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A feasibility study on the compensation of 3D mispositioning errors of the probe occurring in the characterization of a long antenna, via a non-redundant (NR) near to far-field (NTFF) transformation with helicoidal scan, is conducted in this article. Such types of errors can result from imperfections in the rail driving the linear motion of the probe and from an imprecise synchronization of the linear and rotational movements of the probe and the antenna when drawing the scan helix. To correct them, an approach, which proceeds through two steps, is proposed. The former step uses a technique called cylindo rical wave (CW) correction for compensating the phase of the near-field (NF) samples, which, owing to the rail imperfections, result in not being acquired over the measurement cylinder surface. The latter exploits an iterative scheme to restore the samples at the sampling points required by the adopted NR representation along the scan helix from those obtained by applying the CW correction technique and impaired by 2D mispositioning errors. The so compensated NF samples are then effectively recovered via a 2D optimal sampling interpolation (OSI) scheme to accurately obtain the input data required to carry out the standard cylindrical NTFF transformation. The OSI representation is determined here by assuming a long antenna under test as enclosed in a prolate ellipsoid or cylinder ending into two hemispheres (cigar) in order to make, depending on the particular geometry of the considered antenna, the representation effectively non-redundant. The reported numerical simulation results show the capability of the proposed approach to compensate even severe 3D mispositioning errors, thus enabling its usage in a real measurement scenario. [ABSTRACT FROM AUTHOR]

In this study, a millimeter-wave far-field range antenna measurement system is proposed for W-band monopulse antenna measurements. Since the W-band monopulse antenna installed in radar systems has many input/output ports, multiple calculations are required to measure all the ports. We propose a system structure capable of the simultaneous measurement of multiple channels to quickly and accurately measure the performance of a monopulse antenna. The proposed measurement system includes a multi-channel rotary joint, a pair of diplexers, and multiple vector network analyzer extenders. In addition, an RF sub-system is implemented to reliably measure the phase of the W-band radiation pattern. It utilizes a shared local oscillator source and external power amplifiers for the transmit and receive paths. Employing the proposed multi-channel antenna measurement system, the sum/difference channels of a monopulse antenna were simultaneously measured according to the azimuth angle. In addition, a comparison of the far-field measurements provided by the proposed system and the near-field measurements was conducted. [ABSTRACT FROM AUTHOR]

Breast cancers can appear and progress rapidly, necessitating more frequent monitoring outside of hospital settings to significantly reduce mortality rates. Recently, there has been considerable interest in developing techniques for portable, user-friendly, and low-cost breast tumor monitoring applications, enabling frequent and cost-efficient examinations. Microwave technique-based breast cancer detection, which is based on differential dielectric properties of malignant and healthy tissues, is regarded as a promising solution for cost-effective breast tumor monitoring. This paper presents the development process of the first proof-of-concept of a breast tumor monitoring vest which is based on the microwave technique. Two unique vests are designed and evaluated on realistic 3D human tissue phantoms having different breast density types. Additionally, the measured results are verified using simulations carried out on anatomically realistic voxel models of the electromagnetic simulations. The radio channel characteristics are evaluated and analyzed between the antennas embedded in the vest in tumor cases and reference cases. Both measurements and simulation results show that the proposed vest can detect tumors even if only 1 cm in diameter. Additionally, simulation results show detectability with 0.5 cm tumors. It is observed that the detectability of breast tumors depends on the frequency, antenna selection, size of the tumors, and breast types, causing differences of 0.5–30 dB in channel responses between the tumorous and reference cases. Due to simplicity and cost-efficiency, the proposed channel analysis-based breast monitoring vests can be used for breast health checks in smaller healthcare centers and for user-friendly home monitoring which can prove beneficial in rural areas and developing countries. [ABSTRACT FROM AUTHOR]

Emerging data processing techniques brought back into attention the HF range communication as an interesting alternative to third-party solutions for IoT applications, such as data transmission in distributed energy production facilities. The physical size of HF antennas, often comparable to the surrounding objects, require in situ radiation measurements resulting in site-customized antenna design and positioning, and consequently in a higher reliability of such HF grid communications. Drone-borne measuring systems are already known as a flexible solution, but are mostly restricted to higher frequency ranges where full-wave, wide-band probes are feasible. In this work, we propose to use an electrically small, folded dipole as a probe for drone-borne measurements on HF antennas. We also propose a calibration approach for the effects related to the near-field zone, and to the drone body proximity; corrections on these two effects are the key methodological steps. We show that despite a realized gain figure in the order of −20 dBi, such a probe can provide stable results for near-field measurements, even at input power levels as low as 1 mW. Compared to other similar approaches, our configuration provides a wider frequency band of operation, higher stability in terms of pattern diagram, and a lower cost. [ABSTRACT FROM AUTHOR]

The paper proposes a novel procedure and the corresponding mathematical method to measure the polarization characteristics of a planar wave. The method is intended and described as a method for measurement of an antenna of unknown polarization using dipole-like linearly polarized antenna in far field zone of the measured antenna. The procedure consists of only three amplitude measurements using the linear-polarized antenna in three positions, followed by a specific mathematical transformation of the obtained values into polarization parameters – axial ratio and polarization ellipse main axis tilt angle. This mathematical transformation is one of the key contributions of the presented work. It is based on the decomposition of a wave into two circularly polarized waves and on the representation of the electric field as a vector whose components are complex numbers. Furthermore, the novelty of the proposed method is that only three measurements taken at arbitrary angles of the measuring antenna are sufficient to calculate the polarization ellipse parameters. This can have practical advantages, since this method does not require expensive phase measurements and lengthy phase calibrations. If beside axial ratio and polarization ellipse tilt angle also the sense of elliptical polarization is of interest, a simple supplement method is suggested. A potential impact of noise and interference presence during measurements on the applicability of the method in certain cases is thoroughly explained. A supplement method is needed in some of such cases which is explained in detail and the appropriate procedure given.

This paper proposes a novel approach for fast human exposure absorbed power density assessment, based on a combination of over-the-air radiative field measurements and full-wave electromagnetic simulations. This so-called augmented OTA technique relies on the computation of an equivalent source or digital twin, which reproduces the radiation properties of the device under test. At short separation distances, the interaction between the human model and the device is however not negligible. A novel solution to model the influence of multiple reflections is introduced, where the inside of the equivalent source box is partially filled with a perfect electric conductor, thereby creating a reflective digital twin model. Simulation and measurement results demonstrate the relevance of this technique for enabling accurate absorbed power density evaluations. A discussion on aspects influencing the measurement time and uncertainty is also provided, where a new demonstration is delivered how spatial-averaging contributes positively to the accuracy of the method.

Breast cancers can appear and progress rapidly, necessitating more frequent monitoring outside of hospital settings to significantly reduce mortality rates. Recently, there has been considerable interest in developing techniques for portable, user-friendly, and low-cost breast tumor monitoring applications, enabling frequent and cost-efficient examinations. Microwave technique-based breast cancer detection, which is based on differential dielectric properties of malignant and healthy tissues, is regarded as a promising solution for cost-effective breast tumor monitoring. This paper presents the development process of the first proof-of-concept of a breast tumor monitoring vest which is based on the microwave technique. Two unique vests are designed and evaluated on realistic 3D human tissue phantoms having different breast density types. Additionally, the measured results are verified using simulations carried out on anatomically realistic voxel models of the electromagnetic simulations. The radio channel characteristics are evaluated and analyzed between the antennas embedded in the vest in tumor cases and reference cases. Both measurements and simulation results show that the proposed vest can detect tumors even if only 1 cm in diameter. Additionally, simulation results show detectability with 0.5 cm tumors. It is observed that the detectability of breast tumors depends on the frequency, antenna selection, size of the tumors, and breast types, causing differences of 0.5–30 dB in channel responses between the tumorous and reference cases. Due to simplicity and cost-efficiency, the proposed channel analysis-based breast monitoring vests can be used for breast health checks in smaller healthcare centers and for user-friendly home monitoring which can prove beneficial in rural areas and developing countries.

The radiometric calibration technique of spaceborne synthetic aperture radar (SAR) aims to establish a constant relationship between the SAR target pulse response energy and the actual radar cross-section (RCS) of the ground. It is an essential technology for achieving quantitative observations of the Earth using radar. In this article, the process of in-orbit radiometric calibration campaign for the SuperView Neo-2 SAR satellite is introduced, which is the distributed X-band SAR satellite in the new generation of Chinese SiWei commercial remote sensing satellite system. More specifically, the initial step involves deriving the total transfer function of the SAR system using the radar equation and establishing a stable calibration constant model for the SAR system. Further, by using the obtained calibration constant to invert the RCS value of the corner reflectors in the Otog Banner calibration field, while validating and analyzing the absolute radiometric accuracy. Considering that the elevation antenna pattern (EAP) predominantly affects the consistency of image radiometric correction, the method of extracting EAP and beam center bias angle from the rainforest is presented. Finally, the quality validation of impulse response function is performed over the California calibration field, which can effectively guarantee the quality of SuperView Neo-2 SAR satellite products. [ABSTRACT FROM AUTHOR]

In this paper, we present a systematic approach for the development of application-specific antennas for 5G millimeter-wave (mmWave) base stations. First, an in-depth analysis of 5G mmWave base stations considering the required antenna gain and antenna elements to address different equivalent isotropic radiated power requirements is presented. This is followed by an evaluation of the realistic impact of different factors, which affect mmWave communication, namely output power of power amplifiers, antenna gain, losses and weather condition (rain), on transmission ranges between base station and terminals, considering the link budget analysis for an Urban Macro cell with the Non-Line-of-Sight transmission, as an example. Finally, based on a comparative analysis of published dual-band dual-polarized 5G mmWave antennas, we propose a novel configuration of a dual-band dual-polarized antenna for 5G mmWave base station applications, which overcomes the limitations of conventional antennas in published literature. Our proposed antenna covers the specified 3 GHz bandwidths in the 5G mmWave n257 and n260 bands and reaches approximately 6 and 6.7 dBi, respectively in these bands. Furthermore, it exhibits at least 20 dB isolation between the polarizations and has dimensions of 1.8 3 1.8 3 1.2 mm. We modeled, simulated, fabricated, measured and analyzed this new antenna configuration. Excellent correlation is obtained between measurement and simulation results. [ABSTRACT FROM AUTHOR]

This research presents a small, compact microstrip patch antenna of multiband antenna. The multi-band antenna can be scaled to higher frequencies, making it possibly useful in 5G applications. The antenna is made up of asymmetric scalene triangles slots on the right side of the patch, which is provided by the reference patch antenna. The modes of antenna, patch and slots are excited to obtain four bands. The antenna design is 25×25×1.4 mm3 resonant at 3.93 GHz, 4.25 GHz, 5.37 GHz, and 6.18 GHz. The simulated design shows a peak gain of 4.44 dB at 3.93 GHz, 5.63 dB at 4.25 GHz, 5.91 dB at 5.37 GHz and 5.2 dB at 6.18 GHz. The Total efficiency at 3.93 GHz and 4.25 GHz is -1.152 dB and -0.5174 dB, at 5.37 GHz and 6.18 GHz shows a total efficiency of -0.535 dB and -0.566 dB. Finally, the antenna is fabricated and measured. A good agreement shown between measurements and fabrication in terms of return loss. [ABSTRACT FROM AUTHOR]

Wet antenna attenuation (WAA) can cause significant overestimation of rainfall estimates from commercial microwave link (CML) data. Typically, WAA estimation is done by comparing CML rainfall estimates to reference data and attributing the residual to WAA. Due to the different spatio-temporal integration characteristics of CML and reference observations this does not allow a confident conclusion about the temporal dynamics of WAA. In this work, we present the world’s first in situ WAA estimation for CML antennas, accompanied by sequences of images of the antennas as provided by our dedicated field experiment ATTRRA2. We show examples of surprising temporal dynamics, namely delayed wetting and strong WAA decrease during rainfall events. These results will support the future development of improved WAA estimation models, while, at the same time, highlighting the challenges any modeling approach will face due to the complexity of temporal WAA dynamics. [ABSTRACT FROM AUTHOR]

This letter pays attention to the mitigation of the radio frequency interference (RFI) sources located at coastal regions for synthetic aperture interferometric radiometer (SAIR). To remove an RFI at the visibility level, it will be necessary to estimate the brightness temperature (BT) of the point source, which is currently done by computing the median of the surrounded pixels to get the background BT and subtracting it from the original contaminated BT. However, this strategy is based on the assumption that the background BT distribution around the RFI is flat, and this is not reasonable for those RFIs from coastal cities and could result in estimation deviation. A robust RFI mitigation method is proposed without introducing complex computing. Instead of focusing only on the local area, the basic idea of our method is to step into the wide area and minimize the overall fluctuation of the pixels affected by the RFI in the BT image. The method tests based on SMOS visibility samples validate the correctness of the developed method. [ABSTRACT FROM AUTHOR]

The estimation of the interferometric vertical wavenumber over sloped terrain is an integral step for many interferometric and tomographic synthetic aperture radar (SAR) applications. The state of the art for this estimation is to calculate the angle of incidence and the local terrain slope after geometric corregistration has been performed. In this letter, an alternative approach for estimating the vertical wavenumber is proposed that requires only the estimation of the range corregistration shifts. This considerably simplifies the calculation effort without compromising the estimation performance. The proposed approach is demonstrated on Advanced Land Observing Satellite (ALOS) phased array L-band synthetic aperture radar (PALSAR) data and compared against the conventional methodology. [ABSTRACT FROM AUTHOR]

Polarimetric Global Navigation Satellite System-Reflectometry (GNSS-R) is the next natural step for land monitoring using GNSS signals. The Soil Moisture Active Passive (SMAP) radar receiver has been retrieving polarimetric GNSS-R data using two orthogonal linearly polarized antennas since 2015, enabling the study of the polarimetric signature of GNSS-R signals on different Earth’s surfaces. Currently, new instruments and missions are using circularly polarized antennas to retrieve polarimetric GNSS-R information. In this manuscript, synthetic right and left-hand circularly polarized signals are reconstructed using the Stokes parameters of the SMAP L2C GNSS-R data. The signal-to-noise ratio (SNR) of the SMAP-R data at the equivalent RHCP, LHCP, H, and V polarization antennas is retrieved, and normalized to an arbitrary receiver with a noise figure of 2 dB. Appling the Albersheim model, we analyze the probability of detecting a reflection in a 0.5° Lat/Lon box. Results are presented for different configurations of coherent and incoherent integration times and antenna gains, for each possible antenna polarization. We present different receiver configurations capable of detecting more than 70% and 90% GNSS reflections over land. Results show that with a 10-dB antenna and a receiver with a coherent integration time of 4 ms, and an incoherent integration time of 1000 ms would suffice to detect 19.4%, 92.3%, 83.5%, and 79.4% for RHCP, LHCP, H-polarized, and V-polarized antenna, respectively. Detectability improves up to 57.4%, 99.3%, 96.3%, and 96.6% using a 14-dB antenna. Results are then generalized to L1 C/A GNSS-R signals. [ABSTRACT FROM AUTHOR]

This paper proposes a tunable antenna based on graphene for future wireless communication technology. The proposed antenna that is made by graphene/polyimide film able to tune the frequency using thermal that is exposed on it. The approach is investigated since it able to work as the other reconfiguration technique but cannot be adjustable likes diodes and liquid crystal. The antenna is fabricated into fifteen similar pieces and are separately cured at different temperature and exposure time; 250 °C, 300 °C, and 350 °C, for 20 minutes, 30 minutes, 1 hour, 2 hours, and 3 hours. The fabricated antennas are measured its S‐parameter as well as the characterisation of relative complex permittivity, sheet resistance, conductivity, surface morphology, and structure analysis. The measured results indicate that the frequency is tuned to lower within 4.1 GHz at 250 °C, 5.5 GHz at 300 °C, and 400 MHz at 350 °C. Looking into the future, even though this work is not using the same antenna, but it will lead to the proof of concept for tunable graphene antenna using thermal at fifth generation (5G) and next generation. [ABSTRACT FROM AUTHOR]

Prototype measurements are the key step in the development of antenna structures. Typically, their far-field characteristics are validated in expensive, dedicated facilities such as open range sites, or anechoic chambers. Despite being necessary for obtaining high-precision data (e.g., for device qualification), the use of costly infrastructure might not be fully justified when the main goal of measurements includes demonstration of the methodology behind determination of the performance figures of interest (e.g., for the purpose of teaching), or rough validation of the EM simulation model correctness. From this perspective, systems for far-field measurements in non-anechoic environments represent an interesting alternative to the utilization of the state-of-the-art equipment and facilities. Despite their proven usefulness, the mentioned systems are normally constructed around the expensive, laboratory-grade equipment, which contradicts the whole concept of low-cost measurements. This paper discusses a cost-efficient, mobile system for experimental validation of antennas. Its main components include the in-house developed rotary heads, an open-hardware-based vector network analyzer, and the measurements post-processing software. The cost of the system amounts to only around 3630 USD. The capabilities of the device have been demonstrated through measurements of two antenna structures. The considered performance figures include radiation pattern and single-direction gain vs. frequency. Comparisons against the measurements performed in benchmark conditions (anechoic chamber), as well as using professional network analyzer have also been provided. Furthermore, the documentation that facilitates the construction of the system components is shared in an online repository.

This paper presents results for active and passive measurements using a novel method based on multiple compact antenna test range (CATR) reflectors to perform simultaneous multiple angle measurements in order to characterize the beam-forming characteristics in a real environment of the 5G devices operating in the millimeter wave frequency band: 24–44 GHz. The over-the-air (OTA) system generates four planar wavefronts with different incidence angles, realizing up to five pairs of angular spreads or four switched/simultaneous angles of arrival. The initial target application is radio resource management (RRM) testing, where the execution of mobility procedures and radio link monitoring of a 5G millimeter wave device are evaluated. The applicability of the multi-reflector approach to RRM testing is measured with commercial 5G handsets, through three test scenarios. The paper demonstrates that baseband (non OTA) testing is not sufficient for RRM FR2, as the results are influenced by the direction of arrival of the signal. It is further shown that OTA testing in a multi-reflector CATR system and a careful selection of a representative set of test directions is critical for full characterization of the performance of a wireless device operating in the millimeter wave bands. [ABSTRACT FROM AUTHOR]

In this brief, we propose a dual-mode power divider (PD) based on slow-wave SIW structure. The slow-wave structure is integrated to the SIW for obtaining filtering feature and a multifunctional PD with both in-phase and out-of-phase responses is designed by adopting different feeding mechanism. Then, the presented PD is applied to build a monopulse antenna with simple structure. A tapered patch is inserted into the center of the PD and excited through coupling for endfire radiation. When the PD works in in-phase mode, the even-mode E-field can be obtained at the end of radiator, resulting in the difference beam. When the PD works in out-of-phase mode, the odd-mode E-field can be obtained at the end of radiator, leading to the sum beam. The proposed monopulse antenna was fabricated and measured for validating the feasibility of the design approach. Measured results indicate that the sum and difference beams of the antenna are both realized in the same frequency range. This approach provides a straightforward way to design monopulse antenna, which can be applied in radar detection and tracking. [ABSTRACT FROM AUTHOR]

This letter presents a dual-polarized low-profile linear phased array antenna design achieving one-dimensional wide-angle scanning with high polarization isolation. The dual-polarized antenna is constructed based on a metasurface serving different purposes for two polarization cases to achieve high polarization isolation while providing a low profile as a whole. It works as artificial magnetic conductor for x-polarization and radiator for y-polarization. To achieve wide-angle scanning, surface wave effect is exploited for x-polarization while for y-polarization widebeam active element patterns is implemented with a small array spacing of 0.42 λ0 applied. To verify the design, a 1×8 linear array was fabricated and tested. Measured and simulated results both demonstrate that, within a wide operating band, the proposed dual-polarized antenna has a high port-to-port polarization isolation over 29 dB with a low profile of 0.06 λ0. The measured results show that for x-polarization, the linear array can steer its main beam up to 81°, while for y-polarization, it can steer the main beam up to 70°. The cross-polarization levels can maintain below −20 dB during scanning in the general. [ABSTRACT FROM AUTHOR]

In this letter, a transparent ultrawideband (UWB) halved coplanar Vivaldi antenna (HCVA) with metal mesh film (MMF) is proposed. Based on the equivalence principle, the halved type antenna is achieved by replacing a radiation fin with the ground plane. The proposed HCVA has the advantages of UWB impedance matching, miniaturized aperture size, high directivity, and simple feed structure. By employing MMF with a low sheet resistance of 0.35 Ω/sq and high optical transmittance above 72% in the radiation fin and ground plane, the antenna is entirely transparent. An example transparent HCVA is fabricated and measured. According to the simulated and measured results, most of the reflection coefficient is below –10 dB from 0.78 to 20 GHz. Moreover, the peak realized gain reaches 10.4 dBi with the compact size of 0.32×0.47×0.052λL3, where λL is the wavelength at the lowest operating frequency. [ABSTRACT FROM AUTHOR]

The scanning rate of a composite right/left-handed (CRLH) leaky-wave antenna (LWA) is usually determined by the dispersive behavior of the corresponding CRLH unit cell. In this letter, a novel CRLH unit cell with high dispersive behavior is proposed and investigated. The unit cell is formed by four stubs embedded in a rectangular ring patch, which is grounded with several metal vias. The right-handed characteristic is enhanced by the ring patch, while the left-handed characteristic is reduced by the vias and the gaps between the patch and the stubs. Then, the unit cell is applied to design an LWA with high scanning rate. The measured result shows that the seamless scanning angle of the antenna prototype is 130° (−65° to +65°) within a frequency range from 9.3 to 9.93 GHz (i.e., 6.6% for fractional bandwidth). Therefore, the proposed LWA antenna is with a high scanning rate up to 19.7°/%BW. [ABSTRACT FROM AUTHOR]

This letter shows a comparative analysis between the conventional and reverberation chamber (RC) measurements of error vector magnitude (EVM). The conventional methods, including direct link (DL) and anechoic chamber (AC), have been used to measure EVM for several years. However, the over-the-air testing of devices under test (DUT) is emphasized, and the EVM measurement in RC is a difficult question. For mass production testing, instead of using two chambers (RC and AC), it is expected to integrate EVM testing into the existing RC measurement system to give a pass/fail conclusion quickly. Hence, we measured EVM in 2 GHz (2412 MHz) and 5 GHz (5180 MHz) using RC, AC, and DL methods. From the measurement results, we find that the measured EVM is repeatable, stable, and insensitive to the location of DUT. Besides, the measured EVMs obtained from all scenarios deteriorate with the decrease of received power. Comparing the results from RC with that from the conventional methods, it could be concluded that with the reduction of multipath effect, the measured EVMs approach to the ideal values measured in AC. The differences among the methods could be used to calibrate the measured EVMs and give a pass/fail conclusion efficiently for mass production. [ABSTRACT FROM AUTHOR]

In this letter, a method named double phase-compensation is first proposed to drastically reduce the profile of traditional transmitarray antenna (TA) based on ray tracing principle. Previously, the folded transmitarray antenna (FTA) has realized the profile reduction to 1/3. It is known that there is an urgent need for more compact antenna nowadays. If the FTA's profile is further reduced, the focus-to-diameter (F/D) ratio should be decreased which will result in obvious aperture efficiency reduction. To further reduce the FTA's profile with unchanged F/D for keeping high efficiency, the extra phase compensation is innovatively added on the FTA's reflector. Hence the TA's profile can be reduced to lower than 1/3 and be flexibly adjusted as needed. Three FTA models are designed for comparison and demonstration. The simulation and experimental results indicate that the extra phase compensation successfully alleviates the efficiency drop caused by directly reducing the profile of FTA. Significantly, the method provides an efficient approach to further improve the compactness of antenna system and is very meaningful for TA miniaturization. [ABSTRACT FROM AUTHOR]

In this letter, a fast multinull steering technique is demonstrated by a linearly polarized linear antenna array. The new technique is based on the electric fields generated by each antenna element on a far-field arc of the antenna array, which are extracted in advance by simulation or measurement. The power transmission efficiency is used as the performance index to control the pattern nulls. By solving a matrix eigenvalue equation, in which the matrix is made up by selecting the corresponding electric fields on different positions on the arc standing for the null directions, the eigenvector corresponding to the zero eigenvalue is identified and used as the optimized distribution of excitations (ODEs) for the antenna array. Single-null and multinull patterns are tested from the ODEs and the results indicate that the number and directions of the multiple nulls can be controlled in the elevation space. The simulated and measured 2-D null patterns are shown in good agreement. [ABSTRACT FROM AUTHOR]

This letter presents the design, analysis, and measurement of a miniaturized ($\text{7}\!\times\!\text{7.5}$ mm) electrically small helical dipole antenna with the introduction of a flexible magnetic sheet of high permittivity and permeability for biomedical implants. The proposed helical dipole, operating at 402–405 MHz Medical Implant Communication Services (MICS) band, supports wider bandwidths (10 dB bandwidth: simulated 33 MHz; measured 49.5 MHz) compared to the state-of-the-art designs. In addition, as a hybrid between a magnetic loop antenna and an electric dipole antenna and operating in the normal mode with small radian (ka < 0.36), enhanced radiation efficiency has been achieved as a result of the magnetic sheet. Measured in-body to on-body transmission verifies the antenna performance. [ABSTRACT FROM AUTHOR]

This letter presents a single-layer, wide-angle, low-cost frequency beam scanning leaky-wave antenna (LWA) based on spoof surface plasmon polaritons (SSPPs). Here, two rows of Sierpinski prefractal parasitic patches are placed near an ultrathin planar SSPP waveguide, which can achieve continuous backfire to nearly endfire beam scanning with increasing frequency. The overall width of the proposed antenna is only 0.75 $\lambda _{\text{0}}$ (with $\lambda _{\text{0}}$ being the wavelength of the lowest operating frequency). This SSPP LWA provides high-performance backfire and broadside radiations due to applying prefractal units. Simulated results show that the proposed SSPP LWA achieves a wide scanning range from −90 $^{\circ }$ to +58 $^{\circ }$ within the frequency range of 3–8 GHz. The average gain and radiation efficiency of the antenna are 10.9 dBi and 88%, respectively. An antenna prototype is fabricated and measured. The measured results agree reasonably well with the simulated ones. [ABSTRACT FROM AUTHOR]

This letter presents a planar inverted-F antenna (PIFAs) system for Wireless Fidelity 6 (Wi-Fi 6) and Wi-Fi 6E applications with compact size and high isolation. To realize decoupling in a guided way, single-mode structure is proposed based on common mode and differential mode theory. For the demonstration, the mutual coupling between two back-to-back asymmetric PIFAs was reduced by etching two slots on the ground. The measured results show that the two PIFAs, respectively, achieve the impedance bandwidth of 5.14–6.03 GHz and 5.90–7.24 GHz, and the port isolation higher than 17.4 dB across 5.14–7.24 GHz frequency band. [ABSTRACT FROM AUTHOR]

This letter presents a multiantenna system with several superiorities of compact structure, high isolation, and low profile, which can be applied as a millimeter-wave sensor. The proposed multiantenna system includes three probe-fed patch antennas, which are integrated in a limited aperture (1.2·λ0 × 1.2·λ0, λ0 is corresponding to the center frequency at 24.1 GHz). Although the antennas are tightly arranged, high-isolation performance between each two antennas (> 25 dB) is achieved by rotating the antennas by 45° and introducing an X-shaped decoupling structure. Including with the impedance matching layer for measurement, the total thickness of the proposed antenna system is just 0.056·λ0, which is convenient for the integration with radio-frequency integrated circuits. The impedance matching layer is designed as a coplanar-waveguide-transition between the feed probe and the connector for multiantenna measurement in such a compact space. For demonstration, the proposed multiantenna system is fabricated and measured. The good agreement between measurement and simulation guarantees the promising application of this design for radar sensing. [ABSTRACT FROM AUTHOR]

This letter proposes a wideband high-gain left-/right-handed circularly polarized (L/RHCP) patch antenna using a mirror flip approach. The antenna consists of a ring-shaped metal square patch with truncated corners and a two-port feed network in a simple construction. The dual-port feed and truncated corners realize a wide axial ratio bandwidth (ARBW). Moreover, the L/RHCP is easily changed by mirroring the flipped feed network without redesigning the overall topology. The impedance bandwidth (IBW) (S11 < −10 dB) of 58.6% (2.97–5.43 GHz)/47.6% (2.8–4.55 GHz) and 3 dB ARBW of 44.3% (3.09–4.85 GHz)/34.6% (2.96–4.2 GHz) are achieved for L/RHCP antenna. Finally, two prototypes were fabricated and measured for validation. The proposed L/RHCP patch antenna was found to be insensitive to feed position. The IBWs of the proposed LHCP and RHCP antennas showed a wide degree of overlap. The low profile, high gain, small size, and higher robustness of our antenna than traditional patch antennas demonstrate the advantageous of our design for communication, power transmission, and medical fields. [ABSTRACT FROM AUTHOR]

This letter proposes a new ultrahigh frequency (UHF) flexible planar biconical antenna design method for partial discharge (PD) detection in gas-insulated switchgear. Continuous transverse branching increases the electrical length to expand the bandwidth and miniaturize the antenna. For comparison of the effects of the lateral branch structure model, the optimized dimensions of both designed antennas are 150×150 mm, and both use polydimethylsiloxane, flexible material with a thickness of 0.5 mm, as the substrate. The results show that the S11 of the antennas is less than −10 dB in the bands of 0.3–0.5, 0.64–1.25, and 1.4–3.0 GHz, and the planar biconical antennas still maintain good bandwidth and gain under different bending radii of 0, 150, 350, and 500 mm. The PD test platform was built to test the antenna. The experimental data show that the two flexible antennas designed in this letter can detect the PD-radiated electromagnetic wave signal with a discharge of 15 pc before and after the bending deformation and meet the UHF partial discharge detection requirements. [ABSTRACT FROM AUTHOR]

A broadband circularly polarized metasurface antenna with low radar cross section (RCS) is proposed. Four metasurface elements are arranged orthogonally in a 2×2 array and fed with a 90° phase difference to achieve circular polarization radiation. Each metasurface element is a nonuniform subarray of 4×4 metallic patches. Attributed to the nonuniform property of the metasurface element, two characteristic modes with different resonant frequencies but with similar surface current distributions are formed. By optimizing the geometric parameters of the nonuniform element, the two modes are merged with each other, resulting in bandwidth (BW) broadening of the proposed antenna. Simulated and measured results show that the designed antenna has a −10 dB impedance BW of 49.60%, 3 dB axial ratio BW of 33.13%, and peak gain of 13.17 dBic. Moreover, the RCS reduction is higher than 6 dB in the entire operation frequency band. Additionally, the antenna has a low profile of 0.08λ (λ is the free-space wavelength at an operation frequency of 8.25 GHz). [ABSTRACT FROM AUTHOR]

A low-profile broadband double-layer microstrip antenna is presented for green mobile communications. Eight solar cells are adopted for the top radiation structure, which can also improve the antenna performance. The antenna height is 0.071 λ0 (λ0 is the wavelength of 2.2 GHz in free space) with a measured −10 dB bandwidth from 1.65–2.76 GHz, so the mobile communication band from 1.71 to 2.69 GHz has been covered. Boresight radiation patterns are realized with an average gain of 8.27 dBi and measured radiation efficiency of more than 80% within the target band. This dual-function device can be a competitive candidate for green low-carbon communication systems. [ABSTRACT FROM AUTHOR]

A planar dual circularly polarized (CP) broadband array is proposed in this letter. The antenna consists of two semicircular patches and two suspended metal posts. According to the investigation of our previous work, the circularly polarized mode generated by combining the patches and the metal posts can achieve very wideband CP radiation. In order to achieve dual CP radiation with similar performance, a new antenna element is proposed with a centrally symmetrical configuration. The orthogonally crossed slot etched on the substrate-integrated waveguide cavity is used to excite the antenna element. A 4×4 array is designed, fabricated, and tested. Measured results show that a 3 dB AR bandwidth of 28.28% (26–34.6 GHz) and 30.61% (26–35.4GHz) is achieved for left-handed CP (LHCP) and right-handed CP (RHCP) radiation, respectively. The 3 dB gain bandwidth of 22.81% (26.4–33.2 GHz) and 24.50% (26–33.26 GHz) for these two polarizations is obtained. The proposed array demonstrates the feasibility of dual-polarized radiation. It features the advantage of wide bandwidth, easy integration, and low cost, which is very suitable for millimeter-Wave system applications. [ABSTRACT FROM AUTHOR]

In this letter, a power harvester with a Schottky diode and a photodiode has been designed to harvest ambient radiofrequency (RF) and solar power in a cooperative way. The RF power is collected by a coplanar waveguide-fed circularly polarized antenna operating in wifi band and converted into the dc one by a rectifying circuit composed of the Schottky diode, and meanwhile the solar energy is harvested by the photodiode to bias the Schottky diode in the rectifying circuit. With the RF and solar power simultaneously injecting into the rectifying circuit, the resulting power conversion efficiency is greatly increased for the same RF and solar power levels in a range from −20 to 0 dBm. The prototype of the proposed harvester is fabricated, and the measured results demonstrate a maximal total PCE of 73% and a maximal output power of 1450 μW. [ABSTRACT FROM AUTHOR]

In this letter, two compact, colocated, low-coupled, quad-polarized (QP) antennas are proposed based on two dual-mode radiation bodies to achieve compactness and high isolation. The first antenna obtains four polarizations by orthogonally placing two dual-mode loops; the second antenna includes a dual-mode loop and a miniaturized dual-polarized patch based on fractal structures inside the loop. To investigate the performance of QP multiple-input–multiple-output (MIMO) systems, channel parameters including correlation coefficients, degree of power balance, and channel capacities are analyzed based on the measured data. Results show that, high channel capacities can be achieved both in a realistic office room and a rich scattered reverberation chamber, which are very close to that of the 4 × 4 independently identically distributed (i.i.d.) Rayleigh channel. It is revealed that both correlation coefficient and degree of received power balance have strong influence on the performance of a MIMO system, which are related to the radiation properties of the antenna and the polarimetric characteristics of the propagation environment. [ABSTRACT FROM AUTHOR]

The ultra-wideband (UWB) technology has been widely used in high-accuracy localization systems benefiting from its superior time-resolution and stability. In recent years, the single-anchor localization (SAL) scheme has attracted intense interests with its high accuracy, low system complexity, and low deployment costs compared to traditional UWB localization schemes. In this paper, we develop a SAL system which achieves 3D high-accuracy localization using time and wrapped phase measurements of UWB signals. We expand the array aperture to improve the localization accuracy and address the phase wrapping problem using information fusion. Statistical characterization of ambiguous position estimates is encapsulated by soft positional information (SPI), which is approximated by Gaussian mixture model (GMM) to accelerate the filtering process. The parameters of GMM are estimated by an efficient parallel algorithm and two filtering methods are proposed to track the agent in different scenarios using approximate SPI. Finally, we implement the system on a low-cost platform and experimental results show that the proposed SAL system can achieve decimeter-level 3D localization accuracy in outdoor and indoor environments. [ABSTRACT FROM AUTHOR]

A one-port near-field antenna measurement technique with a small wire scatterer is proposed. In the proposed technique, a wire scatterer is scanned with an interval of less than a quarter wavelength, and the measurement is performed at the port of the antenna under test (AUT). A two-dimensional phase unwrapping method is used to remove 180° phase uncertainty. The data obtained in the near-field are transformed to the far-field pattern, and the scattering pattern is compensated for better measurements. The proposed measurement technique was validated by measuring the near-field of an AUT over a planar scanning surface. The far-field radiation pattern obtained using the proposed technique was compared with that obtained from a conventional commercial anechoic chamber. It was observed that they agreed well, especially in the region near the center.

Microelectronic probes with the ground-signal-ground (GSG) tips have been widely used in testing integrated circuits and antennas. Yet, the radiation from probes has been rarely studied, which has been found to degrade the testing accuracy of the radiation from an antenna. In this paper, a typical ACP40-GSG-100 probe is studied from both simulation and measurement. It is confirmed that the probe radiation is caused by current on its tips, the metal probe shell strongly affects the radiated power distribution, and the ignorance of probe radiation causes error to the realized gain calculation. It is found that the probe shows a symmetrical radiation pattern for its symmetrical current distribution on the tips, the matched probe has larger realized gain than the open-ended one for about 4.8 dB because of stronger current, and the different contact positions on an impedance standard substrate (ISS) make the radiation distribution be different but hardly affect the realized gain. The strongest radiation of the probe basically locates within a narrow region near the symmetry plane of the probe, which makes it easier and faster to find the peak gain. A simple mathematical model is given to explain why low-gain probes are preferred in antenna radiation tests.

The problem of detecting defective turned-off elements in antenna arrays from near-field measurements is addressed. In particular, the focus here is to reduce the number of measurements in order to positively affect the acquisition time. Such an issue is achieved by adopting the recently developed warping sampling method. Two commonly antenna diagnostics methods, i.e, the Back Transformation Method (BTM) and the Matrix Method (MM), are considered in view of this new sampling strategy and compared to the usual half-wavelength sampling. In particular, in order to identify the fault locations, outcomes returned by BTM and MM undergo a detection step based on a cell-averaging CFAR (CA)-CFAR technique borrowed from the radar literature. It is shown that the warping sampling method provides performance close to the uniform half-wavelength one with a reduced number of data. Numerical simulations are carried out in order to verify the results with different fault layouts and tapered currents.

A horizontal planar scanner with an approximate size of 40 m $\times40$ m has been implemented using the Unmanned Aerial Vehicle (UAV) technology. The UAV is not wired to the ground to maintain the flexibility and short setup time of a non-tethered flight. In this configuration, the UAV-mounted continuous-wave source is not phase-locked to the on-the-ground receiver. A dual-polarized reference antenna placed on the ground is hence used to retrieve the relevant phase information. The presented approach has been applied on the Pre - Aperture Array Verification System (Pre -AAVS1) of the Square Kilometre Array, which is a digital beamformed array with 16 active elements. An inverse source technique has been applied on measured Near-Field (NF) data acquired on two different sets of points (one for each electric field component) from all the receiver channels. In this way, Embedded Element Patterns (EEPs), array calibration coefficients and pattern have been determined from NF data only. The achieved results have been validated using a complementary set of Far-Field (FF) measurements and simulations.

Automotive sensors are essential to autonomous driving, which performs various functions to perceive the surrounding environment. Among the various functions of the automotive sensors, the estimation of vehicle orientation is considered significant in responding to unpredictable situations in a dynamic driving environment. In this article, we propose a method of estimating the vehicle orientation using a cascaded multiple-input multiple-output (MIMO) frequency-modulated continuous-wave (FMCW) radar system. The radar signal is collected by varying the orientation angle of the vehicle, and the point cloud data corresponding to the vehicle are extracted through signal preprocessing. Because the processed point cloud data are distributed along the axis of vehicle orientation, the orientation angle can be estimated by applying regression algorithms. We used the principal component analysis (PCA), decision tree, and convolutional neural network (CNN) algorithms for regression and compared their performances. The comparison of various estimation methods showed that the proposed method of using the CNN framework can accurately estimate the orientation angle of a vehicle within a root mean square error (RMSE) of 4°. [ABSTRACT FROM AUTHOR]

A periodic frequency-scanning one-dimensional microstrip leaky-wave antenna with circular polarization is proposed in this letter. The introduction of the novel square patch and stub, which are printed on the same layer of the microstrip array, can effectively transform the polarization type into left-handed circular polarization (CP). The two parasitic elements in each unit cell can be excited by the host meandering microstrip line without extra feeding networks, which introduce one orthogonal polarized wave to satisfy the condition of CP radiation. A prototype includes nine modified unit cells is fabricated and measured. The designed antenna covers an impedance bandwidth over 26.1% with |S11| < −10 dB and a CP bandwidth over 11.2% with |AR|< 3 dB in the measurement. The main beam scans from −4° to 18° in the yoz plane (beam scanning plane) through broadside direction (0°) while maintaining good CP property. [ABSTRACT FROM AUTHOR]

This letter proposes a self-deployable circularly polarized (CP) stacked Yagi–Uda phased antenna array operating at C-band (5.6–6.0 GHz). The proposed antenna system is composed of a 2×2 stacked CP Yagi–Uda antenna array and feeding networks consisting of a reflection-type phase shifter and a four-way Gysel power divider. The proposed phased antenna array is integrated into the top side of a 1U (10 $ \times $ 10 $ \times $ 10 cm3) CubeSat via fully three-dimensional (3-D) printed self-deployable spring hinges and frame. The volume of the proposed antenna is reduced by 69% when folded, and the antenna deploys to the desired shape without any actuators or power. The designed reflection-type phase shifter has 0°–373° analog phase-shifting range and the four-way Gysel power divider feeds each of the 2 $ \times $ 2 antenna array. The proposed self-deployable phased antenna array has 13.5 dBic left-handed circular polarized gain and +/−10° beam steering angle. [ABSTRACT FROM AUTHOR]

For fifth-generation (5G) millimeter-wave (mmWave) beamforming, a fully planar 2 × 2 2-D multibeam antenna operating at 24–28 GHz is proposed. The proposed antenna is fed by a compact dual-layer 4 × 4 Butler matrix in substrate-integrated waveguide (SIW). In this fully planar and compact configuration, SIW coupling slot is used to facilitate the output ports of the Butler matrix on the same planar layer, and the via-based phase shifters are designed to generate wideband phase performance with compact size. The measured impedance bandwidth is 15.4%, and the measured maximum beam pointing angle is 55°. These results are in good agreement with simulation. The proposed configuration can be extended with more radiating elements for higher gain, and it is promising for beamforming scenarios, including communications. [ABSTRACT FROM AUTHOR]

A miniaturized, vertically polarized (VP), pattern switchable/beam-steering antenna based on a metamaterial radiator is presented for sub-6 GHz applications. Different from the traditional split-ring resonator (SRR), the proposed T-shaped SRR can work as a miniaturized VP omnidirectional radiator. To steer the radiation beam, a novel switchable mushroom reflector with a low profile and low loss is explored and utilized. Multiple switchable mushroom reflectors are loaded around the T-shaped SRR radiator to obtain various steerable beams. To verify the proposed design principle, a VP beam-steering SRR-based antenna with a compact size of 0.36 λ0 × 0.36 λ0 × 0.07 λ0 is designed by loading four mushrooms. By controlling the off/on states of four switches, the proposed reconfigurable antenna can realize beam-steering in the horizontal plane (eight states with 45°-step). The measured overlapped −10 dB impedance bandwidth is wider than 3.40–3.80 GHz (11.1%), and the realized peak gain is larger than 5.3 dBi. Therefore, the proposed antenna is a good solution for the widely deployed fifth generation (5G)-NR and smart antenna applications due to its compact size, flexible beam-steering capacity, broad bandwidth, and good scanning coverage. [ABSTRACT FROM AUTHOR]

This letter presents a scalable multipolarized planar phased array for the low earth orbit satellite communication application. A dual-polarized aperture-coupled patch element antenna is proposed for designing the array, which can provide dual-linear polarization (LP) and dual-circular polarization (CP). The rotated feed technique is adopted to reduce the cross-polarization level. By using 8-channel beamformer chips and the multilayer printed circuit board technology, a phased array prototype with good electromagnetic shielding performance, high integration, and low cost is designed, fabricated, and measured. For dual-LP radiation, it steers up to the scan angles (±50°) with a scan loss less than 3.5 dB, and a cross-polarization level lower than −30 dB in azimuth/elevation plane and −15 dB in diagonal plane. For dual-CP radiation, it steers up to the scan angle (±50°) with a scan loss less than 3 dB and an axial ratio less than 3 dB. The phased array developed in this letter can be scaled to larger arrays and provides feasibility for the production of low-cost phased arrays. [ABSTRACT FROM AUTHOR]

Because the width of antenna elements exceeds half of the air wavelength, resulting in too large element spacing, the scanning angle of traditional endfire circularly polarized (CP) antenna array is usually less than 60°. In order to solve the above problem, a CP quasi-Yagi antenna element is proposed in this letter, whose width is less than half of the air wavelength. Further, an 1 × 8 endfire CP antenna array is designed. Because the element spacing is about half a wavelength, the scanning angle of the proposed endfire CP antenna array can reach 60°. Moreover, the axial ratios of all beams are less than 3 dB in the scanning angle range of (0°, 60°). The final measured results are basically consistent with the simulated results [ABSTRACT FROM AUTHOR]