Currently, most full-polarimetric synthetic aperture radar (SAR) systems adopt linear polarization (LP). On the other hand, circular polarization (CP) is also becoming popular due to its various benefits over LP. However, since CP-SAR is an emerging technique, there are not many imaging and polarimetric analysis results in the literature. As a fundamental study on CP-SAR, this paper presents the results of an investigation on the CP properties of ground-based SAR (GB-SAR) echoes from various canonical targets and a rice paddy sample. The C-band data acquired in a laboratory environment are analyzed and interpreted by means of several factors such as calibration performance, experimental verification of theoretical scattering matrices, imaging quality and accuracy of scattering decomposition results. The eigenvector-based decomposition of the coherency matrix is adopted, and the performance of CP in retrieving the targets' dominant scattering mechanisms and physical parameters is evaluated from entropy-alpha (H-α) plane and orientation angle (β) value. Results demonstrate the effectiveness of CP in interpreting and discriminating the SAR image features mainly owing to its distinct advantage of highly reliable received signal strength.

This paper presents a frequency reconfigurable dual-pole, dual-band waveguide bandpass filter. Varactor diode and chip capacitor loaded planar split ring resonators are used on the transverse plane of a waveguide to form the filter. Numerical simulations are carried out using CST microwave studio (version 14). Measured result shows tuning range of the bands are 8.12-8.58 GHz and 10.22-10.68 GHz, respectively. The measured result shows good agreement with the simulated one. The total length of the proposed filter is 10 mm.

Multiple-input and multiple-output (MIMO) is currently regarded as a key technology for long term evolution (LTE), but a critical effect is mutual coupling (S₂₁) due to space constraint in miniaturized design. A compact-size antenna with low mutual coupling will be an ideal choice for better system performance. This paper describes the design of a small-size (48 × 48 mm²) MIMO antenna system with low mutual coupling for LTE 800 MHz applications. The antenna system comprises two FR-4 substrate layers; one printed with two meander line antennas (MLAs) and the other printed with reactive impedance surface (RIS) and defected ground structure (DGS). The properties of the antenna, such as S-Parameters, excited surface current distribution, far-field radiation pattern and diversity performance characteristics, were studied. The results indicated that MLAs rendered compactness to the system. Introduction of air gap (AG) between the two substrates, DGS and periodic square patches of RIS resulted in 452 MHz bandwidth and mutual coupling of -41.18 dB between antenna elements. The performance of the proposed design compared with other reported geometry has been demonstrated. Parameters including bandwidth, ratio of antenna area/improvement in S₂₁, antenna efficiency and the envelope correlation coefficient were compared. Considering the results, the present system appears to be comparatively more efficient.

This paper presents an electrical tunable bandpass filter based on tunable LC resonators loaded with semiconductor varactors. Magnetic dominated mixed coupling between the tunable resonators is utilized to compensate the bandwidth of the tunable filter. Cross coupling is created by using magnetic dominated mixed coupling between the resonators and source to load electrical coupling, and two transmission zeros are generated beside the pass band. The tunable mechanism of the proposed filter is studied. The tunable filter is analyzed, designed, fabricated and measured. The measurement shows that the filter can be tuned from 70 MHz to 270 MHz with a fractional bandwidth from 27% to 21%.

A single-feed circularly polarized wide-beam antenna is proposed for Compass Navigation Satellite System (CNSS) application. The antenna consists of four stepped arc-shaped arms, which are applied to generate circularly polarized radiation. To broaden the beamwidth, each arm is split up into two horizontal arc-shaped parts and one vertical part. The proposed antenna is simulated, fabricated and tested. The measured results show that the 10-dB return loss band of the proposed antenna is from 2.37 GHz to 2.65 GHz and the 3-dB axial ratio band from 2.42 GHz to 2.55 GHz, covering the receiving band (2.49175 GHz ± 4.08 MHz) of CNSS. Its 3-dB AR beamwidth is 181° at 2.491 GHz. For the horizontal radiation pattern of the proposed antenna at 5° elevation angle, the RHCP gain is greater than -1.1 dBic, and the out-of-roundness is 1 dB. Additionally, the proposed antenna has a size of 0.37λ₀×0.37λ₀×0.11λ₀ with respect to 2.491 GHz.

Interfering electromagnetic energy could be a very powerful pulse which is generated and incident onto communication system such as linear wire antenna through direct radiation. In this paper, the transient responses of the linear wire antenna such as dipole antenna under the impact of the early-time (E1) high-altitude electromagnetic pulse (HEMP) are investigated using the equivalent circuit due to a primary element used in the modeling of systems for HEMP vulnerability is the linear wire antenna such as dipole antenna. Based on the equivalence concept of HEMP radiation source and linear wire antennas, the response at receiving antenna port is calculated efficiently with an uncomplicated circuit composed of pulse voltage source and lumped elements. Numerical results are presented to confirm the accuracy of the proposed method.

A novel field-line-circuit hybrid algorithm based on finite difference time domain (FDTD) method is devoted to predicting the electromagnetic responses of transmission line with multi-ports network in a shelter in this paper. The full wave FDTD method, transmission line FDTD method, and the modified nodal analysis (MNA) are combined to be compatible with the multi-level electromagnetic (EM) coupling progress of the electromagnetic interference (EMI) problem. The proposed method divides the EM couplings among the spatial EM fields, antennas, transmission line networks, and terminal circuits in some typical electronic systems into different levels with appreciate simulation techniques used. The accuracy of the hybrid method is verified by comparing the terminal transient voltage responses of transmission lines with the results obtained by PSPICE, and good agreements are achieved. Numerical calculations are further performed to show the terminal coupling voltages and currents, and the effects of incident directions and polarizations of the illuminated electromagnetic pulse (EMP) are both taken into account.

An octagonal shape monopole antenna with dual band-notched features used for ultra-wide band applications is presented. The monopole antenna has good impedance matching from 3.4 GHz to 12 GHz. The dual notched bands are achieved by using a U-shaped parasitic strip and meandered slot etched in the radiating patch. The first band notched is achieved using meandered slot to reduce the interference with WIMAX from 3.3 GHz to 3.9 GHz. The second band notched is achieved using U-shaped parasitic strip which is placed above the ground plane to eliminate the interference with WLAN from 5.2 GHz to 5.9 GHz. The proposed antenna is designed, simulated and measured. The measured result show that the antenna structure achieves (VSWR < 2) from 3.2 to 10.8 GHz. Also, the simulated radiation pattern and current distribution at different frequencies are presented. The measured and simulated results confirm that the proposed antenna is suitable for UWB applications.

In this paper, a measurement procedure allowing the characterization of active integrated antennas in terms of intermodulation distortion and compression point inside of a parallel plate cell is presented. The validity of the radiative measurement is shown and compared to the traditional guided procedure. A good agreement between the two methods shows that this approach allows the evaluation of the overall linearity behavior of arbitrary complex integrated antennas and can serve as a complementary tool when the traditional guided method cannot be applied.

In underwater wireless optical communication links, the suspended particles in the water can lead to multi-path transmission of the light, causing the temporal dispersion and attenuation of beam pulse. The scattering phase function is a key parameter to model angle scattering in the Monte Carlo simulation and can be approximated by the commonly used Henyey-Greenstein (HG) phase function, but in turbid sea water environment, the HG phase function cannot match well with the measured value of the particle phase function. In this work, instead of using the HG phase function, we make use of the Petzold's measured data value of the scattering phase function in turbid sea water. We propose a numerical solution for the computing of the scattering angle based on the measured particle phase function and present the difference of effect on temporal dispersion between the measurement and HG phase function. Numerical results show that our model is more accurate than the widely used HG model. An analytic double Gamma function is used to fit the Monte Carlo simulation results, and a good fit is found between the double Gamma function and the Monte Carlo simulations.

A regularization is integrated with Forward-Backward Time-Stepping (FBTS) method which is formulated in time-domain utilizing Finite-Difference Time-Domain (FDTD) method to solve the nonlinear and ill-posed problem arisen in the microwave inverse scattering problem. FBTS method based on a Polak-Ribiète-Polyak conjugate gradient method is easily trapped in the local minima. Thus, we extend our work with the integration of edge-preserving regularization technique due to its ability to smooth and preserve the edges containing important information for reconstructing the dielectric profiles of the targeted object. In this paper, we propose a deterministic relaxation with Mean Square Error algorithm known as DrMSE in FBTS and integrate it with the automated edge-preserving regularization technique. Numerical simulations are carried out and prove that the reconstructed results are more accurate by calculating the edge-preserving parameter automatically.

In this paper, a compact triple-band bandpass filter based on composite right/left handed (CRLH) approach has been proposed. The zeroth order resonance (ZOR) frequency of the designed filter can be controlled effectively by varying the series parameters. A new circular interdigital capacitor is integrated to provide series capacitance. The number of passbands depends on number of rings of circular interdigital capacitor (C-IDC). In order to validate metamaterial behavior, a dispersion diagram has been plotted for the designed filter. The proposed filter offers measured 3dB fractional bandwidth of 71% at 1.7 GHz, 24% at 2.9 GHz and 12% at 4.1 GHz as center frequencies. The designed filter will be suitable for different wireless applications such as global navigation satellite systems (1.559-1.610 GHz), GSM1800, indoor femtocells (2.5-2.7 GHz), air traffic surveillance (2.7-2.9 GHz) and fixed satellite services (3.8-4.2 GHz). The size of the proposed filter is 0.13λ0 × 0.11λ0, where λ0 is the free space wavelength at ZOR frequency of 1.7 GHz.

In this letter, a compact ultra-wideband (UWB) bandpass filter based on CPW-to-microstrip transition structure is proposed. Compared with traditional UWB BPF using hybrid structures, the proposed filter has a more sharp selectivity due to a transmission zero located at the lower edge of the passband generated by the combined effect of both CPW-MS-CPW and interdigital coupling line (ICL). Moreover, to further improve its selectivity, the CPW open stubs (CPWOS) are introduced to produce two extra transmission zeros at high frequency. The measured results show that the proposed filter has some good characteristics such as sharp roll-off, compact size (0.54λg × 0.38λg) and a very wide fractional bandwidth of 130%, which is a significant improvement to what has been reported for UWB BPF with similar structures.

A nonlinear hybrid FDTD/FETD technique based on the parametric quadratic programming method is developed for Maxwell's equations with nonlinear media. The proposed technique allows nonconforming meshes between nonlinear FETD and linear FDTD subdomains. The coarse structured cells of FDTD are used in relatively simple structures with linear media, whereas fine unstructured elements of FETD based on the parametric quadratic programming method are used to simulate complicated structures with nonlinear media. This hybrid technique is particularly suitable for structures with small nonlinear regions in an otherwise linear medium. Numerical results demonstrate the validity of the proposed method.

A compact dual band-notched ultra-wideband (UWB) multiple-input multiple-output (MIMO) antenna with uniform rejection performance is designed on an FR4 substrate (35×23×1.6 mm³). Compared with the existing UWB MIMO antennas, a second-order notched band with uniform performance for 5.15-5.825 GHz is achieved, which results from the interplay between a 1/3λ open-end slot and a 1/2λ parasitic strip. A 1/4λ open-end slot is also applied to the 3.3-3.7 GHz reject band. The two slots are connected at their open ends, that can help to get the uniform reject performance for 5.15-5.825 GHz and make the high cutoff frequency of the impedance matching band go toward the higher frequencies. Excluding the two rejected bands, a band with |S₁₁|≤-10 dB, |S₂₁|≤-17 dB and frequency ranged from 3.1 to 10.9 GHz is achieved, and results show that a uniform performance for 5.15-5.825 GHz is obtained.

In this paper, a novel design for a wideband integrated photovoltaic (PV) solar cell patch antenna for 5 GHz Wi-Fi communication is presented and discussed. The design consists of a slot loaded patch antenna with an array of complimentary split ring resonators (cSRR) etched in the ground plane. This is then integrated with a solar cell element placed above the patch, where the ground plane of the solar cell acts as a stacked antenna element from an RF perspective. The design is simulated on CST Microwave Studio and fabricated. The results indicate that an impedance bandwidth of 1 GHz is achieved to cover the 5 GHz Wi-Fi band with a gain of between 7.73 dBi and 8.18 dBi across this band. It is also demonstrated that size reduction of up to 25% can be achieved. Moreover, it is noted that using a metamaterial loaded ground plane acts as an impedance transformer, therefore the antenna can be fed directly with a 50 Ω microstrip feed line, hence further reducing the overall size.

This paper represents the force calculation in a radial passive magnetic bearing using Monte Carlo technique with general division approach (s-MC). The expression of magnetic force is obtained using magnetic surface charge density method which incurs a multidimensional integration with complicated integrand. This integration is solved using Monte Carlo technique with 1-division (1-MC) and 2-division (2-MC) approaches with a MATLAB programming. Analysis using established methods such as finite element method (FEM), semi-analytical method, and adaptive Monte Carlo (AMC) method has been carried out to support the proposed technique. Laboratory experiment has been conducted to validate the proposed method. 2-MC gives better result than 1-MC. The computation time of the proposed method is compared with the quadrature method, FEM and AMC. It is observed that the proposed method invites less computational burden than those methods as the algorithm adaptively traverses the domain for promising parts of the domain only, and all the elementary regions are not considered with equal importance.

In this paper, an interdigital resonator that can greatly decrease mutual coupling between adjacent patches is proposed to realize an ultra-compact microstrip antenna array operating in 2.4 GHz wireless communication system. Due to its remarkable performance of decoupling, the edge to edge distance between adjacent patches can be reduced to 0.08λ₀ and even less. Meanwhile, a miniaturized feeding network, which is composed of a CRLH-TL-based phase shifter and T-junction-based power divider, is used to feedthe compact antenna array. The simulation results show that the proposed antenna array has an impedance bandwidth of 8.34%. We fabricate the antenna array to verify its performance. The experimental results are in good agreements with the simulations. Compared to the published designs, the proposed antenna array hasanultra-compact structure and hence can be used in space limited communication systems.

This paper presents a finite-difference time-domain (FDTD) method of the infinite half-space with nonuniform meshes, aiming to speed up the FDTD calculation of scattering of buried objects. Two 1-D modified FDTD equations are employed to set plane wave excitation of the infinite half-space scattering problems. In order to reduce calculation time and meshes, a method with nonuniform meshes is applied. Fine grids are used for the buried objects and underground while coarse grids are applied for other regions. The 1-D modified FDTD equations with nouniform meshes are derived, and the settings of total-field/scattering-field (TF-SF) boundary are given. Finally, the proposed method is applied to calculate the transient scattering field of a buried mine. Numerical results demonstrate the validity of the method and the simulation time is significantly reduced when compared with uniform meshes FDTD.

The interference behaviors of a vector optical field with both radially and azimuthally variant states of polarization (SoP) through the Young's two-slits are theoretically studied. The optical field distribution with periodic stripes in the far field results from the interference of the vector optical field through the Young's two-slits with different initial SoP distributions. It is found that the far-field distribution can be manipulated by the incident vector optical field with the initial phase and SoP distributions. Particularly, the distribution of radially-variant SoP in the cross-section of the incident optical field provides an additional freedom to control the interference patterns of the x-component, y-component and total intensity distribution in far field. This approach provides a new method to further expand the functionality of an optical system by considering the distribution of SoP in field cross-section.