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In this letter, we propose and experimentally demonstrate a space‐fed beamforming approach capable of steering beams up to ±70° with a focal ratio (F/D) reduced to 0.27 and a scan loss remained 4 dB. It is implemented based on an mmWave phase reconfigurable metasurface, and an unconventional array‐fed architecture. By doing so, while the total profile of conventional space‐fed phased arrays can be significantly reduced, specifications such as scan range and scan loss can be simultaneously improved. Compared with conventional phased array systems, such specifications are unique, and can be used to realize low‐profile, cost‐effective, space‐fed phased arrays requiring ultrawide coverages at mmWave frequencies. [ABSTRACT FROM AUTHOR]

This paper proposes a compact three-mode base station capable of performing radar sensing, communication, and wireless power transfer (WPT) in collaboration with indoor sensor networks. With regard to the wireless sensor node, the base station transmits two-tone signals in the downlink to support its operation and provides two-way communication. The sensor node sends uplink information through backscattering using the third order intermodulation (IM3) product of the rectification. In the radar mode, a single-tone continuous wave (CW) is used to monitor if there is a moving target in the static environment. If a speed is detected, the transmit signal to the node is stopped, while the single-tone CW excitation will continue until the speed of the target is zero, and then the base station transmits a stepped frequency continuous wave (SFCW) signal to measure the distance of the target. The repeat between the two radar waveforms continues until the target is undetectable within the detection range. The software defined radio PlutoSDR is adopted as the base station. The system can wirelessly supply power and bi-directionally communicate with a CO 2 sensor node 2 m away. It gives a range resolution of 2.5 cm and a minimum detectable speed of 0.25 m/s in the radar mode. [ABSTRACT FROM AUTHOR]

The occurrence of passive intermodulation (PIM) is inevitable in high-power microwave devices. It interferes with wireless communication and radar systems, resulting in severe deterioration of receiving performance. So far, narrowband PIM analyzers have been realized for different business bands. However, they are incapable of testing wideband systems. To solve this problem, rack-mounted analyzers piled with multiple narrowband analyzers were implemented. While such solutions significantly increase the volume, cost, and power consumption, they cannot provide a wide, continuous bandwidth for PIM localizations. Aiming to solve this problem, we propose a novel solution for realizing ultrawideband PIM analyzers. Based on the principle of cooperative radio frequency and baseband (RF-BB) nulling, we demonstrate an experimental prototype working within a continuous frequency band covering three octaves, exhibiting promising potential in PIM testing applications. [ABSTRACT FROM AUTHOR]

Spatial Kramers–Kronig (KK) medium provides a new platform to achieve omnidirectionally reflectionless absorption without using any gain elements. However, impedance‐matched spatial KK media realized in previous experiments generally have flat geometries with large transverse dimensions. Realizing finite spatial KK absorbers in free space background is important for many practical applications but has not been demonstrated experimentally thus far. Here, the concept of spatial KK relation to cylindrical coordinates is extended and a double‐resonance space‐frequency KK permittivity profile is implemented in a circular geometry. Omnidirectional impedance matching to free space is achieved by truncating the spatial KK absorber at the boundary where the relative permittivity is unity. For the experimental verification, a two‐dimensional 6.6‐wavelength‐diameter doughnut‐shaped anechoic chamber is implemented using the designed spatial KK medium. The measured electric field distributions and experimental imaging confirm the omnidirectionally reflectionless property, demonstrating that this miniaturized anechoic chamber is suitable for electrically small scatterer measurements and imaging. The proposed finite spatial KK absorber and fabricated miniaturized anechoic chamber show great promises for electromagnetic shielding and compatibility. [ABSTRACT FROM AUTHOR]

In this communication, we present a low-cost chipless radio frequency identification (RFID) tag with a high data capacity and a wide reading range based on time-domain scattering modulation. The proposed tag consists of a slotted square patch antenna with a switchable resistor and a mechanically driven slider etched with a barcode-like metallic wire array. Encoding is achieved by the presence and absence of the metallic wire on the slider, and tag identification is obtained by sequential bit reading. A special encoding strategy is applied to improve its insensitivity to the motion velocity of the slider. For a proof-of-concept demonstration, a prototype designed to operate at 2.1 GHz was fabricated and measured, and the experimental results verified the effectiveness. Compared with the methods based on time-domain reflectometry, spectral signature, and resonator-based sequential encoding, the proposed approach provides a substantially enhanced data capacity within a narrow spectrum without sacrificing its reading range and tag size, due to the design of nonresonant code cell. Such a mechanically triggered chipless RFID tag exhibits promising potentials in some practical applications, such as personal ID and credit cards. [ABSTRACT FROM AUTHOR]

Inspired by the envision of space solar power satellite, microwave‐based wireless power transfer has been intensively studied. To date, while significant progresses have been achieved, bottlenecks still exist. Among them, the deterioration of the radiofrequency (RF)‐to‐direct current (DC) efficiency due to the variation of incident microwave power is a major problem. It prevents this technology from many practical applications. In this work, based on the dependence between the incident power density and the resistive DC load, we propose a self‐adaptive approach to mitigate this deterioration by introducing a continuous DC load modulation. Experiments based on a complex‐conjugate rectifying surface showed effective improvements of the RF‐to‐DC efficiency for the incident power density varied in a wide range. [ABSTRACT FROM AUTHOR]

We present the experimental realization of a one-dimensional left-handed/right-handed resonator. The left-handed (LH) part of the resonator is formed by a solid-state-like metamaterial composed of [OMEGA] metallic structures, while the right-handed part is just air. The resonant behavior is successfully observed and an acceptable Q value is obtained. Through phase measurement, we verify that the LH metamaterial layer acts as a phase compensator. Further proof is given by varying the thicknesses of both layers simultaneously to achieve the same resonant frequency under the limitation of total phase difference less than 2 [pi], which is a criterion dramatically different from traditional cavity resonators. Index Terms--Left-handed metamaterials (LHMs), resonator.

Capable of remote presentations of human heart activities, the Doppler cardiogram (DCG) can be detected by an agile Doppler radar sensor. However, as a recently developed technology, its performance needs sustained improvements for the future practical applications. In this work, a continuous-wave, ${V}$ -band Doppler radar sensor was implemented to improve the discrimination of the receiver, for detecting micrometer-level details of heartbeat motions conducted to the chest skin. Besides, new algorithms were derived to achieve high linearity, to demodulate the Doppler phases and retrieve the fine details of DCG waveforms. Experimental measurements to different subjects showed significantly enhanced robustness and accuracy. The obtained results imply a promising potential of DCGs in wide application scenarios such as medical wisdom and personal healthcare. [ABSTRACT FROM AUTHOR]

Microwave imaging based on the inverse scattering problem has attracted many interests in microwave community. To obtain a satisfactory imaging quality, in most cases, a scattering-free environment is desired. In this work, to provide such an environment, we experimentally demonstrate a compact microwave imager integrated with a board-integrated, multiport vector network analyzer and a miniaturized, cylindrical anechoic chamber dedicatedly designed for inverse scattering-based microwave imaging. Based on the principle of electrically induced transparency and the effective medium equivalence, an inhomogeneous, ultrathin, dual-angle absorbing surface was designed, simulated, and implemented, to simultaneously absorb incident and scattered fields. Experimental imaging verified its effectiveness. The proposed imager would help the promotion of practical imaging, showing the potential in on-side imaging. [ABSTRACT FROM AUTHOR]

Recently, microwave imaging based on randomized illuminations has demonstrated promising potentials. The key to realize such imaging is to implement an imager with a reconfigurable, randomized aperture. In this work, we discuss the theory and the guidelines for implementing such an imager and demonstrate an experimental prototype working in the 24-GHz ISM band. It is realized with a board-integrated, space-fed, 400-element phased array capable of realizing independent 1-bit phase modulations for each element. The fields transmitting through this aperture can be deterministically randomized by simply controlling direct current bias voltages. Assisted by optimized system calibration and standard $\ell _{1}$ -norm regularization, experimental imaging with a notably improved quality can be obtained. The proposed solution can be used in wide applications, especially suitable for the massive personal security screenings in common public, government, and military areas. [ABSTRACT FROM AUTHOR]

A high‐precision differential microwave dielectric sensor system based on a pair of CSRR‐SIW resonators is introduced. The proposed method consists of four parts: the frequency‐sweeping signal source, the balanced sensor based on CSRR‐SIW, the RMS power detector, and the data acquisition system. Without a vector network analyzer (VNA) and other instruments, the electromagnetic properties of materials can be measured conveniently with the proposed method. In this work, two CSRR resonators inside SIW cavities are used as the balanced RF sensing components, one for measurement and the other for reference. In virtue of the electric field concentration effect of the CSRR and the high Q factor of SIW cavity, the proposed sensor achieves high sensitivity to material under test (MUT), with high isolation between the balanced resonators and strong capability of suppressing the electromagnetic interferences from the external environment. The resonating frequency of the balanced microwave resonator under no‐load condition is 1.587 GHz. With balanced sensor configuration, interferences from the external environment and fabrication errors for the single‐resonator‐based system can be filtered out and compensated automatically, and thus high precision of the dielectric constant measurement can be achieved. The experiment results of proposed differential dielectric sensor system validate that the measurement accuracy of the dielectric constant can reach an excellent level with a relative measurement error below 0.1%. [ABSTRACT FROM AUTHOR]

In the past decades, continuous Doppler radar sensor-based biosignal detections have attracted many research interests. A typical example is the Doppler heartbeat detection. While significant progresses have been achieved, reliable, time-domain accurate demodulation of biosignals in the presence of unavoidable direct current (dc) offsets remains a technical challenge. Aiming to overcome this difficulty, we propose in this article a novel demodulation algorithm that does not need to trace and eliminate dynamic dc offsets based on approximating segmented arcs in a quadrature constellation of sampling data to directional chords. Assisted by the principal component analysis, such chords and their directions can be deterministically determined. Simulations and experimental validations showed full recovery of micrometer-level pendulum movements and strongly noised human heartbeats, verifying the effectiveness and accuracy of the proposed approach. [ABSTRACT FROM AUTHOR]

Combining the advantages of the phase tunability provided by active frequency selective surfaces (FSSs) and the beam-steering scheme used in conventional 1-D Fresnel-zone-plate (FZP) antennas, we report in this communication a 2-D beam-steering FZP antenna that needs only 180° phase tunability. Compared with transmit arrays, while the substrate layers are reduced by a half, a phase compensation strategy is used to enhance antenna specifications. To verify the proposed approach, a radome implemented based on an active, reconfigurable FSS was designed, simulated, and experimentally implemented. With a simple three-layer structure, the implemented FZP antenna works within an ultrawide bandwidth ranging from 5 to 6.3 GHz, corresponding to a 21% relative bandwidth. With a gain up to 19.3 dBi, the scanning range reaches ±45° in both horizontal and vertical planes. This cost-effective, simple-structured antenna can be potentially used in diverse RF and microwave applications. [ABSTRACT FROM AUTHOR]

Personal devices such as smartphones and tablets are rapidly becoming personal communication, information, and control centers. Apart from multitouch screens, human gestures are considered as a new interactive human–smart device interface. In this work, we propose a noncontact solution to implement hand gesture recognitions for smart devices. It is based on a continuous wave, time-division-multiplexing (TDM), single-input multiple-output (SIMO) Doppler radar sensor that can be realized by slightly modifying existing RF front ends of smart devices, and a machine-learning algorithm to recognize predefined gestures by classifying deterministic Doppler signals. An experimental setup emulating a smartphone-based radar sensor was implemented, and the experimental results verified the robustness and the accuracy of the proposed approach. [ABSTRACT FROM AUTHOR]

To date, 3-D radar imaging of moving objects in a multipath coordinate space close to antennas remains a technical challenge. In this work, we demonstrate the implementation of such 3-D motion imaging based on a continuous-wave, multiple-input multiple-output (MIMO) Doppler radar sensor (DRS). Working with a time-division-multiplex (TDM) scheme, this portable, cost-effective DRS is a bistatic system with one transmitting and one receiving channels, and a radio frequency (RF) switch in each channel toggling between two antennas. Assisted by algorithms specifically derived for the TDM-MIMO architecture, highly sensitive 3-D imaging performed in a multipath indoor environment was experimentally implemented. Numerical simulations and experimental demonstrations verified the effectiveness and accuracy of the proposed approach. [ABSTRACT FROM AUTHOR]

Besides the prohibitive cost, complexity, and baseband scale, the development of millimeter-wave (mmWave) digital-beamforming fifth-generation (5G) frontends is facing a physical-layer challenge of thermal dissipation. This is caused by the massively integrated power amplifiers (PAs) and the extremely compact volume due to millimeter-scale wavelengths. In this work, we theoretically analyze and experimentally demonstrate a reconfigurable planar Fresnel lens, based on which a new-concept mmWave beamforming frontend can be implemented with significantly reduced number of PAs. It overcomes the inherent shortcomings of analog beamforming solutions relying on massive use of power dividers and phase shifters and can replace the convex lens used in the recently proposed hybrid beamforming solution. The implemented Ka-band lens is simple-structured, cost-effective, and easy to control, providing multiple modes for beamspace massive-multiple-input multiple-output (MIMO) communications. Experimental results verified its potential in different mmWave 5G systems such as base stations and point-to-point links. [ABSTRACT FROM AUTHOR]

Measurements of dielectric constant are of significant importance. Existing methods, contact or noncontact, require the sample under test (SUT) with a specified dimension. It can be the cross section of a rectangular waveguide or a regular-shaped reference SUT. In this work, a new approach extended from microwave imaging is proposed to remotely measure the dielectric constants of 2-D SUTs with arbitrary cross sections. An algorithm based on scattering integral equations is derived for an efficient parameter retrieval. Experimental measurements based on a time-division bistatic multiantenna system were conducted. It is verified that by deriving an inverse scattering problem-based algorithm, the dielectric constants of such SUTs can be effectively retrieved from the scattering data detected by a measurement setup previously designed for microwave imaging, regardless of the complexity of their cross sections. The proposed approach can be readily applied to various 2-D samples such as dielectric section bars. It can also be conveniently extended to 3-D samples in the future. [ABSTRACT FROM AUTHOR]

In this communication, we experimentally demonstrate a frequency- and beam-reconfigurable lens antenna based on an active second-order bandpass frequency-selective surface (FSS). The FSS lens is composed of three nonresonant metallic layers separated by two thin dielectric substrates. By integrating microwave varactors in FSS unit cells, the center frequency of this bandpass FSS can be tuned from 4.0 to 5.8 GHz by a direct-current (dc) bias voltage. Based on this wideband tunability, the phase-correction technique is used to implement a microwave Fresnel lens. The experimental results show that the proposed 1-D lens antenna can achieve frequency-reconfigurable beam steering within a 1 GHz bandwidth. With advantages of low cost and concise structure, the proposed reconfigurable lens antenna can be potentially used in a wide range of applications. [ABSTRACT FROM AUTHOR]

Induction logging through casing (ILTC) is of significant importance to the evaluation of residual oils. Traditional induction logging fails to work in cased wells due to the shielding effect of metallic casings. To date, the feasibility of ILTC remains an open question. In this article, we propose an ILTC based on the detection of lateral waves that carry the formation information. Based on the analytical equations derived to describe the hybrid modes of total magnetic fields that can be detected inside cased wells, numerical analyses aiming to describe the behavior of lateral waves were carried out in both frequency and time domains. The obtained results comply with full-wave simulations and existing scaled experiments. Our results indicate that if an ILTC tool can be properly configured to work in a region dominated by lateral waves, and the casing effect and the primary field of the lateral waves can be effectively compensated, it is feasible to implement an ILTC to detect formation conductivities ranging from 0.01 to 5 S/m. [ABSTRACT FROM AUTHOR]

Spatial Kramers–Kronig (KK) relations have been recently proposed to achieve perfect absorption without using any gain elements or highly anisotropic materials. However, such perfect absorption is limited to the surface of an infinitely long planar slab in the Cartesian coordinate, and the cases of surfaces with bends or sharp corners are still challenging. In this article, we apply conformal transformation optics methods to design spatial KK media, which can achieve smooth perfect absorption both in cylindrical spaces and in polygonal spaces with sharp corners. Moreover, it is demonstrated that we can also control the scattering direction of the designed polygonal spatial KK media to realize invisibility. Our work opens new avenues for perfect absorption devices based on transformation optics and spatial KK relations. [ABSTRACT FROM AUTHOR]

Most medical instruments invented to measure human heart activities, such as electrocardiograms (ECGs), rely on contact electrodes. This causes discomfort and limits application scenarios. Remote acquisition of $\mu \text{V}$ -level bioelectrical cardiac signals through ECG measurement is theoretically challenging. Based on the analysis of magnetic resonance imaging to the volume change of human hearts, we found that a single radar sensor can be used to remotely detect a Doppler cardiogram (DCG) at a distance up to 1 m, by retrieving Doppler signals induced by combined atrial and ventricular motions conducted to the skin of the back chest. This DCG can provide all the timing information of the P-wave, QRS-waves, and T-wave carried in ECGs. The implemented miniature remote sensor could be an ideal portable instrument for patients, such as burn victims, extending application scenarios to personal healthcare, battlefield rescue, and others. [ABSTRACT FROM AUTHOR]

The analytical description of dielectric multipactors requires an accurate physical model. In this article, a nonstationary statistical theory for the analysis of single-surface dielectric multipactors is established by defining an emission-to-emission transition rate and involving all the probability densities related to the emitted secondary electrons. Under the same conditions, the fluctuation of electrons in the evolution process of dielectric multipactors was calculated by the proposed theory and simulated by a commercial particle simulation tool developed based on the Monte Carlo analysis. The calculated results comply well with the simulated ones. Our results also indicated that to obtain an adequate accuracy, at least two random variables, the emission velocity and zenith angle, need to be considered. [ABSTRACT FROM AUTHOR]

In electromagnetics, anechoic chambers are used to obtain artificial analogs of free space. Such chambers are electrically large due to the inherent angle-dependent nature of absorbing materials. Existing models of perfectly matched layer (PML) imply that angle-independent reflectionless absorptions can hardly be achieved without involving gain media. In this paper, we mathematically derived an unconventional PML model, based on which the angle-dependent nature of absorbing materials can be manipulated to construct electrically small anechoic chambers. As an example, a semiclosed cylindrical chamber was experimentally implemented with an inhomogeneous artificial surface as thin as 0.012 wavelength. The inner diameter of this chamber is six wavelengths. The spatial voltage standing wave ratio (VSWR) experimentally measured inside this chamber complies with the theoretical analysis and full-wave simulation. With the aid of the dielectric 3-D printing technology, high-performance, microsized anechoic chambers can be constructed for scientific research and technology development in the future. [ABSTRACT FROM AUTHOR]

For a small antenna placed on a metamaterial ground plane vertically or horizontally, we analyzed the conditions under which the antenna emissions are highly directional. We found through finite-difference time-domain (FDTD) simulations that a previously discovered directional emission phenomenon can be explained by our theory for the horizontal antenna case. For the vertical antenna case, we employed FDTD simulations to design a realistic metamaterial ground plane with desired reflection phase properties, and performed microwave experiments to verify its ability to support directional emissions. [ABSTRACT FROM AUTHOR]

Surface plasmon polaritons (SPPs) propagating along a perfectly electric conducting film with an array of cut-through slits are studied analytically, and both the symmetric and asymmetric dielectric environments of the film are considered. Such a film structure, whether its substrate and superstrate are the same or different, may support a series of SPP modes, whose dispersion relations can be tailored by the film geometry. There exists a fundamental mode without any cutoff in the symmetric film structure, whereas all modes in the asymmetric structure have cutoffs, meaning that even the lowest-order mode can only exist when the film thickness is larger than a certain value. Moreover, for both types of symmetric and asymmetric film structures, the SPP bands do not overlap each other in the frequency domain, so the single-mode propagation is available for each mode. The fields of SPP modes are often highly confined to the structured film when the frequency approaches the asymptotic frequency. [ABSTRACT FROM AUTHOR]

We apply coordinate transformations in the design of waveguides with bent geometry to reduce reflection at the incident port. It was found that in the case of metallic waveguides, by applying the transformation to the medium inside a right-angle bent waveguide, low reflection can be obtained. For the case of dielectric waveguides, this can also be done by applying the same transformation to the bent region containing both the dielectric core and its claddings. Our proposed technique provides an alternative method for designing bent waveguides with low insertion loss. [ABSTRACT FROM AUTHOR]

In physics, the Brewster effect initially refers to a reflectionless transmission of a transverse-magnetic wave that impinges on an interface separating two different regular media at a particular angle, known as the Brewster angle. Nowadays, people have recognized that the Brewster effect can also be observed under transverse-electric incidences such as in magnetic media. However, all Brewster effects observed so far were associated with a unique incident angle. In this work, we demonstrate a Terahertz metasurface on which the Brewster effect can be observed at all angles of incidence. The underlying physics behind this all-angle Brewster effect is the dispersion engineered at each angle of incidence to strictly match the longitudinal wave impedance on both sides of the surface. Theoretical analysis, full-wave simulation, and experimental results are consistent with each other. The proposed approach is simple but robust and scalable to other frequencies, implying promising applications such as perfect polarizers and space phase shifters. [ABSTRACT FROM AUTHOR]

Recently, microwave imaging under random field illuminations has attracted many interests. This paper theoretically analyzes and experimentally implements a qualitative microwave radar imaging system suitable for 2-D object. It can be customized on the demands of the desired object size and imaging resolution. Based on random illuminations generated by a minimum number of antenna elements, an analytical equation can be used to reconstruct the image of the object in near real time. The simple-structured and cost-effective imaging system can be implemented in microwave, millimeter-wave, and even sub-THz frequency bands, having promising potentials for various microwave imaging applications. [ABSTRACT FROM AUTHOR]

In the past years, significant progresses have been achieved in signpost-based indoor navigation and positioning systems. In this paper, inspired by recent bionic researches on long-distance animal geomagnetic navigation, we propose an autonomous local navigation and positioning system, based on an artificially established magnetic gradient for in-grid or desktop applications. Without using any magnetic-field strength information, the proposed navigation and positioning can be accomplished by matching a spatial angle included by the direction of the vector magnetic field and a direction defined in the navigation plane using an algorithm derived based on the Kalman filter. Simulations and experiments verified the effectiveness of the proposed approach. This method can be used to improve the positioning precision of signpost-based systems. It can also be used in new applications of autonomous in-grid or desktop navigation and positioning for automatic robot arms. [ABSTRACT FROM AUTHOR]

Noncontact detection of human vital signs based on miniaturized Doppler radar systems (DRSs) can be widely used in healthcare and biomedical applications. Although significant progresses have been achieved, a reliable wireless vital signs detection in the presence of large-scale random human body movements remains a technical challenge. In this paper, based on a comprehensive use of the high-dynamic-range radar architecture and linearized Doppler phase demodulation algorithms, we further introduce matched filters to retrieve the respiration and heartbeat spectra completely concealed under the wideband noise floor caused by large-scale body movements. Along with an existing 5.8-GHz system, a single-board integrated DRS operating at 24 GHz was designed to verify the effectiveness of the used architecture and algorithms. Experimental results comply with the theoretical expectation. The obtained results imply the potential to implement practical bioradar systems for human noncontact vital signs detections. [ABSTRACT FROM AUTHOR]

Many radio frequency measurement systems require multicarrier signals with coherent phases between carriers with different frequencies. A typical example is the signal generator which is used in multicarrier multipactor (MM) testing systems. In this paper, we propose a new approach for the generation of coherent multicarrier signals based on a state-of-the-art phase-locked loops technique. Different from existing systems that rely on a heavy use of commercial microwave instruments, this generator can be implemented with on-shelf chips and devices. As an example, an ultrahigh frequency band generator is implemented and how to implement the in-system calibration of this generator in an experimental multipactor testing system is demonstrated. Based on the proposed approach, performing a quantitative experimental research on MM becomes affordable for an ordinary microwave laboratory, which may promote the in-depth experimental study in this area. It can also be used in a wide range of applications such as MIMO and phased array systems. [ABSTRACT FROM AUTHOR]

Passive intermodulation (PIM) potentially occurs in all high-power passive microwave devices. It can severely deteriorate the receiving performance of wireless communication and radar systems. To date, the simultaneous localization of multiple PIM sources in practical microwave devices is still a technical challenge. In this paper, we indicate that if a reference PIM source can be introduced into the standard PIM testing system, and the amplitude and frequency-dependent phase difference between the reference and the real PIM products can be used to construct a k-space multicarrier signal, PIM localization algorithms for both wideband and narrowband devices can be proposed based on the inverse k-space Fourier transform and inverse optimization of the partial multicarrier signal. Simulation and experimental results validate the effectiveness of the proposed approaches. These methods can solve the difficulty of multipoint PIM localization, and can be widely used in the design, production, testing, and troubleshooting of high-power microwave systems. [ABSTRACT FROM AUTHOR]

This paper presents a printed circuit board realization of a $K$ -band portable frequency-modulated continuous-wave radar transceiver with beamforming array for short-range localization. The transmitter channel of the proposed radar consists of a free-running voltage-controlled oscillator (VCO) and a single patch antenna. A linear frequency-modulated chirp signal is generated by the VCO, which is controlled by an analog “sawtooth” voltage generator. The receiver channel has a four-element linear beamforming array, a six-port circuit, and a baseband circuit. The beam of the array can be continuously steered in a range of ±45° on the $H$ -plane through an array of vector controllers. Each vector controller is capable of simultaneously controlling the phase and the amplitude of the corresponding array element. The design principle of the binary-phase-shift attenuator, the vector controller, and the radar system are discussed. Calibration method of the array is introduced to minimize the errors caused by component variation and fabrication. The radiation patterns of the array with phase-only beam steering and phase-amplitude beamforming are measured and compared, demonstrating the advantage of the beamforming design. System-level experiments showed that the proposed solution is suitable for short-range localization. In addition, experiments with a human subject revealed the capability of the proposed radar system to discriminate a human target from other objects based on the vital-Doppler effect. [ABSTRACT FROM AUTHOR]

The newly discovered “long-term” multicarrier multipactors that can be induced by low-energy electric fields potentially threatens the reliability of spaceborne microwave systems. It also causes a new technical challenge to the prediction of the global occurrence threshold of multicarrier multipactors. In this paper, we propose efficient approaches to rapidly compute the fluctuation of space electrons in the evolving process of a multicarrier multipactor, based on which Monte Carlo approaches are developed to efficiently find the global “worst case” waveforms and the occurrence thresholds for both “single-event” and “long-term” multipactors. The proposed approaches can be used for wideband devices, providing an efficient integrated solution for the multicarrier multipactor analysis for practical high-power microwave devices with inhomogeneous field distribution. [ABSTRACT FROM PUBLISHER]

We investigate a non-Foster element implemented with a radio-frequency operational amplifier theoretically and experimentally, showing that its full-range frequency response exhibits an inverted Lorentzian resonance, and thus a high-frequency non-Foster response can be observed on the right side of the resonance region. This can be used to overcome the technical difficulty in achieving high-frequency non-Foster elements. [ABSTRACT FROM AUTHOR]

Wireless localization has become a hot topic in the area of microwave engineering. In this paper, we propose a new approach for short-range wireless localization based on meta-aperture and compressed sensing (CS). Utilizing the plasmonic dispersion of a magnetically uniaxial metamaterial, a pushpin-shaped autocorrelation characteristic of the localization system can be obtained to ensure high localization precision. Compared with existing realizations based on traveling wave excited, randomly arranged subwavelength resonant elements, our method uses a homogeneous aperture for the generation of randomized illumination. Based on the CS, localization can be obtained with much less data and much faster data processing than conventional methods. Simulation and experimental investigation are conducted, and the results demonstrate the effectiveness of the proposed approach. With the simple implementation for fast localization, our method has promising potential in practical applications. [ABSTRACT FROM PUBLISHER]

This paper reviews recent progress of portable short-range noncontact microwave radar systems for motion detection, positioning, and imaging applications. With the continuous advancements of modern semiconductor technologies and embedded computing, many functionalities that could only be achieved by bulky radar systems in the past are now integrated into portable devices with integrated circuit chips and printed circuits boards. These portable solutions are able to provide high motion detection sensitivity, excellent signal-to-noise ratio, and satisfactory range detection capability. Assisted by on-board signal processing algorithms, they can play important roles in various areas, such as health and elderly care, veterinary monitoring, human-computer interaction, structural monitoring, indoor tracking, and wind engineering. This paper reviews some system architectures and practical implementations for typical wireless sensing applications. It also discusses potential future developments for the next-generation portable smart radar systems. [ABSTRACT FROM AUTHOR]