Jia-Lin Li

In human detection, radar-based contactless detection by Doppler signals becomes popular in applications. A novel screw antenna array structure integrated with a 3D-printed case is proposed for this radar-based detection for human vital signs. The proposed antenna is integrated with a patch array antenna, screws, a metal plane, and a 3D-printed case. Although the screw is drilled into the patch, the integrity of the radiation pattern is maintained. Different resonant frequency can be tuned by different sizes of screws. The metal plane reduces the back lobe of the screw antenna and increases antenna gain. Compared with the traditional patch array antenna, the proposed antenna array provides a broader bandwidth, i.e., from 23.1–24.2 GHz to 22.1–25.8 GHz. In addition, gain is improved from 7.6 dBi to 8.9 dBi. When the proposed antenna array sensor is used in healthcare applications such as ISM band radar application, the overall performance shows a slight improvement compared to the traditional one. The proposed antenna array’s performance used in human vital signs is studied and compared with the traditional application.

The existing dual-band high-gain antennas based on metasurface (MS) have a common limit that the frequency ratios cannot be flexibly designated while the dual-band performances cannot be controlled independently. Here, a method to solve this problem is proposed; it adopts the concept of hybridizing a folded reflectarray and a Fabry-Pérot cavity antenna for high-gain dual-band operations. Different from previous works, the two antennas share a common aperture but are separated structurally by a polarization-selective surface (PSS) that enables dual-band independent control and flexible frequency ratios. A prototype antenna is thus developed and experimentally examined, and the measured results agree well with expectations.

In this letter, a fan-shaped aperture modulated metasurface antenna (MMA) is proposed for straight-line flat-top beamforming at a specified elevation angle. The desired beam pattern is decomposed into multiple adjacent sub-beams, implemented via a multi-beam shared-aperture technique. Unlike conventional circular or rectangular apertures, the fan-shaped design effectively suppresses beam splitting within a 7% relative bandwidth. Mushroom-shaped electromagnetic bandgap (EBG) structures are introduced at the aperture edges to reflect surface waves, thereby reducing sidelobes. Global optimization of the unit cell geometries further enhances antenna gain, achieving a uniform flat-top pattern. A prototype operating at 15 GHz demonstrates a measured peak gain of 17.3 dBi with a flat-top pattern having a 2 dBi gain variation range of about 45°, showing good agreement with the simulation results.

This study presents the design and implementation of a double-sided parallel-strip line (DSPSL) filter with an inserted conductor plane for the contactless detection of solute concentration in liquid solutions. Traditional methods of measuring concentration often involve direct interaction with a sample, which can lead to contamination. Conversely, the proposed DSPSL filter allows noninvasive measurements by placing the solution above the sensing side of the filter and this proposed filter is an insertion loss-based sensor. The design incorporates an inserted conductor plane that creates a 180° phase difference between the top and bottom networks, resulting in an effective band-stop filter configuration. When the concentration of the analyte decreases, the dielectric constant of the solution correspondingly increases, which affects the filter response. Furthermore, this study focuses on the filter’s ability to detect varying concentrations of solutions, with a glucose solution as the experimental result, demonstrating notable frequency-shift responses when samples with concentrations ranging from 10% to 50% are loaded onto the sensor. The sensitivity of the DSPSL filter to changes in the dielectric properties indicates its potential for accurate concentration measurements. The results revealed a linear relationship between the dB(S₂₁) and the glucose concentration in the solution. A mathematical sensing model was also developed via regression analysis relating the glucose concentration to the measured dB(S₂₁) level.

Wireless power transfer has become a trending research area for remotely transferring power. This paper presents the numerical simulation study of selective wireless power transfer to closely spaced wireless sensors embedded in reinforced concrete. A selective microwave wireless power transfer is achieved at a 10 mm separation between tightly-coupled monopole antennas (wireless sensor antennas). Both tightly-coupled wireless sensors operate at 2.45 GHz, hence beating the diffraction limit at λ/12 with the incorporation of additional scatterers in the reinforced concrete environment. The main objective is to realize selective wireless power transfer to wireless sensors with subwavelength separation (closely spaced) to which one makes the power request. Here, the presence of meta-structures creates some randomness serving as scatterers in the use of the electromagnetic time-reversal technique which enhances the spatial refocusing beyond the diffraction limit. This implies that the focal spot is less than half of the carrier wavelength at the operating frequency. At any time that one of the tightly-coupled sensor antennas sends a power request, power will be transferred to it alone. Cases of dry concrete with and without reinforced bars have been studied with electromagnetic time-reversal techniques for the closely spaced sensors embedded in concrete.

A reconfigurable antenna with unidirectional and bidirectional radiation patterns is proposed in this letter. An open-ended waveguide (OEWG) antenna serves as the feeding source to excite the Fresnel zone plate lens above it. Further, an anisotropic polarization-sensitive metasurface (MS) is placed at the end of the feeding antenna and parallelly to the Fresnel lens to manipulate the reflected waves from the lens. By mechanically rotating the feed orthogonally, the two radiation modes can be alternated. The proposed antenna operates at the central frequency of 28 GHz. The forward transmitted waves are in the boresight direction for both operation modes. The backward reflected wave for the bidirectional mode has a 90° polarization rotation and an elevation angle of −150°. The measured peak gain for the unidirectional mode is 20.3 dBi and those for the bidirectional mode are 16.7 dBi and 14.8 dBi for the transmitted and reflected beams, respectively. The measured gain difference for the bidirectional mode is less than 2.96 dB from 26.5 GHz to 29.5 GHz while the gain fluctuation is small for both modes within the operation band, indicating good performance.

A fan-shaped multibeam antenna based on metasurface (MS) lens is first proposed and validated in this letter. It features stable radiation gain and high beam-crossover levels that are attractive in high-quality beam-scanning applications. A simple multi-port pillbox antenna is employed as the source antenna, while an MS lens is placed above it with an air gap for beamforming. The proposed MS antenna targeting 5G millimeter-wave band has a −10-dB impedance bandwidth from 26.9 to 29.9 GHz. It can generate 5 beams with a scanning range of ±30°. Remarkably, the beam-crossover levels are higher than −1.9 dB at the central frequency. The gain variation for each beam is within 1 dB for a 12° coverage range and 3.5 dB for the whole ±30° angle coverage range. Compared with previous reports, the proposed MS antenna shows great advantages in terms of electric performance and physical properties.

A waveguide attenuator is developed for millimeter-wave system test applications. It is realized based on a standard WR6 rectangular waveguide; the substrate of the attenuator is quartz while the resistance element is the use of lossy material. A 15-dB attenuator is designed and validated from experiments.

This study presents a broadband and high efficiency hybrid inverse continuous filtering power amplifier (FPA) based on a terminated coupling line structure. The proposed FPA uses coupling lines as the main transmission line, and loading different stubs can simultaneously achieve input matching and output matching bandpass filtering. The four generated transmission zeros achieve good filtering performance. After discussing the matching structure, a broadband filtering PA operating at 1.7–2.4 GHz was designed and optimized. The measurement and simulation results showed good consistency. The best performance of the proposed PA was achieved at 2.1 GHz, with a gain of 11.24 dB, a saturation output power of 41.9 dBm, and a drain efficiency of 70.5%. The rejection of low and high frequency bands exceeds 49 and 55 dBc. The filtering PA has advantages in broad bandwidth and good out‐of‐band suppression.

In this paper, we study meandered topologies of a dual-mode loop resonator for microwave multiplexer applications. Compact channel filter structures that characterize controllable transmission zeros locating simultaneously at the lower stopband or upper stopband are, for the first time, investigated for such a kind of resonators and based on this, a microstrip triplexer is proposed. The studied triplexer uses one of the filter structures to realize the middle channel, and the rest structure to realize the upper and lower channels. The center frequencies of the three channels are 1.8 GHz, 2.0 GHz and 2.2 GHz, and the 3-dB fractional bandwidths are 3.6%, 3.6% and 4.1%, respectively. The developed triplexer features high channel-isolations of over 40 dB as a result of the controllable transmission zeros of the channel filters.