An approximate self-consistent solution of the problem of plane electromagnetic wave diffraction on a thick grating of metallic bars with slits between the bars filled a Kerr-type nonlinear dielectric is solved. The bistable operating regime of wave transmission through the grating is studied.

In this paper, different causal sub-domain temporal basis functions are investigated to make the explicit marching-on-in time schemes converge and stable for solving two dimensional time domain EFIE. PEC cylinders with arbitrary cross section are illuminated by a TE-polarized Gaussian plane wave. Two different approximations are used for calculation of the singular elements of the impedance matrix analytically. In the Time Domain Method of Moment (TD-MoM) formulation of the Electric Field Integral Equation (EFIE) of the problem, the free-space two-dimensional Green's function and triangular spatial basis function are used. By employing Galerkin's method in spatial domain and point matching in time domain, all time convolution integrals and self-terms are evaluated analytically to increase the accuracy and stability of the proposed technique. The stability and efficiency of the new technique are confirmed by comparison with literature.

In cloaking, a body is hidden from detection by surrounding it by a coating consisting of an unusual anisotropic nonhomogeneous material. The permittivity and permeability of such a cloak are determined by the coordinate transformation of compressing a hidden 2D or cylindrical body into a line. Some components of the electrical parameters of the cloaking material (ε, μ) are required to have infinite or zero value at the boundary of the hidden object. In order to eliminate the zero or infinite values of the electrical parameters, approximate cloaking can be used by transforming the cylindrical body virtually into a small cylinder rather than a line, but this produces some scattering. The solution is obtained by rigorously solving Maxwell equations using angular harmonics expansion. In this work, the scattering pattern, and the backscattering cross section against the frequency for cloaked conducting and dielectric cylinders are studied for both transverse magnetic (TM_z) and transverse electric (TE_z) polarizations of the incident plane wave for different transformed body radii.

In inverse synthetic aperture radar (ISAR) imaging, micro-motion structures on the target will induce additional time-varying frequency modulations to the radar echoes. Due to the disturbance of these mechanical vibration or rotation parts in the ISAR imaging, it will be difficult to obtain a well-focused ISAR image of the target using conventional translational motion compensation methods. To solve this problem, two improved translational motion compensation techniques have been proposed in this paper. Firstly, the power transform is used in the range bin aligment processing to depress the disturbance of the micro-motion parts. Then, a impreoved autofocusing methods based on range bins selection is presented, which only use the range bins of the radar returns of the main body scatterers for the phase adjustment. The results from the measured data are given to verify the validity of the improved translational motion compensation techniques proposed in this paper.

The quest to understand the variation of rainfall microstructures at subtropical and equatorial regions is vital to rain attenuation studies. In this study, point rainfall datasets obtained at Butare (2°36'S, 29°44'E) and Durban (29°52'S, 30°58'E), are compared at the reflectivity threshold of 38 dBz. Joss- Walvogel (JW) distrometer measurements collected from these two locations represent physical rainfall data from equatorial and subtropical climates respectively. The reflectivity threshold enables the classification of rainfall datasets into stratiform and convective (S-C) precipitation regimes. These thresholds, Rth, at Durban and Butare are analysed based on three known rainfall microphysical parameters: rain rate, rainfall Drop Size Distribution (DSD) and radar reflectivity. The results from rain rate distributions at the both regions are similar for both stratiform and convective classes. However, the sampled DSDs indicate the dominance of larger rain droplets at Butare compared to observations at Durban, irrespective of the rain classes. In addition, it is found that the reflectivity distributions at both regions, under stratiform and convective conditions, are distinct in their probability profiles. The overall S-C analysis implied that the structures of the reflectivity and DSD profiles at both regions - result in significant variation of predicted specific attenuation - at microwave and millimeter band. In comparison with other global locations, it is affirmed that the S-C transition occurs globally at rain rates between 6 mm/h and 13 mm/h.

The Doppler phenomena caused by a moving receiver or environmental scatters around a receiver are emulated in an AC(Anechoic Chamber) and a RC(Reverberation Chamber) using platform and mode stirring. In order to verify the emulated Doppler spread spectrum, the measured results in the AC and the RC have been investigated to incorporate Jakes's and 802.11 TGn Doppler models, respectively.

A simple and analytical design methodology for a novel planar four-port structure to implement power divider (PD) or balun with variable power division is proposed in this paper. It consists of two different 3 dB branch-line couplers and one coupled-line phase shifter whose length can be changed to implement variable power division. Different from the previous designs, the power divider and balun with variable power division can be realized in only one circuit by changing the electrical length θ₀ of the coupled line when the impedance ratio g is selected. According to the ABCD parameters and linear algebra calculation, closed-form mathematical equations for the circuit electrical values and scattering parameters can be obtained. A prototype with this proposed circuit, operating at 2 GHz, has been designed and fabricated using microstrip technology. Good agreements between the calculated and measured results verify our design.

Among ship detection methods for SAR image, constant false alarm rate (CFAR) is the most important one. However, several factors, such as detector parameter and distribution of ocean clutter, affect the performance of CFAR detection. This paper proposes a novel hierarchical complete and operational ship detection approach based on detector parameter estimation and clutter pixel replacement, which is considered a sequential coarse-to-fine elimination process of false alarms. First, a simple barycentric algorithm is adopted to estimate target-window size, and a morphology method is used to estimate false alarm rate for CFAR detector. Second, a clutter pixel replacement approach based on the statistical features of sea clutter is presented to obtain statistically independent, stationary, and Weibull distributed random data for CFAR detector to remove all false alarms. Experimental results of the detection methods on a SAR image dataset show that the proposed approach is effective in reducing false alarms and obtains a satisfactory ship detection performance.

An ultra-thin triple-band metamaterial absorber (MA) is proposed in the microwave region, which is composed of a periodic array of three rotated square rings (RSRs) and a continuous metal film separated by only 1 mm dielectric substrate. The fabricated MA exhibits three experimental absorption peaks at 4.88 GHz, 7.88 GHz, and 11.32 GHz with the corresponding absorption rates of 98.8%, 96.5%, and 95.9%, which shows an excellent agreement with the simulated results. The triple-band MA is polarization-insensitive at the normal incidence. Finally, the multi-reflection interference theory is introduced to interpretate the absorption mechanism. The calculated absorption rates of the improved unit cell for the strongly coupled MA coincide well with the simulated results at wide angles of incidence for both transverse electric (TE) and transverse magnetic (TM) waves.

This paper presents three dielectric resonator (DR) unit elements loaded with one, two, and three narrow slots underneath for designing reflectarrays. The slots are aligned in parallel, and the lengths are varied to function as phase shifter for changing reflection phase. It is found that the dominant TE mode of the square DR element can be easily excited by placing multiple parallel slots beneath a DR element. Study shows that the number and width of the slots can be used as additional design parameters for tuning the reflection loss and phase range of the reflectarray. Rectangular waveguide method has been deployed, showing reasonable agreement between simulation and measurement. It is found that a reasonable reflection phase range of 313° with slow slope is obtainable when the DRA is loaded with two slots beneath, which can be used for designing a small-size reflectarray. The reflection characteristics of the unit elements are studied, along with a complete parametric analysis.

Barrage and deceptive jamming can mask the synthetic aperture radar (SAR) signals and render SAR useless. In this paper, a novel jamming suppression method based on plolarization SAR (PolSAR) is proposed. After range compression, the barrage jamming has a noise-like characteristic while the real echo and deceptive jamming are focused. According to this, the barrage jamming is removed via a minimum entropy algorithm. Based on the different polarization characteristics between deceptive jamming and the real echo, the deceptive jamming can be suppressed by phase compensation in doppler domain. Simulation results are shown to demonstrate the validity of the proposed method.

The adaptive cross approximation is applied to boundary element matrices coming from 2D scattering problems by an infinite periodic surface. This compression technique has the advantage to be applied before the assembly of the matrix. As a result, the computational times for both assembly and solution phases are reduced. Numerical results assess the efficacy of the method on scattering problems with several periodic surfaces.

This paper mathematically models the operation of Arrayed Waveguide Grating (AWG) based multiplexer (MUX) and demultiplexer (DEMUX) used in optical networks. In WDM networks, the optical MUX and DEMUX play a crucial role of managing the aggregation and segregation of wavelengths for networking applications. A simple and intuitive model of AWG based MUX design is discussed in this work. This model assumes that the device is linear, in which the principle of superposition is valid, and the primary emphasis is given to the optical power gain of the individual wavelengths. By using this model, one can exactly estimate the individual and overall power associated with each of the multiplexed wavelengths. The developed model was evaluated with experimental results using AWG based multiplexers. The experiments were repeated for different test cases with various power input levels and multiplexer configurations. It was found that the developed model provided a good approximation to the actual AWG mux/demux.

A new design for a compact and wideband circularly-polarized rectenna with high efficiency operating at X-band is proposed. A dual-slot coupled antenna excited by an H-shaped slot fed by a T-shaped microstrip is designed to yield wideband performance as a receiving array antenna. Rectifying circuit models for harmonic suppression circuit, impedance matching, DC-pass circuit, and DC return circuit at the input and output of the diode are built up and optimized to transfer the maximum power from the antenna to the load using an ADS circuit simulator. An RF-DC conversion efficiency of 71.9% is measured on the conditions of 300 load, and 50.1 mW RF input power at 9.5 GHz operating frequency. For the proposed wideband rectenna, the efficiency of more than 50% is measured over a 1 GHz frequency bandwidth. The measured gain, axial ratio, and return loss of the circularly polarized antenna with a 4-element array are 11.2 dBi, 1.1 dB, and -16.4 dB, respectively. The reflection coefficient of the array antenna is measured at less than -10 dB over a wide frequency range of about 2 GHz. Using this antenna as transmitting (TX) and receiving (RX) radiators, the free-space power transfer capability of the rectenna is tested in free space to turn on an LED at 25 cm distance.

In this paper, the feasibility of Substrate Integrated Waveguide (SIW) couplers, fabricated using single-layer TACONIC RF-35 dielectric substrate is investigated. The couplers have been produced employing a standard PCB process. The choice of the TACONIC RF-35 substrate as alternative to other conventional materials is motivated by its lower cost and high dielectric constant, allowing the reduction of the device size. The coupler requirements are 90-degree phase shift between the output and the coupled ports and frequency bandwidth from about 10.5 GHz to 12.5 GHz. The design and optimization of the couplers have been performed by using the software CST Microwave Studio©. Eight different coupler configurations have been designed and compared. The better three couplers have been fabricated and characterized. The proposed SIW directional couplers could be integrated within more complex planar circuits or utilized as stand-alone devices, because of their compact size. They exhibit good performance and could be employed in communication applications as broadcast signal distribution and as key elements for the construction of other microwave devices and systems.

An ultra wideband (UWB) monopole antenna with dual band-notch characteristic is proposed. Dual arm spiral resonators (DASR) are placed on both sides of the feed line to create band notches at 5.25 and 5.8 GHz for the upper and lower WLAN bands respectively. First the antenna is optimized individually for both upper and lower WLAN band-notch behaviors then embedded together for dual band-notch characteristic. The measured results ensure that two band notches are achieved, and the antenna can be used for UWB applications without any interference from WLAN band.

It is a common synchronization approach of the bistatic Synthetic Aperture Radar (BiSAR) with spaceborne/stationary configuration that obtains synchronization information from a direct signal. An easy and effective synchronization method is using the direct signal as a match filter to compress the echo for range compression. This method requires a high signal-to-noise ratio (SNR) of the direct signal, because the low SNR of the direct signal affects the synchronization result. Furthermore, it affects the imaging quality and bistatic-InSAR (BiInSAR) result seriously. Two factors affect the SNR of the direct signal: low gain and saturation. The transmitter and receiver antenna beam patterns cause the received direct signal's power variance during the exposure time. The requirement of high gain and no saturation cannot be satisfied simultaneously during the exposure time when the receiver sub-system does not have automatic gain control (AGC). In this paper, a modified synchronization approach is proposed. The proposed method not only tolerates the low gain and saturation, but also does not require the parameters of the transmitted signal, such as FM chirp rate, bandwidth and transmitted pulse length. The proposed method makes the gain design of the synchronization channel easy. The experiment results verifies the effectiveness of the proposed approach.

For microwave tomography applications, we show that the utilized incident field distribution can affect the achievable image quantitative accuracy and resolution. In particular, for the synthetic cases considered here, it is shown that the use of a focused incident field distribution within the imaging domain often results in either enhanced or equivalent image reconstruction as compared to the use of an omnidirectional incident field distribution.

The traditional pattern synthesis method of space-borne array is to achieve a ``iso-flux'' beam coverage via approximating a desired pattern; however, the synthesized pattern may not optimize the whole satellite communication (SatCom) system performance. This paper analyzes the interference in multibeam SatCom system using CDMA, and establishes the relation model between user capacity and multibeam pattern. Additionally, a novel particle swarm optimization (PSO) based on simulated annealing (SA) pattern synthesis method is proposed, which chooses user capacity as synthesis objective function. The numerical analysis, which is performed for a hexagonal array with 19 stacked patch elements, confirms that user capacity is at least doubled with the ``max-gain-flux'' beam coverage implemented by our method, compared to the ``iso-flux'' coverage when communication outage probability is 10%.

A novel compact planar monopole antenna for UWB applications is proposed in this paper. The proposed novelty of the antenna is attributed to the addition of suitable beveled stubs to a basic circular geometry of the radiator as an improved impedance matching technique to achieve enhanced radiation performances. The feed circuit is a tapered microstrip line with a matching section over a semi-elliptical ground plane. The proposed antenna achieves sufficient impedance bandwidth for a VSWR<2 for frequencies from 3-15 GHz covering the entire UWB range (3.1-10.6 GHz), which is verified experimentally. Also this design achieves good gain, constant group delay and a near omni-directional radiation pattern over the UWB band. The UWB characteristics of the antenna are evaluated in frequency and time domains. Results reveal that the proposed antenna has flat transfer function, linear phase and good impulse response with virtually no ringing which are the essential requirements for an UWB antenna for efficient pulse transmission/reception. The simulated and measured results of these parameters are presented. The performance results of the novel antenna with other designs is also compared and presented.