically decreases with frequency, other solutions are necessary. Therefore, state-of-the-art concepts rely on the down-conversion of generated frequency chirps via two separately stabilized frequency sources. This article implements a novel architecture, offering relative bandwidths of >100% within a single phase-locked loop (PLL). Therefore, two VCOs at different center frequencies are fed into a down-conversion mixer, whose output is directly stabilized via that PLL with one loop filter generating both tuning voltages. Those circuit blocks can be summarized as one equivalent VCO, offering a higher relative bandwidth and a significantly more linear tuning curve. Thereby, a solution to limited relative bandwidths with high VCO gain variation of single VCO synthesizers is offered while substantially reducing the hardware and implementation effort compared to the state-of-the-art.

This paper presents a low-profile six-beam antenna implemented by a compact two-layer 6 × 6 beamforming network (BFN) and a 6 × 2 slot antenna in substrate integrated waveguide (SIW) technology. The main components of the proposed 6 × 6 BFN are 3 × 3 multi-aperture couplers, interlayer hybrid couplers, and several phase shifters which are embedded on two microwave substrates. The proposed antenna has been designed, simulated, and fabricated for the frequency range of 28–32 GHz. The size of this antenna is 82 × 31.8 × 0.787 mm3, which can be a suitable choice for 5G applications due to its compact dimensions compared to similar works. Prototype testing shows that the proposed structure presents a stable beamforming performance both in simulation and measurement with good agreement. The antenna generates six radiation beams in directions ±9°, ±30°, and ±54° with good return losses and isolations.

This paper proposes a triple-band fractal slot antenna with enhanced gain operating at frequencies of 2.7, 3.5, and 4.8 GHz for microwave wireless power transmission. The antenna achieved more than 3 dB gain by preserving the symmetrical defected reflector structure behind it at a length of 0.54λ/4, where λ is the wavelength in free space at 2.7 GHz. A 50 Ω micro-strip line coupled at 66 mm length helps feed the triple band slot antenna. The purpose of a triple-band rectifier circuit with an impedance network is to convert the radio frequency (RF) signal into direct current. The measurements reveal that the antenna’s enhanced gain is 8.8 dB, and the rectifier’s highest RF signal to direct current conversion efficiency is 74.3%. For the combined configuration unit of measure, the antenna is assimilated into the rectifier via back-to-back 50 Ω Sub Miniature Version A (SMA) connectors. The highest recorded efficiency of 49.67% was obtained for the rectenna at optimum values of 1 kΩ resistive load and −5 dBm power input. It has been revealed that the rectifier-integrated antenna presented is effective for low-input RF energy capture and power transmission.

This article presents the design of a novel sigma slotted circular monopole antenna for wireless body area network applications. The design is proceeded with a sigma-shaped slot etched on the circular radiator with Rogers 4003C substrate. The size of the proposed antenna is 30 × 30 × 1 mm3. With partial ground plane, the bandwidth characteristics of the antenna have been enhanced. The designed antenna covers 2–10 GHz of the ultra wideband, thereby providing more than 106% bandwidth. The antenna exhibits high gain values of 1.95, 3.23, 3.46, and 5.95 dB at 2.45, 3.45, 5.8, and 9.5 GHz, respectively. The proposed design operates on off-body mode at 2.45 GHz and on-body mode at 5.8 GHz, thus acting as a dual-mode antenna. To ensure the health and safety measure, specific absorption rate analysis was done for both low and high values of input power and also with Cartesian and cylindrical human arm models. Bending analysis was also done. The time domain parameter group delay was also analyzed for the proposed antenna for on- and off-body scenarios. The prototype was fabricated, and validation of simulation results was done for free space and on-body scenarios.

In this paper, a mode-matching procedure is used to prove for the first time the dispersionless behavior of glide symmetry (GS) in corrugated metasurface waveguides. Depending on their field symmetry, the Floquet harmonics have a different impact onto the frequency dispersion, which is reduced with GS when the gap between the surfaces is small. Indeed, the glide-symmetric waveguide is shown to have the same effective propagation features as a scaled mirror-symmetric waveguide with half the period and a doubled gap. We propose closed-form formulas for the effective refractive index of the glide-symmetric waveguide in the first Brillouin zone, having a small groove compared to the period. The closed-form expressions analytically prove the dispersionless behavior of GS.

Single-ended and balanced 90–120 GHz microstrip power amplifier MMICs have been designed for cost-sensitive 5G and 6G backhaul in a commercial 6-inch, 0.1-µm GaAs process. At 108 GHz, measured output power is 20.4 and 22.5 dBm, respectively. At 120 GHz, measured output is 12.6 and 17.4 dBm, respectively. This is the highest reported for GaAs, among the highest reported to date for microstrip MMIC amplifiers at these frequencies and competitive with more expensive InP and GaN processes. Measurement is compared with simulation.

This paper investigates the performance of 3D-printed dielectric reflectarray antennas (RAs) with wideband behavior and beam-steering capabilities. The designed unit cell consists of a single-layer dielectric element perforated with a square hole, whose side is used to control the local variation of the reflection coefficient. The numerical analysis of the unit cell and of first $52\times52$ reflectarray working in Ka-band, whose scanning capabilities are tested just moving the feed along an arc, confirms that the unit cell has a stable behavior with respect to both the frequency and the direction of arrival of the incident field. In view of these promising capabilities, the proposed unit cell is used to design a bifocal reflectarray with the same size and working in the same frequency band of the first one. Its numerical characterization and the measurements of a prototype prove that the RA is able to provide less than 0.8 dB of gain losses over a scanning range of ±40∘ in the vertical plane, while the bandwidth varies between 13.5% and 28%, depending on the pointing direction. The obtained results demonstrate the effectiveness of the proposed approach and highlight the potential of 3D-printing technology for producing high performance, cost-effective RAs with wideband behavior and excellent beam-steering features.

Wireless power transfer (WPT) is an emerging technology with many promising applications where transmitting power via wired connections is undesirable. However, near-field WPT between magnetically coupled inductors is highly susceptible to positional changes, with power transfer efficiency (PTE) suffering if the coils are misaligned. To combat this effect, many position-independent, self-adaptive, inductive WPT schemes have been developed. Recent work indicates that it is possible to passively achieve high PTE across the operating range with nonlinear capacitors. In this work, the functionality of nonlinear WPT circuits is investigated, and fundamental design equations are derived and validated. A simplified design procedure is proposed for the position-independent self-adaptive WPT using nonlinear capacitors, wherein the ideal capacitance is extracted for each coupling factor. The efficacy of the method is demonstrated with an experimental circuit. Future work in this area is also proposed.

This research work presents an implantable antenna that operates at 5.8 GHz. By using a radiator with a loop-based design, the antenna can be made smaller. Radiator is made up of three connected rectangular loops. On the substrate’s back side, an I-shaped ground plane is used. As substrate and superstrate, polydimethylsiloxane (PDMS) with dimensions of 7 mm × 5 mm × 0.3 mm is used. The conducting sections are made using copper foil that is 30 µm thick. The suggested antenna is examined by the implantable medical device using realistic human scalp phantom models and a homogenous skin box. Simulated study revealed that it operates around 5.8 GHz with a bandwidth from 5.69 to 5.92 GHz. The specific absorption rate was 0.28 and 0.26 W/kg for skin box and human scalp phantoms, respectively, at 1 mW input power across 1 g volume tissue.

The design of low-profile Multiple-Input-Multiple-Output (MIMO) antennas for various 5G applications is a topic of huge interest in academia, research, and telecommunication sector. In this aspect, a compact and low-profile 5G MIMO antenna has been designed and analyzed for various 5G applications, specifically for the 24 GHz bands (24.25–24.45 GHz and 25.05–25.25 GHz) and local multipoint distribution system band (27.5–28.35 GHz) of the 5G spectrum. The proposed antenna structure is 20 × 20 × 1 mm3 in dimension. Two spade-shaped radiators composed of Copper (annealed) material are placed orthogonally to improve isolation and maintain signal diversity. Rogers RT 5880 is used as the material for substrate. The antenna exhibits a wide bandwidth of 21.5–28.5 GHz. The mutual isolation |S21| has been maintained ≤29 dB due to the insertion of a T-shaped parasitic strip in between the radiating elements. Novelty in design and superiority in performance has been observed when compared with related antenna categories.