An asymmetric stepped-impedance ring resonator (ASIRR) is proposed for the design of a triple-bandpass filter. This resonator is applied to creat the former two passbands by utilizing a stepped-impedance circular ring and the third passband by introducing two asymmetric coupling structures. It is found that the S-parameter performance can be improved by adding a pair of shorted and open stubs, the second passband and the stopbands on both sides of the third passband can be tuned by adjusting the length of open stubs. A prototype filter operating at 1.04, 3.52 and 5.57 GHz is designed, fabricated, and measured with the corresponding fractional bandwidths of 23.1%, 7.4%, and 4.1%. Good agreements between the simulated and measured results are achieved for the ASIRR filter. Also, four transmission zeros are generated.

Magnetic induction tomography has been under consideration for imaging electrical conductivity distributions within the human body. Multi-coil systems are most commonly employed for this task, requiring a numerical solution of Maxwell's equations at each position of the coil array. An alternative uses a single coil placed near the conductive target while measuring coil self-impedance changes (``coil loss'') at a number of unique locations. Recently, a closed-form solution of Maxwell's equations, in the form of a 3D convolution integral, was found for a single coil consisting of concentric circular loops that relates impedance change to an arbitrary conductivity. Its development required spatially uniform permittivity and permeability, yet showed quantitative agreement with experiment. Here, we provide a much more critical test of the convolution integral in experiments that allow large permittivity changes over coil dimensions. Loss is measured while the coil is placed at known positions relative to plastic columns of variable diameter which are filled with salt solutions of varying conductivity. In all cases, coil loss varies linearly with conductivity and with zero intercept. Quantitative agreement is observed only when column diameter is greater than or equal to coil diameter. Because of linearity, the convolution integral is useful for image reconstruction, though contrast could be either reduced or enhanced in those circumstances when relative permittivity change exceeds ~70.

Two techniques are described for the calibration of ground-based (GB) circularly polarized (CP) full polarimetric radars. The techniques are based on the point target calibration approach that uses various types of canonical reflectors with different orientations. Specifically, the calibration methods for linearly polarized (LP) radar proposed by Wiesbeck et al. and Gau et al. are selected and adapted to CP with suitable reflectors. The applicability of the techniques is examined through C-band scatterometric and synthetic aperture radar (SAR) measurements in an anechoic chamber. For the scatterometric mode, comparisons of calibrated channel imbalances with theoretical values show agreement within ±0.3 dB in amplitude and ±5˚ in phase. The crosstalk between the channels is also reduced by ~5 to 30 dB after calibration. For the SAR mode, calibrated scattering matrix of a vertical wire target exhibits significant elimination of distortions between channel amplitudes and phases. The effect of calibration on target parameter retrieval is also investigated through the Cloud-Pottier eigenvector-based decomposition. Both calibration techniques are shown to yield improved accuracy of entropy-alpha (H-α) distributions and orientation angle (β) values.

The diffraction by a finite parallel-plate waveguide with sinusoidal wall corrugation is analyzed for the E-polarized plane wave incidence using the Wiener-Hopf technique combined with the perturbation method. Assuming that the corrugation amplitude of the waveguide walls is small compared with the wavelength and expanding the boundary condition on the waveguide surface into the Taylor series, the problem is reduced to the diffraction by a flat, finite parallel-plate waveguide with a certain mixed boundary condition. Introducing the Fourier transform for the unknown scattered field and applying an approximate boundary condition together with a perturbation series expansion for the scattered field, the problem is formulated in terms of the zero-order and the first-order Wiener-Hopf equations. The Wiener-Hopf equations are solved via the factorization and decomposition procedure leading to the exact and asymptotic solutions. Taking the inverse Fourier transform and applying the saddle point method, a scattered far field expression is derived explicitly. Scattering characteristics of the waveguide are discussed in detail via numerical examples of the radar cross section (RCS).

In this paper we compare, using ISRO's RISAT-1 FRS-1 mode Compact Polarimetric (CL-Pol) data, two widely used hybrid polarimetric decomposition techniques, m-δ and m-χ decompositions, with regard to classification accuracy for various agricultural crops of north and west India. We show that the classification based on the m-χ decomposition results in better crop separability in general. But the crop stage and existence of orientating structures in the crops affects the efficacy of decomposition; a fact vividly brought out in this paper. Theoretical insights into the effectiveness of these decomposition techniques for different crop geometry are brought forth. We also compare the classification accuracy subsequent to polarimetric speckle filtering vis-a-vis spatial multilooking (downsampling). We show that usage of an appropriate polarimetric filter tends to produce comparable accuracy for most of the agricultural classes, as that of multilook case, without degrading spatial resolution. This work showcases a custom implementation of Stokes parameter based decomposition as well as POLSAR filter based on refined Lee algorithm, written in C and tailored to RISAT-1.

This paper presents a testing scheme for the steel corrosion in reinforced concrete based on near-field effect of meter wave. The physical mechanism of the near-field method was introduced, and the structure of the measurement device was presented in detail. The electromagnetic field near the steel bar buried in the concrete structure was simulated by the finite difference time domain method. The simulated data show that the mean radiation power decreases monotonously with the increase of the corroded depth of the steel bar, and the corroded area is promising to be imaged directly due to the localization of near field. The results indicate that the near-field technique can act as a new nondestructive testing technique to detect and even image the corrosion area buried in concrete in engineering structure.

In this paper, a feature fusion algorithm is proposed for automatic target recognition based on High Resolution Range Profiles (HRRP). The proposed algorithm employs Convolution Neural Network (CNN) to extract fused feature from the time-frequency features of HRRP automatically. The time-frequency features used include linear transform and bilinear transform. The coding of the CNN's largest output node is the target category, and the output is compared with a threshold to decide whether the target is classified to a pre-known class or an unknown class. Simulations by four different aircraft models show that the proposed feature fusion algorithm has higher target recognition performance than single features.

A compact microstrip resonator based on the interdigital structure is proposed. The resonator has several times higher unloaded quality factor compared to similar resonators presented previously and can even reach the Q-factor of a regular λ/4 resonator. The size of the resonator can be significantly reduced with a substantial increase in quality factor by incrementing the number of pins in the interdigital structure. In addition, for each gap between the pins exist an optimal number of pins that correspond to the maximum Q-factor. An extension of the upper stopband for a bandpass filter designed using the resonator can be achieved by the interconnection of the pins in each of the comb structures. The simulation results were proven by fabricated resonators and 4-pole bandpass filter. For the central frequency of 2000 MHz and 16.2% fractional bandwidth, the lateral size of the filter is only 11.5 mm×3.8 mm for alumina substrate (eps=9.8). The filter has an upper stopband up to 5.8f₀ at the level -40 dB.

In this paper, a new compact tri-band bandpass metamaterial (MTM) filter based on meander line with a rectangular stub is proposed and designed. The pseudo connections between meander line and ports generate interdigital capacitor (IDC) to provide series capacitance. Meander line a rectangular stub is plotted. The proposed filter offers measured first passbands from 1.88-4.0 GHz; second band starts from 5.4-5.9 GHz; third passband ranges from 7.1-7.4 GHz. It has insertion losses of 0.8 dB, 1.5 dB and 2.0 dB at 2.1GHz, 5.7 GHz and 7.3 GHz centre frequencies, respectively. The designed filter will cover S band (2-4 GHz), ISM band (5.725-5.875) and fixed satellite services (7.25-7.3 GHz). Further, the designed filter shows electrical size of 0.14λ₀ × 0.13λ₀ at zeroth order resonance (ZOR) frequency 2.1 GHz.

This paper proposes a compact E-Plane five-port waveguide power combining and splitting structure in the V-band. The symmetrical five-port structure guarantees excellent amplitude and phase consistency between the input/output ports. Two isolation ports guarantee high isolation between the input/output ports. Meanwhile, the E-plane waveguide structure is more compact than H-plane structure. A two-way power combing structure working from 59 GHz to 64 GHz is designed, fabricated and measured for validating our structure. The measured results show that the phase and amplitude differences between the input ports are smaller than ±1.0 degree and ±0.1 dB, isolation between the input ports higher than 18 dB, the insertion loss and return loss lower than 0.2 dB and better than 17 dB, respectively.

A low-profile wideband circularly polarized (CP) microstrip antenna with conical radiation pattern is designed in this paper. Based on the center-fed circular microstrip patch structure, the proposed antenna symmetrically employs 5 shorting vias connecting the patch and the ground plane to provide the θ-polarization and 11 slant sector branches at the edge of circular patch to generate the φ-polarization. With the phase difference of 90° between the two orthogonal polarizations, the design radiates right-handed circularly polarized (RHCP) waves. The proposed antenna works at three resonant modes. To realize broad operating bandwidth, the slant sector branches should be carefully adjusted to make the second resonant mode couple the first mode (TM₀₁ mode) and third mode (TM₀₂ mode) together. The measured results show that the proposed antenna has a low profile of 0.025λ, impedance bandwidth of 35.4% (3.74-5.35 GHz), and axial ratio (AR) bandwidth of 38% (3.7-5.45 GHz). To further verify the characteristics of the proposed antenna, the studies on several important parameters are carried out by HFSS simulation, and a simple design guideline is provided.

A magnetically suspended permanent-magnet motor (MSPMM) system mainly consists of magnetic bearings(MBs), a motor and a rotor assembly. This paper focuses on the system analysis of an MSPMM used for a vacuum turbo-molecular pump (TMP). To ensure a normal levitation and rotation, characteristics of electromagnetic field of MBs and motor are studied. For MSPMM, loss is the main heat source. To ensure the safe and steady operation of MSPMM, loss of the MB and motor are calculated and analyzed by finite element method (FEM). For thermal aspects, temperature field is estimated. Based on these analyses, the system performance can be predictive. Considering the poor heat dissipation conditions in a vacuum environment, this system analysis including loss and temperature field is of great value for MSPMM design.

A single-layer reflectarray antenna using circular patch with four semicircular ring slots is proposed in this paper. By changing the diameter of the circular patch, the proposed phasing element can realize phase range about 500 degrees with relatively stable reflection magnitude. Besides, the reflection phase curve with smooth slope is almost linear. Based on the good phase response, a 421-element reflectarray is designed, simulated and fabricated. The measured results show that 1.5-dB gain bandwidth can attain 24% at the center frequency of 15 GHz.

A new technique is developed to couple the advantages of both the microstrip patch antenna and rectangular waveguide. An equilateral triangle is used as a radiating patch. This patch is fabricated on one face of a single-layer dielectric substrate with double-sided copper clad coated with tin, and on the other face an iris is fabricated and coupled to the waveguide. Antenna parameters such as return loss and bandwidth are studied for a circular patch. The results obtained are discussed in detail and explained. Matlab PDE toolbox is used to generate two-dimensional meshes. These meshes are converted into a three-dimensional form using subdomain numbers. RWG basis functions are used for MoM to calculate impedances. Reection coefcient and 2D current are obtained using the complex impedances.

A novel asymmetrical single-pole double-throw (SPDT) switch for 2.4 GHz application with high power handle ability is developed. The novel asymmetrical topology is discussed. To increase the power capacity, ac-floating and dc-bias techniques are used. Using these techniques, a switch achieves a measured P1 dB of 20.5 dBm, an insertion loss (IL) of 1.16 dB and isolation loss of 20.8 dB in TX mode; an insertion loss of 1.57 dB and an isolation of 21.6 dB in RX mode. The circuit is fabricated using 3.3-V 0.35-μm DNW NMOS transistors in 0.18-μm bulk CMOS process.

In this article, design and analysis of a compact wideband short-ended metamaterial antenna based on composite right and left handed transmission line (CRLH-TL) is presented. The proposed antenna is configured with two different shapes (Half ring and simple gap) of series gaps and short ended boundary condition. It offers wide bandwidth by placing two different shapes of series gaps in such a manner, so that the first resonance frequency, i.e., zeroth order resonance (ZOR), second resonance frequency and third resonance frequency occur near each other, and hence combination offers wide bandwidth. Because of the applied boundary conditions, resonant modes can be controlled by series parameters of the proposed antenna structure. Further, coplanar waveguide feeding technique is used which replaces the requirement of via and allows the fabrication of a single layer antenna prototype. The proposed antenna is modeled by using ANSYS HFSS 14.0, and simulated results are verified with experimental ones of the prototype. The simulated fractional bandwidth of the proposed antenna is 52.38% centered at 3.57 GHz. Furthermore, the proposed antenna provides an average broadside gain of 2.30 dBi with average radiation efficiency of 94.95% in the entire working band of antenna.

A new approach to design of a dual-band power divider with only one section transmission line is proposed. Apart from the isolation resistor, admittance matrix is used to synthesize the dual-band divider. According to the required admittance matrixes at two frequencies, a modified configuration with shunting open/short stubs at each port is presented. A new compact dual-band (operating at 1.0 GHz and 4.5 GHz) is developed to validate this proposal. Experimental results demonstrate that the return loss is better than -19.2 dB, insertion loss less than 0.59 dB, and isolation better than 23.61 dB at two operation frequencies. The measured relative bandwidths of 15 dB return loss are 35.9% and 12.4% for the lower and higher bands, respectively.

In most applications of antenna arrays, side lobe levels (SLLs) are commonly unwanted. Especially, the first side lobe level which determines maximum SLL is the main source of electromagnetic interference (EMI), and hence, it should be lowered. A procedure of finding the optimum side lobe-minimizing weights for an arbitrary linear equally spaced array is derived, which holds for any scan direction, beam width, and type of antenna element used. In this science article, the use of convolution procedure and the time scaling property reduces the side lobe level for any type of linear equally spaced array. Results show that by this procedure, the side lobe level is reduced about two times or even more.

The radiation characteristics of a cylindrical array antenna for Multifunction Phased Array Radar (MPAR) and Terminal MPAR (TMPAR) applications are presented. A probe-fed stacked microstrip patch antenna is used for array elements. In calculations, the embedded element pattern of the patch antenna is obtained by simulation of a 5×5 element planar array. The radiation pattern of the TMPAR- and MPAR-sized cylindrical array antenna is calculated using the coherent addition method which is veried with full-wave simulation. For cross-polarization suppression, the array elements are arranged with identical 2×2 element subarrays. The radiation patterns of MPAR and TMPAR cylindrical array antennas with and without image conguration are calculated and compared. It is shown that the low cross-polarization level and azimuthally scan invariant beam characteristics can be achieved by the cylindrical array with image arrangement.

A wideband circularly polarized (CP) cross-dipole antenna is proposed for wireless applications. In this design, four parasitic square patches are utilized around the radiation patch to enhance the Axial-ratio (AR) bandwidth. By employing the bowtie-shape dipoles, the proposed antenna can achieve a wide impedance bandwidth. Meanwhile, by integrating with a curved-delay line which provides a 90° phase difference, the proposed antenna can radiate a CP pattern. A prototype is calculated, fabricated, and measured. Good agreement between the simulated and measured results is achieved. The measured results show an impedance bandwidth for VSWR≤2 of 47.73% (1.93-3.14 GHz) and a 3-dB AR bandwidth of 42.8% (2.00-3.09 GHz).