In this paper, the design, simulation andmeasurementof a dual-band polarizationinsensitive metamaterial inspired microwave absorber are presented.The unit cell is composed of two concentric closed ring resonator(CRR) structures forming octagonal rings which arecarved on an FR-4 dielectric substrate to give maximum absorption at dual frequencies of 2.09 GHz and 2.54 GHz. At these frequencies, the minimum reflection coefficients of -29.15 dB and -18.76 dB are achieved with absorption rates of 99.88% and 98.67% andnarrow 10 dB bandwidths of 2.62% and 2.76%, respectively. Microwave absorption property of the proposed absorber structure is simulated by setting the perfect electric boundary conditions in four planes whose surface normal vectors are directed perpendicular to the wave propagation direction. These numerical computation settings replicate the rectangular waveguideto be used in the experimental measurements for the comparison between the simulated and experimental results. It is experimentally verifiedby the waveguide measurement method that the absorption rates about 99% are achieved for dual bands with polarization insensitivity, thereby meeting the absorption requirements of LTE-band frequenciesfor a real time microwave absorber based energy harvesting systems.

The distorted Born approximation (DBA) of volume scattering was previously combined with the numerical solution of Maxwell equations (NMM3D) for rough surfaces to calculate radar backscattering coefficients for the Soil Moisture Active Passive (SMAP) mission. The model results were validated with the Soil Moisture Active Passive Validation Experiment 2012 (SMAPVEX12) data. In this paper, we extend the existing model to calculate the bistatic scattering coefficients for each of the three scattering mechanisms: volume, double bounce and surface scattering. Emissivities are calculated by integrating the bistatic scattering coefficients over the hemispherical solid angle. The backscattering coefficients and emissivities calculated using this approach form a consistent model for combined active and passive microwave remote sensing. This has the advantage that the active and passive microwave remote sensing models are founded on the same theoretical basis and hence allow the use of the same physical parameters such as crop density, plant height, stalk orientation, leaf radius, and surface roughness, amongst others. In this paper, this combined active and passive model is applied to four vegetation types to calculate both backscattering coefficients and brightness temperature: wheat, winter wheat, pasture and canola. This model uses a single-scattering and incoherent vegetation model, which is applicable for the vegetation fields studied in this paper but not suitable for vegetation types where collective scattering or multiple scattering effects are important. We demonstrate the use of the DBA/NMM3D for both active and passive using the same input parameters for matching active and passive coincident data. The model results are validated using coincident airborne Passive Active L-band System (PALS) low-altitude radiometer data and Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) data taken during the SMAPVEX12 field campaign. Results show an average root mean squared error (RMSE) of 1.04 dB and 1.21 dB for backscatter at VV and HH, respectively, and 4.65 K and 6.44 K for brightness temperature at V-pol and H-pol, respectively. The results are comparable to those from the tau-omega model which is commonly used to compute the brightness temperature, though the physical parameters used in this model are different from the empirically adjusted parameters used in the tau-omega model.

A frequency reconfigurable patch antenna is proposed. The antenna has a rectangular patch with two meandered slots. It can be switched between four bands using two PIN diodes by altering current distribution across the slot edges. The overall dimension of the antenna patch is 11.51 mm × 8.37 mm and fabricated on an FR4 substrate. The design is investigated by simulation and measurement, and the result includes S11 parameters, radiation patterns, measured directivity and gain. With different combinations of PIN diode biasing conditions, the antenna can be set to 6.80 GHz, 7.34 GHz, 7.80 GHz and 8.18 GHz, which collectively covers a continuous frequency range of 1.80 GHz (- 10 dB band width). The antenna also shows consistent radiation patterns at all the reconfigured frequency bands with an average beam width of about 75°. In the accessible frequency range an average gain of 5.14 dBi and low level of cross polarizations are also recorded. A good agreement between measured and simulated results validates the presented concept of frequency reconfiguration.

We propose a novel numerical approach for the optimal design of wide-area heterogeneous electromagnetic metasurfaces beyond the conventionally used unit-cell approximation. The proposed method exploits the combination of Rigorous Coupled Wave Analysis (RCWA) and global optimization techniques (two evolutionary algorithms namely the Genetic Algorithm (GA) and a modied form of the Articial Bee Colony (ABC with memetic search phase method) are considered). As a specic example, we consider the design of beam deflectors using all-dielectric nanoantennae for operation in the visible wavelength region; beam deflectors can serve as building blocks for other more complicated devices like metalenses. Compared to previous reports using local optimization approaches our approach improves device eciency; transmission eciency is especially improved for wide deflection angle beam deflectors. The ABC method with memetic search phase is also an improvement over the more commonly used GA as it reaches similar eciency levels with a 35% reduction in computation time. The method described here is of interest for the rapid design of a wide variety of electromagnetic metasurfaces irrespective of their operational wavelength.

Two opposite uni-directional radiation bands with good circular polarization (CP) characteristics are achieved in an Archimedean Spiral Antenna (ASA). A sandwich configuration is formed by utilizing two resonance based reflectors (RBRs) at the bottom and top sides of the ASA. Owing to the resonance characteristic, the RBRs do not act as reflectors at the other operational band, then, opposite uni-directional radiations are obtained, and the two uni-directional bands can be tuned independently. The proposed ASA with two uni-directional bands (ASA-TUB) has a wide impedance bandwidth about 4.4:1 (1.8-8 GHz), while its front-fire band (FFB) ranges from 1.8 GHz to 2.2 GHz (20.0%), and its back-fire band (BFB) is 4.4-7.1 GHz (46.9%) for front-to-back ratio (FBR) larger than 5 dB. The maximal FBRs for the FFB and BFB are 11.3 dB and 20 dB, respectively. Moreover, good CP performances are also obtained for the FFB and BFB. Besides, the whole profile of the proposed antenna is only 0.16 λ at the lowest operational frequency. The proposed antenna has the properties of dual opposite uni-directional radiation bands, low profile, good FBR and CP.

A compact stacked Yagi antenna is proposed with bandwidth enhancement in this paper. To reduce the size of the antenna and simultaneously improve the front-to-back ratio (FTBR), a reflector, modified with six slots, two λ0/4 meanderline-shaped slots and four straight short slots, is employed. Furthermore, a ladder-like director is designed to overcome the mismatch loss caused by the diminution of the height between the reflector and driven dipole. As shown in both simulation and measurement, the proposed compact Yagi antenna can achieve a compact size of 0.55λ0×0.55λ0×0.08λ0, |S11| ≤ -10 dB bandwidth of 17.2% and an FTBR of 22dB at 2.2GHz. The acceptable results make the proposed Yagi antenna a good candidate for applications where compact size and wide bandwidth are needed.

In this paper, the direction of arrival (DOA) and polarization parameters are estimated by a uniform circular array (UCA) with several single-polarized sensors. An ecient and improved polarization MUSIC algorithm for estimating the DOA and polarization parameters is presented. This method uses information on the amplitude to reduce the computational complexity. When the source is linearly polarized, the proposed algorithm is more accurate at a low signal-to-noise ratio (SNR). Monte Carlo simulations verify the ecacy of the proposed method.

To enhance the gain of conventional Vivaldi antenna (CVA), a novel dielectric sheets-covered Vivaldi antenna (DSCVA) is proposed. The dielectric sheets suck energy from the tapered slot region and flare termination region of the CVA, and thus act as surface wave antennas to improve end-fire performances. The CVA, DSCVA as well as the DSCVA with elongated tapered profile (SP-DSCVA) are designed, fabricated and measured. The simulation results are in good agreement with the experimental data. Measurement results show that the gain increase of the DSCVA is up to 5.1 dBi in the range of 3.5-16.5 GHz without increasing antenna length compared to the CVA. More gain enhancement is achieved for the SP-DSCVA. In addition, the half power beamwidths of the CVA as well as the sidelobe levels are improved in both E- and H-planes.

In this paper, a hybrid algorithm of binary lightning search algorithm and simulated annealing (BLSA-SA) is proposed to optimize the design of multilayer microwave absorbers for normal incidence. The multilayer absorber is designed to find a set of coatings that minimize the reflection coefficient over the desired frequency. The design problem is translated into solving the binary problem. Three different design examples are presented to verify the performance of the BLSA-SA. The results show that the reflection coefficient and thickness of BLSA-SA are better than those of other heuristic algorithms for multilayer absorber design. In the five-layer design, the standard deviation of BLSA-SA is the smallest among the 20 independent test results of the algorithms, which indicates that the BLSA-SA algorithm, has a strong stability.

This paper presents a Quad-Rectangular Shaped Microstrip Antenna (QRSMA) fed by a single microstrip line feed. QRSMA having different frequency bands is designed to be applied to L(1-2GHz), S(2-4GHz) and C(4-8GHz) bands applications. QRSMA is loaded with a single square patch and 4 rectangular patches. The patches are loaded using a flame retardant substrate (Fr-4). The patches are connected with 1 mm width of copper (Cu) stripline. Thus the proposed design of patches and width is responsible for desired multiband operations. The antenna resonates at frequencies f1=1.074, f2=3.119, f3=4.089, f4=5.683 and f5=6.514 GHz. Thus, the antenna is useful in the L, S and C band applications. Compared to other antenna designs, the proposed antenna exhibits multiband performance, size reduction and is economical. It also realizes tunability of frequencies having stable radiation pattern with compact electrical size. The paper analyses the simulated and experimental results. Various cases of QRSMA performances are also compared in this paper.

In this study, the misalignment of bistatic clutter spectral centers is considered, and an efficient adaptive main-lobe clutter compensation approach is presented for mitigating the bistatic geometry-induced clutter dispersion. In order to reduce computational load, an improved orthogonal matching pursuit (OMP) is introduced into the space-time clutter spectrum estimation. This method can accurately extract the required parameters for compensating the clutter spectral centers misalignment via sparse reconstruction with the desired Doppler cells. Simulation results are presented to demonstrate the effectiveness and efficiency of the proposed method.

In this paper, an asymmetric thrust magnetic bearing (MB) design principle and method are introduced. Different from the general design method of magnetic bearing, the asymmetric magnetic bearing design method focuses on the effect of asymmetric factor. A permanent magnet biased asymmetric hybrid thrust magnetic bearing (AHTMB) with secondary air-gap is designed in detail. A multi-objective optimization is conducted with genetic algorithm (GA) to get smaller mass and less loss. According to optimized model parameters, magnetic field distribution, stiffness and effect of asymmetry factor on stiffness are also analyzed. For stability of the system, equivalent stiffness and equivalent damping and current characteristics are deduced. Based on the analysis results and design methods, appropriate asymmetry factor asymmetric can be chosen to satisfy the different bias force requirement. With small number of coils and current, AHTMB with secondary air-gap is beneficial for decreasing the copper loss and enhancing dynamic performance of control system.

A subject of plasmonic spinphotonics is developed for surface plasmon polaritons (SPPs). Since an electromagnetic field is a vectorial field, it has spinning angular momentum, and thus spin current is one of its degrees of freedom. A spin current density tensor has 24 independent components because of its antisymmetry in coordinate indices. By using the law of conservation of electromagnetic angular momentum (i.e., orbital angular momentum plus spinning angular momentum), the electromagnetic spin current density tensor is derived, and its characteristics are indicated. Since surface plasmon polaritons can exhibit various intriguing optical and electromagnetic effects and have many practical applications, we consider a new potential effect relevant to spin current transfer. The electromagnetic spin current density tensor and its intensity profile are analyzed for SPPs sustained on a metal-dielectric interface. The plasmonic spin on a metal ring and a straight thin metal belt is calculated, and based on this, a nanomechanical effect caused by plasmonic spin current transfer is suggested. It is expected that such a nontrivial nanomechanical effect will be useful in the design of new nanophotonic devices aiming at sensitive, accurate measurement techniques.

A compact Ku-band bandpass filter (BPF) with wide pass-band, compact size and high selectively is presented. The presented BPF is composed of two quarter-wavelength resonators and a dual-mode resonator, resulting in a compact circuit size. The transmission zeros (TZs) located at the lower and upper stopband are achieved by the mixed electromagnetic (EM) coupling and dual-mode resonator, respectively, resulting in a high frequency selectively. The measured results show minimum in-band insertion loss, fractional bandwidth and variation of group delay to be 0.9 dB, 36.2% and 0.12 ns, respectively. Also, the stopband suppression is greater than 28 dB from 5 to 10.3 GHz and 30 dB from 19.5 to 29.5 GHz. The effective circuit size of the filter is 8.43×2.28 mm² (0.63 λg ×0.17 λg, where λg is the guide wavelength of 15.1 GHz.)

The configuration of an infinite planar conductive shield is examined when it is excited by an electromagnetic near field generated by a coil current source as that of a wireless power transfer (WPT) system. The analytical expressions of the electromagnetic field based on the transmission theory of shielding are given for different frequencies and different incidence angles of the near field generated by the coil current, assuming the conductive planar shield placed in the close proximity of the coil. The obtained results are discussed and compared with other traditional analytical and numerical solutions.

Based on convoluted interwoven element, a miniaturized frequency selective surface (FSS) with stable band-stop response is proposed in the paper. By extending the four dipoles into the adjacent elements, the equivalent inductance and capacitance are increased, and therefore the proposed FSS realizes promising miniaturization characteristics. The simulation results indicate that the resonant frequency is 1.19GHz, and the dimension is only 0.027λ0. Compared to traditional crossed elements, the size is reduced by 94.6%. Besides, the FSS has excellent angle-stability under both TE and TM waves. Finally, the proposed FSS is fabricated and measured, and the experiment results prove the satisfactory consistency with the simulation results.

This paper presents our research work on designing a dual-band dual-polarized (DBDP) series-fed S/X-band shared aperture antenna (SAA) for synthetic aperture radar (SAR) applications. The proposed SAA DBDP X-band antenna is designed with the concept of series-fed 4-group 2x2 planar arrays with high impedance microstrip line feeding in both vertical and horizontal polarizations. By etching out the inner edge elements from 2x2 X-band subarrays in all the four-groups, the S-band element could be accommodated. The design evolution stages have been presented. The S-band (3.2GHz) is best suited for volumetric soil moisture estimation using SAR and X-band (9.3 GHz) best suited for surveillance SAR applications and grain size estimation. To verify the antenna design concept, a prototype is fabricated and measured with both S-parameters and radiation characteristics including gain measurements. The antenna with reflection coefficient lS11l < -10 dB has an impedance bandwidth 3.12-3.42 GHz (9.3% BW) in S-band and 9.2-9.36 GHz (1.72% BW) in X-band. The measured isolation lS21l between two different bands in the same polarization is better than 25 dB, and the isolation between two different bands in two orthogonal ports is better than 30 dB. Measured gain of the antenna at S-band is better than 8.5 dBi at V-port and H-port, and X-band is better than 11 dBi at either port. Measured side-lobe level (SLL) at S-band is better than -17 dB at either port, and X-band is better than -20 dB at either port. The overall size of the S/X-DBDP SAA is 100 x 100 x 1.6 mm³. Measured results of the S/X-DBDP SAA show good agreement with the finite integration technique (FIT) based computer simulation technology (CST) microwave studio.

The power flow for electromagnetic wave absorbers consisting of pattern conductor layers acting as frequency selective surfaces, absorption layers, and short circuit layers was investigated by Poynting vectors. A method was developed to evaluate the flow of electromagnetic wave power by an electromagnetic wave absorber upon irradiation with electromagnetic waves. The results indicate that the electromagnetic wave absorption phenomenon involves generation of true power, a real part of the time averaged Poynting vector, which moves horizontally along the pattern surface after the incident wave has irradiated the pattern conductor from the vertical direction, and the direction of power flow changes to enter the polymer layer from the pattern interval, causing an accumulation of power inside the polymer layer, followed by absorption, which is converted into heat due to the loss factor.

Phantoms provide valuable test platforms for developing medical devices. Solid materials in particular allow fabrication of stable and robust models. This paper presents a novel, anatomically realistic, multi-layered head phantom made from dielectrically accurate, stable, easily mouldable, low-cost tissue-mimicking materials for testing of microwave diagnostic systems. Also incorporated is a mechanism for inserting reconfigurable lesions and a novel circulatory system modelling physiology. Tissue-mimicking materials composed of graphite, carbon black, and polyurethane with small volumes of acetone or isopropanol were fabricated and dielectric properties were measured across the 1 - 8.5 GHz band. The tissuemimicking material properties were adjusted until their dielectric properties matched those of reference values for target tissues of interest, thereby emulating: weighted aggregates of head tissues external to the brain, tissues comprising the brain, and blood. 3D printed anatomically realistic head and brain moulds cast the phantom mixtures for each layer. Cylindrical holes in the brain layer allow insertion of pathological lesion phantoms, such as haemorrhages. Tubing embedded in the brain layer forms a symmetrical loop providing a novel simplistic model of circulation. The resulting head phantom is anatomically realistic, dielectrically stable, enables pathology modelling, and has, uniquely, a circulatory loop. This novel head phantom provides a valuable test platform for microwave diagnostic studies.

In this paper, off-grid DOA estimation based on sparse representation and Rife algorithm is presented to improve performance when the sparse signal directions are not on the predefined angular grids. The algorithm is divided into two steps. Firstly, the real-valued sparse representation of array covariance vector (RV-SRACV) algorithm is used to do off-grid DOA estimation, and it does not need to estimate the noise power. Secondly, Rife algorithm is used to correct the DOA estimation, and after that the DOA can be accurately estimated. The effectiveness and superior performance of the proposed algorithm are demonstrated in the simulation results.